037
AWIO20 FMEE 141245

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/14 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Monsoon Trough (MT) pattern east of 60oE. Under the influence of several equatorial waves (Rossby,...), the convective activity remains strong especially on the northern side of the MT and around two low pressure areas: one in the Australian AoR and one south of Diego Garcia.

Large low-pressure area south of the Chagos:

Since yesterday, the convective activity has fluctuated a lot in the region, and the maximum of vorticity monitored yesterday seems to have disappeared. Microwave images and this morning's Scatsat swath also seemed to indicate a new location of vorticity around 13.6S/75.7S but this too seems to have disappeared. This afternoon, convective activity seems to be organised around a mid-level circulation around 11.9S/73.4E but the latest microwave images (GMI 1005Z) do not show any significant curvature in the l
ow levels. In this context, combined with an poorly efficient convergence on the equatorial side, the risk of cyclogenesis in the next 24 hours seems rather low.

By the end of the weekend, this low will evolve into increasingly favourable environmental conditions. The low level convergence on the polar side will strengthen on Saturday and improve on the equatorial side. In upper levels, moderate easterly then north-easterly shear should remain present over the next 48 hours before weakening on Saturday under the upper ridge. The upper divergence should also significantly strengthen in the north-western quadrant on Saturday.

A cyclogenesis seems therefore likely during the weekend. The numerical models are in good agreement with this scenario but differ on the timing of this intensification. At longer range, while moving westward, this system could threaten inhabited lands especially Madagascar.

West of the Chagos, the risk of a moderate tropical storm is low tomorrow Friday, becomes moderate on Saturday and then high on Sunday.

In the Australian area :

A low pressure circulation is present around 13.1S 96.8E according to the latest Tropical Cyclone Outlook for the Western Region at 05UTC in a sheared environment. It could intensify in the next few days as it approaches our area of responsibility with the temporary drop in shear. It should cross 90E on Sunday in a still conducive environment. Thereafter, the environmental conditions should clearly deteriorate with the arrival of a strong west-north-westerly shear early next week ahead of an upper trough.

On the extreme East of the basin, the risk of formation or entry of a moderate tropical storm becomes moderate from Sunday onwards.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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129
AWIO20 FMEE 151243

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/15 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil but warnings WTIO20 and WTIO30 to be issued at 18Z, on Zone of Disturbed Weather 07-20202021.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Monsoon Trough (MT) pattern east of 60oE. Under the influence of several equatorial waves (Rossby,...), the convective activity remains strong especially on the northern side of the MT and around two low pressure areas: one in the Australian AoR and one south of Diego Garcia.

Zone of disturbed weather 07-20202021, south-west of the Chagos:

Since yesterday, convective activity is mainly present in the western semicircle of a large surface low pressure circulation under the influence of a strong east-northeasterly shear. ASCAT and Scatsat swaths confirm this with maximum winds close to 25kt far from the center in the southern semicircle.

This weekend, this low will evolve into increasingly favourable environmental conditions. The low level convergence will improve on the equatorial side. In upper levels, is expected to weaken progressivly under the upper ridge. The upper divergence should also significantly strengthen in the north-western quadrant on Saturday.

A cyclogenesis seems therefore likely during the weekend. The numerical models are in good agreement with this scenario but differ on the timing of this intensification. Early next week upper conditions may deteriorate with an increasing north-easterly shear. However latest numerical guidance still suggest a deepening onwards probably due to the swift movement in the same direction as shear. This system could threaten inhabited lands especially Madagascar eastern coastline in the middle of next week.

West of the Chagos, the risk of a moderate tropical storm is moderate on Saturday and then high on Sunday.

Tropical Depression in the Australian area :

A tropical depression is monitored by the BOM near 15.1S 95.2E according to the latest IDW27600 (Tropical Cyclone Technical Bulletin) at 06UTC, in a sheared environment. It is expected to intensify in the next few days as it approaches our area of responsibility with the temporary shear decrease. It should cross 90E during the day on Sunday or the following night in a still favorable environment. Thereafter, the environmental conditions should clearly deteriorate with the arrival of a strong west-northwest
shear at the beginning of next week in front of an upper trough.

On the extreme East of the basin, the risk of formation or entry of a moderate tropical storm becomes moderate from Sunday onwards.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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488
AWIO20 FMEE 161121

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/16 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 no003/7 and WTIO30 no3/7/20202021 issued at 06Z on tropical depression no07-20202021.

Next warnings at 12Z.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The monsoon flow is established over the entire basin. The convective activity over the basin is essentially present within the clockwise circulation of tropical depression no07 and within the tropical low present in the Australian zone. Rainstorm activity, without the presence of a suspicious zone, is located in the North and North-West of Madagascar.

Tropical depression no07-202021 :

Position at 09Z: 12.5oS / 65.6oE
Max wind over 10 minutes: 30 kt
Central pressure: 998 hPa
Current motion: West-Southwestwards at 8 kt

For more information, please refer to the bulletins issued at 06Z and followings.

The risk of this system becoming a moderate tropical storm becomes high from Sunday onwards.

Tropical low in the Australian zone :

A tropical low continues to be tracked by the BOM around 16.6S 92.5E according to the latest Tropical Cyclone Technical Bulletin (IDW27600) of 06UTC. This system is still intensifying and is expected to reach 90E late next night or Sunday, potentially as a severe tropical storm. Thereafter, environmental conditions are expected to deteriorate significantly as vertical wind shear increases early next week.

On the extreme east of the basin, the risk of a tropical storm entering is very high from Sunday.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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576
AWIO20 FMEE 181055

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/18 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 n/11/7/20202021 issued at 06Z on moderate tropical storm no07 ELOISE.

Warnings WTIO20 and WTIO30 n/4/8/20202021 issued at 06Z on moderate tropical storm no08 JOSHUA.

Next warnings at 12Z.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The monsoon flow is well established at the equator over the whole basin. It converges well with the clockwise circulations associated to the two tropical systems currently located over the basin. Convection is mainly located around ELOISE and JOSHUA but also within the slowing area of the monsoon flow between 65E and 85E.

Moderate Tropical Storm no07 ELOISE :

Position at 09Z: 14.1oS / 55.6oE
Max wind over 10 minutes: 40 kt
Central pressure: 993 hPa
Current motion: West Southwestwards at 14 kt
For more information, please refer to the bulletins issued at 06Z and followings.

Moderate Tropical Storm no08 JOSHUA :

Position at 09Z: 19.4oS / 86.8oE
Max wind over 10 minutes: 40 kt
Central pressure: 994 hPa
Current motion: West Southwestrwards at 6 kt
For more information, please refer to the bulletins that will be issued at 12Z and followings.

coming from the

From the middle of next week, some members of the european ensemble and even some deterministic model runs are suggesting the entrance of a new tropical storm on the East of the basin, coming from the australian AoR. Given the forecast guidance currently available,
the risk that a new tropical storm enters the basin from the East is deemed very low from Friday.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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998
AWIO20 FMEE 201044

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/20 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no19/7/20202021 issued at 06Z on Overland Depression no07 ELOISE.

Next warnings issued at 12Z.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The monsoon flow is well established at the equator West of 48E and East of
6E.

It converges mainly with the ELOISE's circulation, currently located over northern Madagascar.

A Monsoon Trough (MT) is located around 9S between 64E and the Eastern end of the basin.

The convection activity is mainly concentrated around the overland depression ELOISE, near the filling low JOSHUA and the northern part of the monsoon
rough.

Overland depresion no07 ELOISE :

Position at 09Z: 15.7S / 47.3E

Max wind over 10 minutes: 30 kt

Central pressure: 998 hPa

Current movement: West at 12 kt
For more information, please refer to the bulletins issued at 06Z and
ollowing.

Filling low no08 JOSHUA :

Position at 09Z: 21.6oS / 79oE

Max wind speed over 10 minutes: 25kt in the South quadrant.

Central pressure: 1008 hPa

Current movement: West 12 kt

It's going to track in a general west-southwest direction on the northern edge of the subtropical ridge, finishing filling up in the next few days.

Beyond the present forecast, the latest ensemble and deterministic models detect a suspicious zone, currently located in the Australian AoR. The last guidances see the possible coming of a new tropical storm on the extreme East of our AoR during the second half of next week.

The timing is still very uncertain at these ranges, and the numerical models remain quite divergent to propose a solid scenario.

Also, according to this analysis, the risk of a new tropical storm entering the extreme East of the basin is considered low as of Monday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
ext
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343
AWIO20 FMEE 210952

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/21 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no24/7/20202021 issued at 06UTC on moderate tropical storm no07 ELOISE.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough configuration centered from 7oS/50oE to 13oS on the eastern end of the basin. This configuration induces a well-established monsoon flow west of 50E which notably feeds the northern part of ELOISE. The convective activity is mainly concentrated around the moderate tropical storm ELOISE and at the eastern end of the basin, on the western part of a circulation currently over the Australian basin. Weak to moderate convective activity is also noticeable in the southeastern secto
r of the remnant low JOSHUA, located around 23oS/76oE.

Moderate tropical storm no07 ELOISE :

Position at 09UTC: 16.8S / 42.5E

Max wind over 10 minutes: 40 kt

Central pressure: 992 hPa

Displacement: West-South-West at 12 kt
For more information, please refer to the bulletins issued at 06UTC and following.

The latest ensemble and deterministic models detect a suspicious area, currently located in the Australian area of responsibility. The latest guidance forecasts the possible entry of this new tropical storm on the extreme east of our area of responsibility during the second half of next week.

The timing is still very uncertain at these times, and the numerical models remain quite divergent to propose a solid scenario.

Also, according to this analysis, the risk of a new tropical storm entering the extreme East of the basin is considered low as of Tuesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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343
AWIO20 FMEE 210952

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/21 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no24/7/20202021 issued at 06UTC on moderate tropical storm no07 ELOISE.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough configuration centered from 7oS/50oE to 13oS on the eastern end of the basin. This configuration induces a well-established monsoon flow west of 50E which notably feeds the northern part of ELOISE. The convective activity is mainly concentrated around the moderate tropical storm ELOISE and at the eastern end of the basin, on the western part of a circulation currently over the Australian basin. Weak to moderate convective activity is also noticeable in the southeastern secto
r of the remnant low JOSHUA, located around 23oS/76oE.

Moderate tropical storm no07 ELOISE :

Position at 09UTC: 16.8S / 42.5E

Max wind over 10 minutes: 40 kt

Central pressure: 992 hPa

Displacement: West-South-West at 12 kt
For more information, please refer to the bulletins issued at 06UTC and following.

The latest ensemble and deterministic models detect a suspicious area, currently located in the Australian area of responsibility. The latest guidance forecasts the possible entry of this new tropical storm on the extreme east of our area of responsibility during the second half of next week.

The timing is still very uncertain at these times, and the numerical models remain quite divergent to propose a solid scenario.

Also, according to this analysis, the risk of a new tropical storm entering the extreme East of the basin is considered low as of Tuesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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775
AWIO20 FMEE 221050

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/22 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no27/7/20202021 issued at 06UTC on severe tropical storm no07 ELOISE.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough configuration. It is centered from 7oS/55oE to 12oS on the eastern end of the basin. The resulting monsoon flow is well established west of 55E and feeds a low to moderate convective activity on the northern side of this trough. The rest of the weak to moderate convective activity is focused along a pseudo-warm front extending from the Seychelles to the west of Reunion Island, which is weakening. The main convective activity in the basin is focused near the severe tropical s
torm ELOISE.

Severe tropical storm no07 ELOISE :

Position at 09UTC: 19.2S / 37.6E

Max wind over 10 minutes: 60 kt

Central pressure: 986 hPa

Displacement: West-South-West at 12 kt
For more information, please refer to the bulletins issued at 06UTC and following.

Currently followed by the BOM via bulletin IDW27700, the moderate tropical storm (following the terminology of our basin) 10U presents a risk of entering our basin in the middle of next week, according to the forecasting of certain guidances.

The timing is still very uncertain at these deadlines, and the certain numerical models do not confirm in this re-entry.

Also, according to this analysis, the risk of a new tropical storm entering the extreme East of the basin is considered low as of Wednesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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747
AWIO20 FMEE 231053

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/23 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO24 and WTIO30 no31/7/20202021 issued at 06UTC on moderate tropical storm no07 ELOISE.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The monsoon flow is well established on the entire basin. However, trade winds remain weak over the central part of the basin, which does not define a clear monsoon trough pattern by lack of poleward convergence. The convective activity is mainly concentrated around ELOISE which made landfall on Mozambique last night. East of the basin, a weak system is located in the australian AoR.

Overland Depression no07 ELOISE :
Position at 09UTC: 20.6S / 33.6E
Max wind over 10 minutes: 35 kt
Motion: West-South-Westward at 9 kt
For more information, please refer to the bulletins issued at 06UTC and following.

Currently monitored by BOM through the IDW27700 bulletin (Tropical Cyclone Outlook), the tropical depression (according to the SWIO classification) 10U is currently affected by a moderate Easterly shear. It could enter our basin from the middle of next week. However, some models as well as some ensemble members still suggest a later entrance. Futhermore, mid-level dry air and the persistance of a weak upper Easterly shear constraint are rather unconducive for reintensification in the mid-term.

Also, according to this analysis, the risk of a new tropical storm entering the extreme East of the basin is considered low as of Wednesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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109
AWIO20 FMEE 241049

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/24 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO30 no35/7/20202021 issued at 06UTC on the overland depression no07 ELOISE.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The monsoon flow is well established on the entire basin. However, trade winds remain weak over the central part of the basin, which does not define a clear monsoon trough pattern by lack of poleward convergence.

The convective activity is mainly concentrated around ELOISE which now operates on land in northern South Africa close to the borders with Zambabwe and Botswanamade.

East of the basin, a weak system is located in the australian AoR.

Overland Depression no07 ELOISE :
Position at 09UTC: 23.1S / 29.8E
Max wind over 10 minutes: 25 kt
Pression : 998 hPa
Motion: South-Westward at 11 kt
For more information, please refer to the bulletins issued at 06UTC and following.

Currently monitored by BOM through the IDW10800 bulletin (Tropical Cyclone Outlook), the tropical depression (according to the SWIO classification) 10U is currently affected by a moderate Easterly shear. It could enter our basin from the middle of next week. However, some models as well as some ensemble members still suggest a later entrance. Futhermore, mid-level dry air and the persistance of a weak upper Easterly shear constraint are rather unconducive for reintensification in the mid-term.

Also, according to this analysis, the risk of a new tropical storm entering the extreme East of the basin is considered low as of Wednesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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955
AWIO20 FMEE 161104

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/16 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO24 and WTIO30 no01/11/20202021 on tropical disturbance no11.

Next warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


East of 65E, the basin is in a monsoon trough (MT) pattern with a MT centered around 10S. On the western side of the basin, the monsoon flow keeps a marked meridian component between the equator and 20S, especially near the African coast, converging towards a low-pressure area located in the southern Mozambique Channel, in which system no11 is embedded.

Convective activity in the basin is essentially present in the central and southern part of the Mozambique Channel in connection with system no11, as well as on the equatorial side of the MT in the slowing down zone of the monsoon flow, but also in the vicinity of weak low pressure areas near the Mascarene Islands, including FARAJI's remnants.

Tropical disturbance no11-20202021 :
Position at 09UTC : 21.3S / 35.5E
Estimated minimum pressure: 995hPa
Max wind over 10 minutes: 25kt
Movement: N, 4kt.

System no11 presents a high risk of developing into a Moderate Tropical Storm in the next 48 hours.
For more information, please refer to the next bulletins issued at 12UTC and following.

Apart from system no11, there is no risk of another tropical storm forming in the basin in the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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764
AWIO20 FMEE 171104

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/17 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO24 and WTIO30 no05/11/20202021 on tropical depression no11.

Next warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


East of 65E, the basin is in a monsoon trough (MT) pattern with a MT centered from 8S to 13S, eastwards. On the western side of the basin, the monsoon flow keeps a marked meridian component between the equator and 23S, especially near the African coast, converging towards a low-pressure area located in the southern Mozambique Channel, in which system no11 is embedded.

Convective activity in the basin is essentially present in the central and southern part of the Mozambique Channel in connection with system no11, as well as on the equatorial side of the MT in the slowing down zone of the monsoon flow, but also in the vicinity of weak low pressure areas near the Mascarene Islands, including FARAJI's remnants.

Tropical depression no11-20202021 :
Position at 09UTC : 21.0S / 37.4E
Estimated minimum pressure: 993hPa
Max wind over 10 minutes: 30kt
Movement: S, 2kt.

System no11 presents a high risk of developing into a Moderate Tropical Storm in the next 24 hours.
For more information, please refer to the next bulletins issued at 12UTC and following.

Apart from system no11, there is no risk of another tropical storm forming in the basin in the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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334
AWIO20 FMEE 180943

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/18 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO24 and WTIO30 no09/11/20202021 on moderate tropical storm no11 GUAMBE.

Next warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


East of 60E, the basin is in a monsoon trough (MT) configuration oriented towards 10S. To the west of the basin, the monsoon flow is well present and concerns the entire Mozambique Channel, converging towards the moderate tropical storm GUAMBE.

The strong convective activity over the basin is mainly present at the area of tropical storm GUAMBE. The activity is more modest at the area of MT in the zone of slowing down of the flow towards 68E and further south east of the Mascarene Islands in the convergence of the flow induced by the development of a low pressure area in connection with the dynamics of altitude and the remnants associated with FARAJI.

Moderate Tropical Storm GUAMBE :
Position at 09UTC: 23.3S / 37.7E
Estimated minimum pressure: 983hPa
Max wind over 10 minutes: 45kt
Displacement: South 4kt.
For more information, please refer to the next bulletins issued at 12UTC and following.

There is no risk of another tropical storm developing on the basin in the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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804
AWIO20 FMEE 191214

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/19 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO24 and WTIO30 no13/11/20202021 on tropical cyclone no11 GUAMBE.

Next warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) pattern along 10S. Lower convergence increased over the western part of the basin and convective activity is quite strong there. Tropical cyclone GUAMBE is now indepedent from the MT and moves southward in the southern Mozambique Chanel near 25S.

Tropical Cyclone GUAMBE :
Position at 09UTC: 24.6S / 36.7E
Estimated MSLP : 963hPa
Max wind over 10 minutes: 75kt
Movement : South-West 5kt.
For more information, please refer to the next bulletins issued at 12UTC and following.

North-East of Madagascar :

Next week, surface convergence and convective activity are expected to increase thanks to the meeting of two equatorial waves : Equatorial Rossby arriving from the east and Kelvin coming from the west. Convergence on the polar side should also strengthen with the establishment of a new anticyclonic cell to the south beyond Sunday. In this favorable context, a low level circulation should develop in the MT northeast of Madagascar and benefit from a low shear environment.

Although some determinist guidance, especially the last runs of the GFS, suggest the formation of gale force winds before next Thursday, the european EPS forecast a fairly low risk for the next 5 days at present.

The likelihood for the development of an other moderate tropical storm over the basin becomes very low from Wednesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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315
AWIO20 FMEE 201147

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/20 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO24 and WTIO30 no17/11/20202021 on tropical cyclone no11 GUAMBE.

Next warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) pattern along 10S. Two main low pressure areas are located within the MT where the concentrate most of the convective activity ion their northern side, one to the north-east of Madagascar and the other on the easternmost parts of the basin. Convective activity is rather strong also near GUAMBE in the southern Mozambique Channel.

Severe Tropical Storm GUAMBE :
Position at 09UTC: 26.1S/36.1E
Estimated MSLP : 980hPa
Max wind over 10 minutes: 55kt
Movement : South 6kt.

Wind data estimated by a SAR satellite (Radarsat2) at 0304Z this morning show that the GUAMBE inner core is weaker than analysed at 06Z (max wind around 50-60 kt on the swath) probably due to an eyewall replacement cycle. The final intensity at 06Z (and 09Z) is now assessed at 55 kt accordingly.

For more information, please refer to the next bulletins issued at 12UTC and following.

North-East of Madagascar :

The latest observations (satellite images and scatterometric data) show the building of a low pressure area with currently no apparent center, between the northeast of Madagascar and Agalega.

In the coming days, large-scale conditions will be favorable for the development of this low pressure area with a strong upper divergence thanks to the passage of a Kelvin wave and the building of an MJO signal in the phase 2. Surface vorticity also seems to be reinforced by the presence of an Equatorial Rossby wave.

In this favorable context, the low pressure circulation should gradually strengthen and a minimum is expected to form on Monday or Tuesday. This minimum should benefit from a low shear environment, conducive to its deepening at first. The upper divergence could be temporarily increased on Monday and Tuesday by the passage of a weak cut-off north of the Mascarene Islands. The latest deterministic models seem to be in good agreement and most suggest the formation of a moderate tropical storm on Tuesday or We
dnesday, with the exception of UKMO whose low interacts too quickly with Madagascar. The ensemble forecasts are also quite reactive suggesting a significant risk.

The likelihood for the development of an other moderate tropical storm over the basin becomes low on Tuesday and moderate from Wednesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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608
AWIO20 FMEE 211147

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/21 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO24 and WTIO30 no21/11/20202021 on severe tropical storm no11 GUAMBE.

Next warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:

The basin is in a Monsoon Trough (MT) pattern axed between 13S and 10S east of 50oE. A low pressure area concentrates the associated convective activity at the western end of the MT near northeastern Madagascar. Convective activity is also strong but fluctuating in the south of the Mozambique channel near GUAMBE.

Severe tropical storm GUAMBE :
Position at 09UTC: 30.1S / 38.4E
Estimated minimum pressure: 984 hPa
Max wind over 10 minutes: 50 kt
Forward motion: South-East 12 kt

For more information, please refer to the next bulletins issued at 12UTC and following.

In a large-scale context favorable to cyclogenesis in the western part of the basin (development of a moist phase of the MJO + significant activity of other equatorial waves), it seems likely that a new tropical storm will form west of 70oE next week.

North-East of Madagascar :

An area of low pressure remains present North-East of Madagascar with a very poorly defined and elongated center estimated according to the Ascat-B of 0623Z around 12.6S and 51.2E. Winds are estimated at 10/20 kt and the minimum pressure within the area is 1008 hPa. The convective activity shows no sign of organization compared to yesterday and the environmental pressures show little change in 24 hours.

If the low levels conditions are globally favorable over the period, especially on the northern side, it is at mid and upper levels that the environment is a little more mixed. Indeed, in the first part of next week, a cut-off low will circulate in the South of this suspect zone. Its influence will be double with an improvement of the upper levels divergence but also an advection of dry air in the mid troposphere (clearly visible in water vapor imagery). The models react very differently in response to this
context by sheltering more or less the suspect area from the dry air associated with the cut-off. The timing and location of this potential cyclogenesis becomes therefore very uncertain.

The risk of formation of another moderate tropical storm on the basin becomes low from Tuesday and remains moderate from Wednesday to the northeast of Madagascar.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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469
AWIO20 FMEE 221201

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/22 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO24 and WTIO30 no25/11/20202021 on Post-Tropical Low no11
x-GUAMBE.

Last warnings.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Monsoon Trough (MT) pattern with a MT centered between 13S and 10S over the entire basin. Several areas of vorticity are embedded within the MT : the main ones are described hereafter. The large scale context is globally favourable to cyclogenesis in the western part of the basin (development of a wet phase of the MJO + activity of other equatorial waves, in particular Kelvin and Rossby-gravity).

Around northwestern Madagascar and eastern Comoros, a first area of vorticity is present, associated with enhanced convection. The atmospheric environment is humid on the equatorial side, but dry air is present to its immediate south in the central Mozambique Channel. Surface convergence seems to be well-established on the equatorial side but more fragile on the polar side. Vertical wind shear will be temporarily moderate over the area in the coming days. In these mixed conditions, ensemble models have revi
sed the risk of storm formation in the vicinity of northern Madagascar and in the northern Mozambique Channel a little downward.

Off the north-eastern coast of Madagascar, a second area of vorticity should strengthen a little later this week to the south of Agalega, benefiting from good low-level convergence between the monsoon flow and the trade winds. On the other hand, dry air could be advected on the polar side, making the potential for cyclogenesis uncertain.

Finally, on the eastern side of the basin, between 75 and 80oE, a third area of vorticity could form, under the action of a strong surge in the monsoon flow. Nevertheless, despite favorable conditions on the equatorial side, the presence of a mid-tropospheric cut-off further south should disrupt the convergence on the polar side and potentially advect dry air near this area, hence the still fragile potential.

About these different suspicious areas, deterministic and ensemble models are still quite dispersed and fluctuating from one run to another, hence a predictability that remains limited.

The risk of formation of a new moderate tropical storm on the basin becomes :

- very low from tomorrow on the north of the Mozambique Channel,

- very low from Friday between the south of Agalega and the northeast of Madagascar,

- very low from Friday on the east side of the basin.

Ex-GUAMBE is now leaving the basin and moving away towards the southern mid-latitudes while losing its tropical characteristics.
Post-Tropical Low ex-GUAMBE :
Position at 09UTC: 37.3S / 51.6E
Estimated minimum pressure: 987 hPa
Max wind over 10 minutes: 60 kt
Movement: South-East 50 kt
For more information, please refer to the bulletin issued at 06UTC, the last on this system.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$

a
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337
AWIO20 FMEE 231226

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/23 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Monsoon Trough (MT) pattern with a MT centered between 10 and 13S across the entire basin. Several areas of vorticity are embedded within the MT. The large scale context is globally conducive for cyclogenesis in the western part of the basin thanks to the development of a wet phase of the MJO, in phase with other equatorial waves, in particular Kelvin and Rossby-gravity.

In the northern Mozambique Channel, a first area of vorticity is centered close to Glorieuses islands this Tuesday, associated with enhanced convection. The atmospheric environment is humid on the equatorial side, but dry air is present to its immediate south in the central Mozambique Channel. Surface convergence is well-established on the equatorial side. However, vertical wind shear will be temporarily moderate over the area in the coming days. In these mixed conditions, the risk of storm formation in the
vicinity of northern Madagascar and in the northern Mozambique Channel should remain low from tomorrow. Later on, this weekend, a trade-wind surge should enhance low-level convergence in the Channel, which could also help trigger storm formation in that area.

More to the east along the MT in the Indian ocean, an other area of vorticity should strengthen in a few days near 11-12S and 56-65E (south-east of Agalega), benefiting from good low-level convergence between the monsoon flow and the trade winds. On the other hand, dry air could be advected on the polar side, thus keeping the cyclogenesis potential quite uncertain.

Finally, on the eastern side of the basin, most NWP models have dropped the chances of a new system forming close to 80E. But the chances of a new storm forming east of 90E have significantly picked up by this weekend. The chances that this potential new storm should cross into the SWIO area of responsibility before next Monday are very low but the possibility can't be completely ruled out.

The risk of formation of a new moderate tropical storm on the basin becomes low from tomorrow in the vicinity of the north of the Mozambique Channel and very low from Friday to the south-east of Agalega.

The risk of a new tropical storm entering the eastern edge of the basin becomes very low from Sunday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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238
AWIO20 FMEE 241019

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/24 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Monsoon trough (MT) configuration centered between 10S and 14S east of 50E. For the present, the vorticity zones present within this MT remain sufficiently weak not to define a significant potential for cyclogenesis, particularly in the northern part of the Mascarene Islands. On the other hand, convective activity is present on the equatorial side of this MT, in the zone of slowing monsoon flow.

In the northern part of the Mozambique Channel, an onset of monsoon flow can also be noted, causing moderate to strong convective activity at the northern tip of Madagascar. This onset of monsoon flow will only materialize later in the WE, bringing rainfall to the northern area of the Mozambique Channel. Thereafter, under the effect of a push of trade winds on the polar side on the south of the Channel helped by the maintenance of the monsoon flow in the northern sector of the Channel, the convergence shoul
d strengthen and allow a low risk of cyclogenesis for Tuesday in the Channel.

The risk of a moderate tropical storm forming in the Mozambique Channel becomes low from Tuesday onwards.

On the eastern end of the basin, the entry into our area of responsibility of a tropical system coming from the Australian area of responsibility, currently mentioned in the IDW10800 bulletin issued by the BOM, could occur next Monday or Tuesday.

The risk of entry of a new system from the eastern part of the domain becomes moderate from Tuesday onwards.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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137
AWIO20 FMEE 251210

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/25 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO30 no39/7/20202021 issued at 06UTC on the overland depression no07 ELOISE.

Last warning for this system.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The monsoon flow is well established west of 56.5E, and remains less pronounced over the rest of the basin, where it is more zonal in orientation. The lower level convergence on the polar eastern side remains weak, due to the weakness of the ridge centered on the southeast side of the basin. Thus, it's quite difficult for the moment, to draw a clear monsoon trough axis. This will be easier in the end of the week.

The convective activity is rather weak now around ELOISE Overland Depression, which is currently evolving on land near the border between South Africa and Botswana. On the other hand, convective activity is moderate to fairly strong over the northern part of the MT, over the extreme eastern part of the basin and also near a tropical disturbance that is currently evolving 700 km southwest of the Eastern Coco Islands in the Australia's AoR.

Overland depression no07 ELOISE :

Position at 1030UTC: 24.2S / 25.2E

Max wind over 10 minutes: 15 kt

Pressure: 1007hPa.

Current movement: West-South-West at 14 kt
For more information, please refer to the bulletins issued at 06UTC.

Currently monitored by the BOM through the IDW10800 bulletin, the tropical disturbance (in the terminology of our basin) located at 0600Z by 17.4S - 95.9E, is under the influence of a moderate eastern wind shear that weakens it. On the other hand, it is offset by a good lower level convergence on the polar side.

It could enter our basin in the middle of next week. However, some numerical models still suggest a later entrance. In addition, mid-level dry air and the persistence of a weak Easterly shear aloft should hinder a possible re-intensification in the medium range.

Also, according to this analysis, the risk of a new tropical storm entering the extreme East of the basin is considered low as of Wednesday.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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675
AWIO20 FMEE 261221

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/26 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The transequatorial monsoon flow is established over the whole width of the basin, rapidly shifting to westerlies between the equator and 10S. Low level convergence is weak on the polar side of the monsoon trough centered around 10/12S because of a weak and poorly organized trade wind regime caused by a a weak subtropical ridge.

The overall convective activity is weak across most of the basin and is mainly present north of 10S, although slightly enhanced near the Seychelles, in the Mozambique Channel as well as on the extreme northeastern side of the basin.

Overland depression no07 ELOISE :

The remnant low associated with ELOISE is still observed inland over southern Africa close to the border between South Africa and Botswana (the surface low was centered around 25.6S/22.9E this Tuesday at 09Z). The associated convective activity will continue to bring significant rainfall over the next 24 to 48 hours, particularly in north-central South Africa (over 100mm in 24 hours locally).

Tropical depression near the eastern border of our basin :

A tropical low monitored by the BOM is present in the Australian AoR, located near 18.5S/95.0S at 06Z this Tuesday (see IDW10800 bulletin). Its structure has improved this Tuesday afternoon due to a substantial decrease of the deep-layer wind shear (only 10kt) and to sufficient moisture surrounding the system.

These environmental conditions, combined with a good low-level convergence on the polar side of the system, are conducive for development in the very short run (next 24 hours or so).

Nevertheless, some dry air intrusions should occur from Wednesday, which should gradually weaken the system by the time it enters the SWIO AoR at 90E around Wednesday afternoon. At that time it could still be at tropical depression or tropical storm strength. On the southern side of the system, between 20S and 23S, winds should blow at near-gale to gale strength at least for Wednesday and Thursday.

With the subtropical high building up as from Wednesday, the easterly flow in which this system is evolving will accelerate, making it track faster in a west to west/north-west direction. On this track, the system should remain at a low to very low intensity (disturbance or tropical depression), still inhibited by a too dry and sheared mid-troposphere until Friday or Saturday.

During the weekend, NWP guidance shows a possibly more moist environment surrounding the system. Despite a persisting easterly shear, convection could be enhanced by some significant upper-level divergence on its western side. This could enable some intensification up to tropical storm strengh around Sunday to the north-east of the Mascareignes archipelago (between 60 and 70E and close to 15S). However, this remains a low probability option and there is no consensus in the panel of deterministic and ensembl
e models available.

The risk of a new tropical storm entering the extreme East of the basin becomes moderate on Wednesday.

After a weakening phase forecast in mid and late week, the risk of this system developping into a tropical storm to the north-east of the Mascareignes becomes low on Sunday.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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013
AWIO20 FMEE 271110

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/27 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Next warnings WTIO20 and WTIO30 no01/09/20202021 issued at 12UTC on tropical depression no09.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The major part of the basin is in a monsoon trough pattern, with a monsoon trough centered around 10/13S. On its equatorial side, the transequatorial monsoon flow rapidly shifts to westerlies between the equator and 10S. On its polar side, low level convergence remains weak due to a weak trade wind regime between 15S and the Tropic, on the northern edge of a poorly organised subtropical ridge. The latter should reconstitute more frankly to the southwest of the Mascarene Islands next weekend.

Convective activity associated with the ITCZ is mainly present north of 10S and east of 47E and generally weak over the remaining part of the basin. However, there is still strong rain and thunderstorm activity in the southeastern periphery of the remnant low ELOISE located over northern South Africa, but this activity is becoming increasingly dissociated from the depression itself and is being shifted quite far to the southeast of it. Indeed, a strong baroclinic interaction on the edge of a trough circulat
ing south of South Africa is triggering frontogenesis over southeastern South Africa, extending over the Southern Ocean further southeast where a baroclinic cyclogenesis should form between Wednesday evening and Thursday in the vicinity of 32/35S and 35/40E at the warm entrance of a powerful high-altitude jet stream, but without any risk that this depression will take on tropical characteristics.

Moreover, a new low pressure system is approaching the SWIO basin from the east this Wednesday, around 20S, coming from the Australian AoR (see below).

Tropical Depression 09 on the eastern edge of the basin (entering our area of responsibility) :
Position at 09UTC: 19.6S/91.1E
Estimated minimum pressure: 1001hPa
Max winds over 10 minutes: 30kt
Movement: West-Southwest at 7kt

For more information, please refer to the next bulletins issued.

Over the next five days, there is no risk of another moderate tropical storm forming in our basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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072
AWIO20 FMEE 281112

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/28 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Next warnings WTIO20 and WTIO30 no02/09/20202021 issued at 12UTC on tropical depression no09.

Last issues for this system.

PART 2 :
TROPICAL WEATHER DISCUSSION:

The basin remains in a monsoon trough (MT) pattern over most of the northern part of the basin.

The MT is centered around 12/13S, with a monsoon flow turning rapidly to the West sector between the equator and 6S on the MT's equatorial side. On the polar side, the lower level convergence remains weak in connection with weak trade winds flow between 15S and the Tropic of Capricorn, north of a subtropical ridge of low troposphere fragmented and not very intense. This should reconstitute more strongly southwest of the Mascarene Islands as of next weekend.

The convective activity of the ITCZ is present in the basin over multiple
ones:

- In the area of slowing transequatorial flow, on the northern edge of the MT, between the equator and 4S, east of 68E.

- In the zone of slowing monsoon flow, in the northern Mozambique Channel, west of the Malagasy coast.

- In the western end of the TM between 10/18S and 60/68E, due to the altitude dynamics, which presents a warm jet inlet that instabilizes the warm air of the lower layers. This same dynamic, due to the presence of its cold air aloft, generates deep convection in the Mascarene area.

Tropical Depression no09 at the eastern end of the basin:

Position at 10UTC: 18.2S/85.3E

Estimated minimum pressure: 1003hPa

Max wind over 10 minutes: 30kt

Currently movement: West-Northwest at 15kt

For more information, please refer to the next bulletins issued at 12Z (the latest bulletins for this system)

Over the next five days, there is no risk of another moderate tropical storm forming in our basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
e
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382
AWIO20 FMEE 291211

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/29 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) pattern over most of the northern part of the basin.

The MT is centered around 11/12S, with a monsoon flow turning westerly between the equator and 7S on the MT's equatorial side. On its polar side, the LL convergence has slightly increased since yesterday with a better organized trade winds flow north of a rebuilding LL subtropical ridge south of 30S. Low no09 is embedded in the MT and is drifting westward while gradually weakening.

Filling Low no09 :
Position at 1030UTC: 17.4S/77.9E
Estimated minimum pressure: 1006hPa
Max wind over 10 minutes: 20/25kt, reaching 30kt quite far from the center in the southern quadrant due to gradient effect.
Current movement: West at 17kt

This weak system is currently being sheared by a moderate easterly deep-layer shear and surrounded by dry air in the mid-troposphere. Although LL convergence is good on the trade wind side, it is very badly organized on the equatorial side of the system. Over the next days, model guidance forecasts that these unfavorable conditions will persist at least until Monday or Tuesday in the vicinity of the system while it drifts westward, which will continue to keep it weak or even make it weaker. From Tuesday, ea
sterly shear should ease a bit and upper divergence could slightly increase under the influence of a subtropical upper-level trough circulating south of the system. Besides, LL convergence is expected to improve equatorward. Consequently, some model runs suggest a risk of intensification in the longer run.

Over the next five days, there is no risk of a moderate tropical storm forming in our basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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833
AWIO20 FMEE 301153

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/30 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) pattern over most of the northern part of the basin.

The MT is centered around 11/12S, with a monsoon flow turning westerly between the equator and 7S on the MT's equatorial side. On its polar side, the LL convergence is good on the northern side of the anticyclone. Filling Low no09 is embedded in the MT and is drifting westward while gradually weakening.

Filling Low no09 :
Position at 1030UTC: 16.2S/70.4E
Estimated minimum pressure: 1006hPa
Max wind over 10 minutes: 20/25kt, reaching 30kt quite far from the center in the southern quadrant due to gradient effect.
Current movement: West-North-West at 14kt

Over the next days, model guidance forecasts that unfavorable conditions will persist while drifting westward, which will continue to keep it weak or even make it weaker. Equatorial convergence is expected to remain quite weak preventing from any significant risk of deepening. Early next week, the low will probably merge with the MT, and so dissipate.

Over the next five days, there is no risk of a moderate tropical storm forming in our basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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618
AWIO20 FMEE 311127

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/31 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:

The basin remains in a Moonson Trough (TM) pattern East of 48E and is centered around 11/12S. It benefits from a good lower level convergence on the equatorial side, between 48E and 80E. The monsoon flow East of 80E turns rapidly westerly between the equator and 9S. On the polar side, the trade winds remains well present on the northern side of the subtropical ridge.

Within the MT, filling low no9, currently located 920 km from Reunion Island, is being drifting west-northwesterly, while gradually weakening.

Convective activity is mainly observed in the slowing of the monsoon flow north of the MT, as well as in the southern quadrant of the filling depression no9.

Filling depression no09 :

Position at 0930UTC: 14.9S/61.7E

Estimated minimum pressure: 1007hPa

Max wind over 10 minutes: 20/25kt away from the center in the South and Southeast quadrant by gradient effect.

Current movement: West-Northwest at 20kt

For the next five days, this low depression will track west-Northwesterly. Deterministic and ensemble models suggest unconducive conditions for its development, which should keep it weak or event make it weaker. The system should thus dissipate in the first part of next week.

In the second half of next week, the main guidances detect a suspicious low, within the TM, on the extreme North-East of the basin. At this point, the timing remains uncertain for the moment, and the models remain divergent to propose a solid scenario.

Also, According to the latest analysis, the risk of a new tropical storm entering the extreme East of the basin is considered very low as of Friday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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723
AWIO20 FMEE 021111

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/02 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Monsoon Trough (MT) east of 55E, centered around 10/11S. Good low-level convergence is present on its equatorial side . On the polar side of the TM, low-level convergence remains well marked on the north face of the subtropical anticyclone.

Within the TM, Depression No. 9, located about 860 km from Reunion Island, is currently drifting west northwestward and gradually filling.

The convective activity is mainly observed in the slowing of the monsoon flow north of the TM, east to 73E south of the TM as well as in the northwestern quadrant of the filling depression no9.

Filling depression no09 :

Position at 1000UTC: 13.0S/53.6E

Estimated minimum pressure: 1009hPa

Max wind over 10 minutes: 20kt far from the center, in the South quadrant by gradient effect.

Movement: West northwest at 10kt

For the next five days, this system will continue on a course towards the West-Northwest then northwest. Deterministic models suggest unfavourable conditions for its development, which should continue to weaken this already fragile circulation. The system is expected to dissipate by the end of week.

This weekend, some guidances detect a suspicious area on the extreme east of the basin, within the TM. However, models diverge about the timing and environmental conditions linked to this system. For the moment, chances of development remain very low.

The risk of a new tropical storm forming over the extreme east of the basin is considered very low as of Friday and low on Sunday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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440
AWIO20 FMEE 031123

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/03 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Monsoon Trough (MT) east of 50E, centered around 11/12S. It benefits from a good supply of low level convergence East of 71E, with a good equatorial convergence. On the polar side of the MT, the low level convergence remains well defined on the north side of the subtropical ridge.

Within the MT, northeast of Cap d'Ambre, Depression Number 9, located about 1150 km from Reunion Island, is currently tracking west-northwesterly, gradually filling up.

The convective activity is mainly observed in the slowing of the monsoon flow, north of the TM, as well as south of the MT east of 75E, in the northwestern and southern quadrant of the filling depression number 9 and in the north of the Mozambique Channel due to local low level convergences.

Filling Depression No. 9:

Position at 0900UTC: 11.9S/52.1E

Estimated minimum pressure: 1010hPa

Max wind over 10 minutes: 15kt away from the center in the South quadrant by gradient effect, according to the swath of this morning (Scat-Sat).

Current movement: West northwest at 7kt

For the next five days, this low will track West-Northwesterly. Numerical weather prediction suggest unconducive environmental conditions for its development, which should continue to weaken an already weak low level circulation. This system is expected to dissipate by the weekend.

Over the weekend, the main numerical guidance detect a suspicious area in the extreme east of the basin, nested in the monsoon trough. The timing remains unsure for the moment, and the numerical guidance remain divided to suggest a reliable consensus.

Thus, according to the latest analysis, the risk of a new tropical storm forming over the extreme east of the basin is considered low as of Friday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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452
AWIO20 FMEE 041130

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/04 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a well-defined monsoon trough (MT) pattern along 10S. Convection is mainly located on the equaorial side of the MT, within the slowing area of the monsoon flow. While the system nb 09 merged with the Western tip of the MT, a new clockwise circulation developed South-East of the Chagos.

A well-defined surface circulation appeared as a low-level clouds vortex on this morning sat animations, near 11.45S/81E at 06Z. This circulation begins to concentrate significant convective activity, while benefiting from conducive conditions currently : a nice monsoon feed in the low-levels and a good upper divergence aloft. Max winds are estimated at 20kt on each side of the circulation.

However, the environment is expected to become more neutral with decreasing low-level convergence and upper divergence. The available guidance also have mixed feelings about this environment and do not translate it as a deepening in every model run. The ensemble prediction illustrate this uncertainty with a moderate risk of cyclogenesis.

The risk of formation of a moderate tropical storm becomes moderate from Sunday South-East of the Chagos.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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778
AWIO20 FMEE 061000

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/06 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no05/10/20202021 on sever tropical storm Faraji.

Next Warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a well-defined monsoon trough (MT) configuration throughout the basin. It is oriented towards 10oS in the west of the basinand allso at the eastern end, and near Faraji. Convection is mainly present on the equatorial face of the MT, in the monsoon slowdown zone and near Faraji.

Severe Tropical Storm Faraji :
Position at 0900UTC: 14.3S/79.9E
Estimated minimum pressure: 985hPa
Max wind over 10 minutes: 55kt
Displacement: South 5kt
For more information, please refer to the next bulletins issued at 12UTC and following.

The monsoon flow starting on Saturday and then more frankly on Sunday in the North of the Mozambique Channel allows a wet feed that will last for several days. Under these conditions, the models forecast the establishment of a circulation that should intensify over the next few days and evolve into a moderate tropical storm in the middle of next week.

The risk of another moderate tropical storm formation becomes very low in the Mozambique Channel from Wednesday onwards, and low on Thursday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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848
AWIO20 FMEE 071157

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/07 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 no009/10 and WTIO30 no9/10/20202021 on intense tropical cyclone Faraji.

Next Warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) pattern centered between 10S and 13S east of 50E. In the Mozambique Channel, a weak monsoon flow converges to an area of low relative pressure located on the southern half of the channel. In the Indian Ocean, convective activity is moderate to strong on the northern side of the MT and very strong near cyclone FARAJI. In the Mozambique channel, convection is locally moderate, mainly on the northern half of the channel near the southern part of the Comoros archipelag
o.

Intense Tropical Cyclone FARAJI :

Position at 1000UTC : 14.7S/79.8E

Estimated minimum pressure: 939 hPa

Max wind over 10 minutes: 105kt

Forward motion: Quasi-stationary
For more information, please refer to the next bulletins issued at 12UTC and following.

On the Mozambique Channel:

The monsoon flow, currently in place on the northern part of the channel, will be maintained and reinforced this week by a baroclinic interaction between an upper levels trough arriving from the southwest and the low pressure area currently located on the southern part of the channel. In the second part of the week, with the shift of the upper levels trough towards the West, the environmental conditions become a little more conducive to a tropical cyclogenesis. However, the complexity of the meteorological
situation and the proximity of the land means that the signal for the formation of a storm remains weak for the moment and does not appear before the end of the forecast (Day 4 / Day 5).

In connection with this situation, the weather will become very disturbed during the week in the central and southern regions of the Mozambique Channel. Associated heavy rains may notably concern some regions of the West coast of Madagascar.

The risk of another moderate tropical storm will become low in the Mozambique Channel from Thursday onwards.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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425
AWIO20 FMEE 081126

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/08 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 no013/10 and WTIO30 no13/10/20202021 on intense tropical cyclone Faraji.

Next Warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) pattern centered between 10S and 13S east of 50E. In the Mozambique Channel, a weak monsoon flow converges in an area of low pressure located on the southern half of the channel. In the Indian Ocean, convective activity is weak to moderate on the northern side of the MT and strong near cyclone FARAJI. In the Mozambique channel, convection is locally strong, on the northern half of the channel.

Intense Tropical Cyclone FARAJI :

Position at 1000UTC : 14.1S/81.7E

Estimated minimum pressure: 940 hPa

Max wind over 10 minutes: 105kt

Forward motion: ENE 7kt
For more information, please refer to the next bulletins issued at 12UTC and following.

On the Mozambique Channel:

The monsoon flow, currently in place on the northern part of the channel, will increase this week thanks to a baroclinic interaction between an upper levels trough arriving from the southwest and the low pressure area currently located on the southern part of the channel. Later this week, with the shift of the upper levels trough towards the West, the environmental conditions become a little more conducive to a tropical cyclogenesis. However, the complexity of the meteorological situation due to the upper t
rough and the proximity of the land prevent from a strong signal for development, in a quite broad area south of the Channel.

Related to this situation, weather conditions will be disturbed during the week on the coastal regions of the Mozambique channel in Madagascar and Mozambique.

The risk that an other moderate tropical storm forms in the Mozambique Channel becomes low from Thursday onwards.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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213
AWIO20 FMEE 090944

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/09 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 no017/10 and WTIO30 no17/10/20202021 on intense tropical cyclone FARAJI.

Next Warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) configuration centered between 9S and 13S east of 50E. West of this MT, the monsoon flow concerns the entire Mozambique Channel and converges towards a low pressure zone located off the Mozambican coast around 21S/37.5E. The convective activity is focused at the level of intense tropical cyclone FARAJI, in the Mozambique Channel along the axis of the monsoon flow on its eastern part and more modestly on the northern side of the MT.

Intense Tropical Cyclone FARAJI :

Position at 0900UTC : 14.1S/83.9E

Estimated minimum pressure: 935 hPa

Max wind over 10 minutes: 110kt

Forward motion: E 5kt
For more information, please refer to the next bulletins issued at 12UTC and following.

On the Mozambique Channel:

The monsoon flow, currently in place in the channel, will strengthen over the next few days due to the baroclinic interaction between a high altitude trough rising from the South-West and the low pressure area in the South of the channel. The location near or on the land of the low pressure zone should not allow its deepening but rather favour the intensification of the monsoon flow. This situation should leave winds close to 35 knots over a good part of the canal.

Related to this situation, weather conditions will be disturbed during the week on the coastal regions of the Mozambique channel in Madagascar and Mozambique.

The risk that an other moderate tropical storm forms in the Mozambique Channel is low from Thursday onwards.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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911
AWIO20 FMEE 101206

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/10 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 no021/10 and WTIO30 no21/10/20202021 on tropical cyclone FARAJI.

Next Warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) configuration centered between 9S and 14S east of 50E. West of this MT, the monsoon flow concerns the entire Mozambique Channel and converges towards a low pressure zone located off the Mozambican coast around 22.7S/40.0E. The convective activity is focused at the level of tropical cyclone FARAJI, in the Mozambique Channel along the axis of the monsoon flow on its eastern part and more modestly on the northern side of the MT.

Tropical Cyclone FARAJI :

Position at 0800UTC : 15.3S/85.1E

Estimated minimum pressure: 962 hPa

Max wind over 10 minutes: 85kt

Forward motion: SSE 3kt
For more information, please refer to the next bulletins issued at 12UTC and following.

On the Mozambique Channel:

The monsoon flow, currently in place in the channel, will strengthen over the next few days due to the baroclinic interaction between a high altitude trough rising from the South-West and the low pressure area in the South of the channel.

On the satellite imagery we can discern a vortex near the island of Europa. The automatic station present on this island, shows a decrease in pressure.

The depression is shifting westward under the influence of the subtropical ridge, and is positioned at the end of Thursday under the through. The system remains under the axis of the trough on Friday, which could allow the formation of a warm core near the coast of Mozambique.

On Saturday, the through shifted towards the North- West, and the system could then deepen into a moderate tropical storm on the western edge of the ridge that strengthens south of Mada (the displacement of the system limiting the negative effect of the north flow, and benefiting from a good polar divergence). As it tracks towards the SSO, it remains near the coast of Mozambique , whose proximity could have a limiting effect, but on waters with particularly favourable potential.

The location near or on the land of the low pressure zone should not allow its deepening but rather favour the intensification of the monsoon flow.

This situation should leave at least winds close to 35 knots over a good part of the canal.

Related to this situation, weather conditions will be disturbed during the week on the coastal regions of the Mozambique channel in Madagascar and Mozambique.

The risk that an other moderate tropical storm forms in the Mozambique Channel is low to moderate from Friday onwards and become moderate on Sunday.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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567
AWIO20 FMEE 121235

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/12 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 no029/10 and WTIO30 no29/10/20202021 on tropical cyclone
ARAJI.

Next Warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) pattern axed along 11S east of 50E and towards 15oS east of 70oE. In the Mozambique Channel, the monsoon flow converges to a low-pressure area now located on land over southern Mozambique.

The convective activity in the basin is mainly present near FARAJI for the Indian Ocean part. In the Mozambique Channel, the convective activity is moderate to strong in the southern semicircle of the overland depression. It is strong to locally very strong on a meridian axis located in the channel between 40oE and 45oE between 12S and 22oS.

Severe Tropical Storm FARAJI :

Position at 0930UTC : 18S/81.7E

Estimated minimum pressure: 984 hPa

Max wind over 10 minutes: 60kt

Forward motion: NNW 9kt
For more information, please refer to the next bulletins issued at 12UTC and following.

Over the Mozambique Channel:

The depression with the hybrid characteristics followed since yesterday made landfall over the coast of Mozambique late last night without having managed to develop a sustained and durable convective activity near its center. At 0900 UTC, the circulation, fairly well defined, is centered over land at about 22.1oS and 34.1oE about 230 km northwest of Inhambane.

This low pressure system is expected to remain over land in the southern region of Mozambique for the next 2-3 days near the border with Zimbabwe and South Africa. During this period, fairly heavy rains of up to 50 mm in 24 hours and locally up to 100 mm are expected near the low pressure center and locally on the coastal areas between Inhambane and Maputo in the onshore easterly winds

Next week, the arrival of a South to South-East trade wind surge behind a cold front, will increase the low levels convergence within a Monsoon Trough (MT) pattern which will settle over the southern channel. The current overland depression may move back overseas within this MT or a new low may develop. In spite of the installation of an upper levels ridge, the presence of land, the arrival of dry subtropical air in connection with the trade winds surge, and the lack of consensus within the numerical guida
nce, still leave a low potential of tropical storm formation over the Southern Channel during the first part of the week.

Whatever the scenario, this situation will continue to generate sustained disturbed weather over a large part of the southern channel. The risk of heavy rains and induced flooding is therefore marked for the southern regions of Mozambique as well as some areas of the west coast of Madagascar.

The risk of tropical storm formation becomes low from Monday in the southern part of the Mozambique Channel.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$

s
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429
AWIO20 FMEE 131032

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/13 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 no033/10 and WTIO30 no33/10/20202021 on Moderate Tropical Storm FARAJI.

Next Warnings issued at 12UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:

The basin remains in a monsoon trough (MT) pattern along 11S east of 52E and around 14S east of 67E. In the Mozambique Channel, the monsoon flow converges toward a low-pressure area located overland on southern Mozambique.

Convective activity in the basin is mainly present near FARAJI for the Indian Ocean part, but also to a lesser extent near a low located east of Rodrigues around 21S/67E. In the Mozambique Channel, convective activity is generally strong, in connection with the depression evolving over land on southern Mozambique.

Moderate Tropical Storm FARAJI :
Position at 0900 UTC: 19.4S / 80.0E
Estimated minimum pressure: 997 hPa
Max wind over 10 minutes: 40 kt
Movement: WSW 4 kt
For more information, please refer to the next bulletins issued at 12UTC.

Overland Depression in Southern Mozambique :

At 0900 UTC, the depression is centered over land at about 22.9oS and 34.6oE at a bit more than 100 km northwest of Inhambane.

This depression is expected to station over land in southern Mozambique during the next 2-3 days near the border with Zimbabwe and South Africa. During this period, fairly heavy rains of up to 50 mm in 24 hours and locally up to 100 mm are expected near the low pressure center and locally on the coastal areas between Inhambane and Maputo in the moist easterly sea winds.

Next week, the acceleration of the southerly wind behind a front will increase the convergence of low layers within a Monsoon Trough pattern (MT) which will settle on the South of the channel. It is then not impossible that the low pressure currently on land will return to the sea within this MT where a new minimum will develop. In spite of the development of a upper-troposphere ridge, the presence of land and the lack of consensus within guidances suggest only a low risk of a tropical storm forming on the
South of the Canal by mid-week.

Whatever the scenario, this situation will continue to generate sustained bad weather over a large part of the southern part of the Canal. The risk of heavy rains and induced flooding is therefore marked for the southern regions of Mozambique as well as some areas of the west coast of Madagascar.

The risk of tropical storm formation becomes low from Tuesday in the southern part of the Mozambique Channel.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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969
AWIO20 FMEE 140954

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/14 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (TM) configuration oriented towards 9S/52E and towards 14S/76E. In the Mozambique Channel, the monsoon flow continues to converge towards a low-pressure area located over land in southern Mozambique, at about 22.8S/32.2E. Convective activity in the basin is mainly present in the central part of the Mozambique Channel in conjunction with the overland depression in Mozambique. FARAJI still shows moderate convective activity in the southeast quadrant of its circulation.

Filling Depression FARAJI :
Position at 0900 UTC: 20.5S / 76.9E
Estimated minimum pressure: 1005hPa
Max wind over 10 min : 30kt
Displacement: OSO 8 kt

Depression over land in southern Mozambique:

At 0900 UTC, the depression is centered on land around 22.8S/32.2E. This depression is expected to station over land in the Southern region of Mozambique during the next 2 days. During this period, the southerly wind behind a front will increase and will continue to generate disturbed weather over a large part of the southern region of the channel. Thereafter, it is then not impossible that the depression currently over land will return to the sea and may define a potential cyclogenesis, the risk of which r
emains low, however.

The risk of formation of a tropical storm remains low from Thursday in the southern part of the Mozambique Channel.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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499
AWIO20 FMEE 151134

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/15 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) pattern oriented towards 10.5S/67E and 8.9S/89.5E. The monsoon flow takes a predominant zonal component north of the MT, near 3S, East of 72E.

Over the Mozambique Channel the monsoon flow keeps converging towards an overland depression located since the end of last week in Southern Mozambique.

The convective activity is mainly located in the northern part of the MT, in the slowdown area of the monsoon flow, as well as in the central part of the Mozambique Channel in connection with the overland depression in Mozambique.

Filling Depression FARAJI :
Position at 0930 UTC: 19.5S / 72.3E
Estimated minimum pressure: 1008hPa
Max wind over 10 min: 25kt in the southern semicircle, by gradient effect. Current movement : ONO 11 kt.

Overland depression in the South of Mozambique:

At 0930 UTC, the overland depression is centered around 22.1oS and 33.4oE. This low is expected to remain over land in the Southern region of Mozambique until tomorrow. On Tuesday, the southerly wind behind a front will progress towards the South of Mozambique and will supply moisture to the low pressure system already in place. This will contribute to generate disturbed weather, including heavy rains (50 to 100 mm/12h) over a large part of the southern region of the channel and until the end of the period.
In the medium range, it is likely that the overland depression will return on sea, and may define a potential cyclogenesis. The risk is moderate for the moment.

Development of a moderate tropical storm over the southern part of the channel is moderate from Wednesday onwards.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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011
AWIO20 FMEE 101054

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/10 AT 1200 UTC

PART 1:

WARNING SUMMARY:


PART 2 :
TROPICAL WEATHER DISCUSSION:

The monsoon flow is established over the entire width of the basin and preferentially west of 75E where it feeds a broad southeast/northwest facing between 20oS/53oE and 9oS/90oE. At the extreme west of this trough, the remnant low DANILO drifts to the east of the Mascarene archipelago.

Remnant low 06 (DANILO) :

Position at 0900UTC : 18.9oS/60.0oE

Maximum wind over 10 minutes: 25 kt

Estimated central pressure: 1003 hPa

Current movement: West-Southwest 8 kt

For more information please refer to bulletins WTIO21 and WTIO31 issued at 06 UTC and following.

East of the basin:

With the reconstruction of the monsoon trough on the eastern part of the basin, in an environment where the vorticity of low layers is supported by a low frequency signal and where the monsoon flow is strongly modulated by multiple wave activity (Equatorial Rossby/MRG/...), several areas are under
urveillance.

In the Australian area, a vortex is followed by the Tropical Cyclone Outlook for the Western Region, south-southwest of the Cocos Islands. This minimum is noticed on the last visible images around 18S/94E.

Also, on the extreme Northeast of the basin, a low layer clockwise circulation, quite elongated, is visible at 0900Z, around 10oS/86.7oE.

These two minima do not present any risk of cyclogenesis in the short term, notably due to the current weak lower Level convergence on the equatorial side. However, at the end of the period, with the strengthening convergence of the monsoon flow, a minimum could form under the high ridge, to the northeast of the basin. Deterministic and ensemble models agree enough on this scenario to suggest a risk of cyclogenesis in the long term.

Over the next 5 days, the risk of another moderate tropical storm formation becomes low from Thursday onwards.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
x
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173
AWIO20 FMEE 111048

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/11 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 FMEE no45/6 and WTIO30 FMEE no44/6/20202021 issued on remnant low 06 (DANILO) at 06UTC.

Next warnings for only WTIO30 FMEE at 12UTC.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin presents a monsoon trough (MT) configuration centered between 6oS/55oE and 11oS at the eastern end of the basin. The convective activity is moderate to strong on the northern face of this MT but also close to the African coast at the level of the monsoon flow on the northern part of the Mozambique Channel. At the eastern edge of the basin, a large low-pressure area defines the end of the MT where convective activity is strong. Further south of this zone, convective activity is also noticeable in t
he eastern sector of a low pressure circulation followed by the Tropical Cyclone Outlook for the Western Region of the Australian Basin yesterday.

Residual Depression 06 (DANILO) :

Position at 0900UTC: 19.7oS/57.9oE

Maximum wind over 10 minutes: 20 kt

Estimated central pressure: 1006 hPa

Current movement : West-South-West 6 kt

For more information refer to bulletins WTIO20 and WTIO30 issued at 06 UTC and following for WTIO30.

Low level clockwise circulation East of the basin:

Position at 0900UTC: 19.5oS/86.1oE

Maximum wind over 10 minutes: 30 kt

Estimated central pressure: 1007 hPa

Current movement : West 20 kt

Yesterday, in the Australian zone, the minimum is now in the South-West Indian Ocean basin under the responsibility of the RSMC of Reunion Island. This circulation presents winds of about 30kt in the South sector (locally 35kt due to gradient effect and rapid movement). This circulation evolves in a sheared environment which will not allow it to remain more than 24 hours.

Large low-level clokcwise circulation to the East of the basin:

A low-level clockwise circulation, quite elongated, is visible at 0900UTC, around 11.5oS/87.3oE. The partial ASCAT swath of 0339UTC provides maximum winds of about 20kt. In an environment that will evolve favorably (strengthening of the monsoon flow and wind shear remaining low), deterministic and ensemble models agree enough on this scenario to propose a risk of cyclogenesis in the long term.

Over the next 5 days, the risk of another moderate tropical storm formation becomes moderate from Friday onwards.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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184
AWIO20 FMEE 131222

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/01/13 AT 1200 UTC

PART 1:

WARNING SUMMARY:


PART 2 :
TROPICAL WEATHER DISCUSSION:

The basin is currently in a Monsoon Trough (MT) pattern, East of 65oE. On the East side of the basin, the flow at the Equator becomes westerly under the influence of multiple wave activity (propagation of a Rossby Equatorial wave / low frequency wave and MJO wave). The passage of the Rossby Equatorial wave has notably contributed to trigger the formation of two cyclonic gyres on both sides of the Equator. South of the Equator, the one located in our AoR, is nested within the MT and has a significant cyclogenesis potential (see below).

West of 65oE, the convective activity is weak and is concentrated in the slowing down of the monsoon flow, especially northeast of Cap d'Ambre, as well as along the northwest coast of Madagascar, between Mayotte and Madagascar, subject to the diurnal cycle.

The residual depression DANILO, dissipated last night northwest of Reunion Island.

Depression circulation east of Rodrigues Island:

Position at 0900UTC: 19.6S/68.9E

Maximum wind over 10 minutes: 15kt

Estimated central pressure: 1009 hPa

Current movement: West 21 kt

With strong westerly shear aloft and middle-level dry air, the circulation is now dissipating.

Broad low level clockwise circulation southeast of the Chagos archipelago: Position at 0900UTC : 13S/79E
Maximum wind over 10 minutes: 25kt
Estimated central pressure: 1002 hPa
Current movement: West-Southwest 17 kt

The partial ScatSat-1 swath of this morning, showed a poorly defined and fairly elongated low pressure circulation in an East-West axis. Over the next few days, this low level circulation will encounter environmental conditions moderately favorable for its development. The convergence of low layers on the polar side will strengthen. Upper environmental conditions will be conducive, at the northern margin of the high ridge, with the absence of dry air aloft and moderate wind-shear in the Eastern sector. From
Friday onwards, the upper level divergence will set up on the equatorial side of the system. The cyclogenesis process could thus take shape in the next few days. All the available guidance (ensemble and deterministic) propose a cyclogenesis in the second half of the week. Initially, the system should move in a general westerly direction on the north face of the subtropical ridge.

A suspicious low is also present within the MT in the Australian' AoR, near from the Cocos Islands. This low-level circulation is expected to encounter mid-level dry and weak wind shear from the East to Northeast. Also, the development of this system should be rather slow at first. Next weekend, it could enter in our basin but encounter weak low level convergence conditions, with poor polar feeding, and an absence of equatorial flow. The mid-level dry air will remain aloft. Only a good upper level divergenc
e could give back strength to this system, in the beginning of next week, in front of a upper trough.

South of the Chagos, the risk of formation of a moderate tropical storm becomes moderate from Thursday and strong Saturday.

Over the extreme East of the basin, the risk of formation of a moderate tropical storm becomes low from Saturday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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902
AWIO20 FMEE 251233

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/25 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Monsoon Trough (MT) pattern centered between 12S and 15S. For the time being, the vorticity areas present within this MT remain sufficiently weak not to generate a significant cyclogenesis risk at short range, in northern Madagascar and east of Agalega. In the Australian area of responsibility , a tropical depression is monitored by the BOM, and could enter in our area of responsibility next week.

North of the Mozambique Channel :

A weak clockwise circulation is currently present near the northern tip of Madagascar around 11.7S / 49.3E at 10Z. Convective activity is weak and intermittent near this low, with maximum winds close to 15kt in the monsoon feeding.

This weekend, the strengthening of low level westerly winds under the likely impulse from a Kelvin wave should favour the increase of convective activity and the deepening of the low pressure system. Numerical models similarly suggest the formation of an area of disturbed weather moving southwestward from Sunday. Despite good surface feeding on the northern and southern sides, the proximity to the land should significantly limit the risk of significant deepening.

The risk of formation of a moderate tropical storm in the Mozambique Channel becomes low on Tuesday.

In the center of the basin :

On the edge of the TM, south of Diego-Garcia, a low could isolate early next week, mostly thanks to the strengthening of the upper divergence on the polar side near an upper trough. In a partially favorable environment, possibly hindered by the presence of Australian system,a cyclogenesis is possible. Its potential depends on the track and intensity of the neighboring system.

The risk of formation of a moderate tropical storm in the center of the basin becomes very low on Tuesday.

In the Australian AoR :

The tropical depression monitored by the BOM in its IDW27600 warnings, could approach our area of responsibility and possibly cross 90E early next week according to the last run of the EPS. The latest official TCWC forecast still places the system east of 90E on Tuesday morning. Its entry in our area is still rather uncertain because of a possible change of trajectory which would occur on Tuesday according to most of the numerical guidances.

Chances for the entry of a tropical storm or cyclone by the eastern border are moderate on Tuesday

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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350
AWIO20 FMEE 261212

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/26 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) pattern. This MT undulates eastwards from 50E between 11S and 14S.

The convective activity is located on the equatorial side of the MT, in the slowing down area of the monsoon flow, the north of the Mozambique Channel, as well as around 2 vortex: one located at the northern tip of Madagascar, and a second one south-east of Agalega archipelago. It is quite tricky to follow these small localized low with conventional satellite imagery, as they remain poorly marked in terms of visual signature; the Total Precipitation Water animation CIMMS product, helps us greatly in this ta
sk. These low do not constitute a sufficient potential for cyclogenesis in the short term. On the other hand, the Tropical Cyclone MARIAN located in Australian's AoR, south of the Cocos Islands, and followed by the BOM, could soon enter our area of responsibility early next week.

Northern tip of Madagascar :

A very weak and wide low pressure circulation is located near the North-Eastern tip of Madagascar with an ill-defined center. The 0630Z ASCAT-B swath indicates maximum winds speed of 15 kt, located in the south of the low layer circulation, under the flouring convection, in the feed of the trade winds.

On Sunday, under the effect of a favorable wave activity (Kelvin wave associated with a Rosby wave) the monsoon flow strengthens over the north of the channel by taking a more zonal direction. In spite of a weak polar flow, this westerly thrust should momentarily favor convective activity in a warm and humid low layer air mass and thus lead to dig an area of low presure. However, the latest guidance are mixed on this scenario. The deepening of this vortex seems difficult to develop, probably due to a lack o
f low level convergence (on both side) that seem to be struggling to converge. The proximity of the land seems to be a limiting factor for the development of this low.
Thus, the risk of formation of a moderate tropical storm in the Mozambique Channel becomes low from Tuesday onwards.

In the center of the basin, south-east of Agalega archipelago:

On the edge of the MT south-east of Agalega achipelago, a vorticity area can be seen on the CIMMS analysis. The 0330Z ScatSat-1 swath shows two fairly close low layer centers, hence defining an elongated and poorly defined low layer circulation, with maximum mean winds of about 25kt by gradient effect in the southern semicircle. This low pressure circulation will benefit from mixed environmental conditions: the low level convergence on the equatorial side will strengthen from the end of this weekend. The tr
ade winds will converge and strengthen at the beginning of next week, associated with a good upper divergence at the front of a trough. Only the mid-level wind shear could hamper the general dynamics. In this context, a cyclogenesis is possible.However, the numerical models diverge for the moment on the timing (IFS remains more reactive than GFS).
The risk of formation of a moderate tropical storm on the center of the basin becomes low from Tuesday onwards.

In the Australian zone, south of the Cocos Islands :

The Tropical Storm MARIAN was baptized at 0600Z and is currently monitored by the BOM through the IDW10800 bulletins. MARIAN is located at 0900Z by 14.1S 97E, and is moving westwards at 16kt.

According to the latest ensemble and deterministic models, MARIAN should enter our AoR very punctually early next week, before returning to the Australian's AoR on Tuesday/Wednesday, taking a south-easterly track.
Chances for the entry of a tropical storm by the eastern border are important on Tuesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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766
AWIO20 FMEE 271301

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/27 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) pattern. This MT undulates eastwards from 50E between 11S and 14S.

The convective activity is located on the equatorial side of the MT, in the slowing down area of the monsoon flow, the north of the Mozambique Channel, as well as around around an area of low pressure south-east of Agalega
rchipelago.

It is currently possible to identify two cyclogenesis zones in the basin in the medium term: one in the center of the canal and a second one southeast of Algalega.

On the other hand, the Severe Tropical Cyclone MARIAN located in Australian's AoR, south of the Cocos Islands, and followed by the BOM, could soon enter our area of responsibility at the end of the weekend or beginning of next week.

Centrer of the channel :

By mid-week, some models propose a cyclogenesis at the convergence of the South flow already well established on the south of the channel, but weakening with the strengthening of the monsoon flow on the north of the channel. A very weak and wide low pressure circulation develops in the models on the center of the channel. The environment seems favorable in altitude, and improves even at the end of the period as the thalweg approaches.

However, the latest guidelines are mixed in the scenario to be adopted. The deepening of the depression seems difficult to develop, surely due to the lack of feeding by the convergence of the low layer flows that do not establish themselves at the same time. The proximity of the land also seems to be a limiting factor for the development of this system.

Thus, the risk of formation of a moderate tropical storm in the Mozambique Channel becomes low from Thursday onwards.

In the centrer of the basin, south-east of Agalega archipelago:

On the edge of the TM south-east of Agalega, a zone of vorticity can be detected on the CIMMS analyses, as well as on the satellite animation.

Passes HY-2b of 0130Z and ScatSat-1 of 0430Z identify a very weak closed circulation around 12.5S/61E.

This low pressure circulation will benefit from mixed environmental conditions: the convergence of low layers on the equatorial side will strengthen from the end of this weekend, while it will be necessary to wait until Wednesday to see the convergence improve on the polar coast. The divergence of altitude is good under the axis of the ridge, in front of the thalweg, but the middle tropopause environment is dry, and from Tuesday a middle tropopause shear should advect the dry air without the system.

In this context, a deepening at the storm stage is possible in the medium term, confirmed by the IFS ensemble forecast.
The risk of formation of a moderate tropical storm on the center of the basin becomes low from Tuesday onwards.

In the Australian zone, south of the Cocos Islands :

The strong tropical storm MARIAN is currently being tracked by the BOM through the IDW27600 bulletins. MARIAN is located at 0900Z by 16.0S 97.7E, and is moving southwest to west at 9kt.

According to the latest ensemble and deterministic models, MARIAN should enter our area of responsibility very punctually at the end of the weekend or early next week, before returning to the Australian zone on Tuesday/Wednesday, taking a south-eastbound course.
Chances for the entry of a tropical storm by the eastern border are important on Tuesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
n

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274
AWIO20 FMEE 281155

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/02/28 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) pattern along 13S. Convection is mainly located along the axis of the MT as well as equatorward in the slowing monsoon flow and on the center of the Mozambique Channel. East of the basin, tropical cyclone MARIAN will temporarily track West of 90E.

Center of the Mozambique channel :

Fueled by monsoon flow northward and a southerly burst, a vorticity area is expected to develop early next week over the central part of the Mozambique Channel, off the St Andre cape. The upper conditions are expected to remain conducive for tropical development until Thursday night and the arrival of a north-westerly shear ahead of a mid-latitudes upper trough. On the other hand, the proximity of land and the large initial vorticity area seem to make the building of a concentrated convective core difficult
. However, the 00Z IFS run is more reactive today, and the cyclogenesis signal is increasing within the available ensemble prediction.

Thus, the risk of formation of a moderate tropical storm in the Mozambique Channel becomes moderate from Thursday.

In the center of the basin, south-east of Agalega archipelago:

A low/mid-level vorticity area is still nested within the MT, with sat animations suggesting a surface circulation center near 12.9S/59.4E at 09Z. This morning ASCAT swath show an elongated circulation with 15/20-kt max winds still rather far away from the center. The upper divergence is excellent equatorward and expected to improve poleward from Tuesday. A lack of poleward low-level convergence should slow the cyclogenesis down, while a mid-level northwesterly shear could bring dry air over the center from
Wednesday. The main available guidance is not in a good agreement over the cyclogenesis risk.

The risk of formation of a moderate tropical storm South-East of Agalega becomes low from Tuesday and moderate from Thursday.

Tropical Cyclone MARIAN :

MARIAN is currently monitored by the Australian TCWC and currently at the tropical cyclone stage (severe tropical cyclone in terms of Australian classification). The cyclone will temporarily enter the RSMC area of responsability but is expected to quickly turn Southeastward tomorrow and rapidly cross again the basin border. Thus, it has been decided that the BoM TCWC will continue to issue the warnings concerning this system even during its short passage West of 90E.

Please refer to the technical bulletin IDW27600 issued by BoM and followings for more informations.

MARIAN will temporarily track West of 90Z while remaining under Australian supervision.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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536
AWIO20 FMEE 011004

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/01 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) configuration positioned around 10S to the west of the basin and around 16S to the east. Moderate to strong convection is localized on the axis of this MT as well as in the center of the Mozambique Channel and at the eastern end of the basin, at the level of tropical cyclone MARIAN positioned at the limits with the Australian basin.

Center of the Mozambique channel :

In spite of the continued monsoon flow to the North and the surge of wind from the South, the ASCAT swath of 0544UTC shows an ill-defined circulation around 15.4S/42.8E. In this area, convective activity is expected to continue and although altitude conditions remain favorable for the development of a tropical system, consolidation of the low-level circulation will take time. The system is expected to remain below the threshold of a moderate tropical storm before landing on the west coast of Madagascar.

Thus, the risk of formation of a moderate tropical storm in the Mozambique Channel is low until Friday, before landing.

In the center of the basin, south-east of Agalega archipelago:

The partial ASCAT swaths of 0402UTC and 0517UTC only allow to locate a large circulation in this area, around 13.2S/61.4E, within the MT. The lack of convergence of low layers on the polar side continues to affect the cyclogenesis process. However, the main available models continue to present this zone as a potential area for cyclogenesis with an intensification that remains limited, due to the degradation of environmental conditions during the week (dry air at the southern and western edge of the system).


The risk of formation of a moderate tropical storm South-East of Agalega becomes moderate from Thursday onwards.

Tropical Cyclone MARIAN :

Although it is expected to enter the South-West Indian Ocean basin very soon, cyclone MARIAN, located at 06UTC by 17.9S/90.0E, continues to be monitored by the specialized cyclone center of Perth through the BoM IDW27600 technical bulletins. Due to its temporary displacement (nearly 24 hours) over our basin but at a longitude remaining close to 90E, the monitoring of this system remains under the responsibility of the Perth center.

MARIAN will temporarily track West of 90E while remaining under Australian supervision.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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986
AWIO20 FMEE 021233

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/02 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) pattern. The MT is undulating between 11 and 19S, punctuated by three well-identified cyclonic vorticity areas around which most of the basin's strong convective activity is focused : from west to east, a low in the Mozambique Channel around 18S/40E, a circulation in the center of the basin near 14S/63E and finally Tropical Cyclone MARIAN located around 19S/90E, on the boundary with the Australian area of responsibility.

From the Mozambique Channel to the southeast of Madagascar :

The latest satellite images now clearly show a closed cyclonic circulation off the coast of Mozambique around 18S/40E, linked to the improved low-level convergence between the monsoon flow and a surge of southeasterly trade winds south of the Mozambique Channel. Convection nevertheless remains scattered quite far around this low pressure center, especially in the slowing down of the monsoon flow both near the Comoros and the trade winds on the south of the Channel. In the coming days, although altitude cond
itions remain favorable for development of a tropical system, full consolidation of the low-level circulation should take time. Nevertheless, there remains just enough time for this system to reach the threshold of a moderate tropical storm before landfall on the west coast of Madagascar around Friday. Even if the system only reaches the stage of a tropical low, heavy rainfall is likely on the western parts of Madagascar.

On Saturday, under the influence of a west-northwest steering flow, most models expect this circulation to emerge or reform in the Indian Ocean east or southeast of Madagascar, encountering then mixed environmental conditions. Advection of moist low level air on the equatorial side, good upper divergence on the polar side and a significant oceanic potential are favourable ingredients for storm development. Nevertheless, other factors seem to work against cyclogenesis, namely a probably insufficient surface
convergence on the polar side of the low and the presence of moderate northwesterly vertical shear advecting dry air in the mid-troposphere along the edge of the subtropical jet stream. Ensemble and deterministic guidance show a still quite marked dispersion in terms of trajectory and intensity of this system.

The risk of formation of a moderate tropical storm in the Mozambique Channel is considered low on Thursday and moderate on Friday, before landfall over western Madagascar. After a brief track overland, the risk that this system will strengthen into a tropical storm off southeast Madagascar is considered low from Saturday.

In the center of the basin :

North of Rodrigues, around 14S/63E, we note an improvement since yesterday of the convergence between the monsoon flow and the trade winds. The low-level circulation remains still quite elongated but convection has intensified since yesterday and is more concentrated around the circulation. Main available models suggest that good surface convergence should persist through the weekend. With largely sufficient oceanic potential and good upper divergence, this suggests a potential for cyclogenesis by Thursday
or Friday. Until then, the system should drift east-southeastward under the influence of the low and mid-troposphere steering flows, thus tracking on Friday between 70 and 80E and between 15 and 18S, far from inhabited land. Nevertheless, a gradual increase in deep west to northwesterly shear and dry air advection along the western boundary of the system are noted as limiting factors. Various models diverge on the intensification of this system (GFS is much more reactive th
an IFS,
in particular).

The risk of formation of a moderate tropical storm over the center of the basin becomes moderate from Thursday onwards.

Tropical Cyclone MARIAN :

Tropical Cyclone MARIAN continues to be monitored by the Perth Tropical Cyclone Center via the BoM's Technical Bulletins IDW60281, despite its brief incursion in our basin between yesterday (Monday) and today (Tuesday) at a longitude remaining close to 90E. This system, which is expected to be around 18.7S and 89.9E at 12UTC this Tuesday according to the BoM, will move back into the Australian AOR east of 90E by tomorrow (Wednesday).

MARIAN, remaining under Australian supervision, is about to complete its brief incursion in our basin and will move back east of 90E by Wednesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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515
AWIO20 FMEE 031149

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/03 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) pattern. The MT is undulating between 8S and 17S, punctuated by three well-identified cyclonic vorticity areas around which most of the basin's strong convective activity is focused : from west to east, a depression in the Mozambique Channel around 18S/39E, a circulation in the center of the basin near 14S/65E and finally the severe tropical storm MARIAN located around 19S/91E, on the boundary of the Australian area of responsibility.

From the Mozambique Channel to the southeast of Madagascar :

The latest satellite images now clearly show a closed cyclonic circulation off the coast of Mozambique, confirmed by the ASCAT-C pass of 0730utc. The center is located near around 18S/39S, with winds about 10/15kt.

Despite of a good divergence in altitude, the system is really fed only by the strengthening of the monsoon flow on the North of the channel. The lack of polar convergence, and the arrival of dry air in mid tropopause by the West on Friday, should limit the chances of development before its landing on the Malagasy West coast, on Friday.

Even if the system only reaches the stage of a tropical depression, heavy rainfall is likely on the Mozambique coast and the center of the channel today and Thursday, then Friday over the western regions of Madagascar.

On Saturday, under the influence of a west/northwest steering flow, most models expect this circulation to emerge or reform in the Indian Ocean east or southeast of Madagascar, encountering then mixed environmental conditions. The advection of humid low layer air on the equatorial side, a good polar altitude divergence and a consequent oceanic potential are favourable ingredients for storm development.

Nevertheless, other factors seem to work against cyclogenesis, namely a probably insufficient surface convergence on the polar side and the presence of moderate northwestern vertical shear advecting dry air in the middle troposphere at the edge of the subtropical jet stream. The ensemble and deterministic models show a still quite marked dispersion in terms of trajectory and intensity of this system.

The risk of formation of a moderate tropical storm in the Mozambique Channel is considered low on Thursday and Friday, before landfall over western Madagascar. After a brief track overland, the risk that this system will strengthen into a tropical storm off southwest Mascareignes islands is considered low to moderate from Sunday.

In the center of the basin :

North of Rodrigues, around 14S/65E, there has been an improvement since yesterday in the convergence between the monsoon flow and the trade winds, resulting in a better organization of convection. The circulation of low layers has also improved, and the last ASCAT-C pass of 0530UTC, show winds of the order of 15/20kt.

Main available models suggest that good surface convergence should persist through the weekend. With largely sufficient oceanic potential and good upper divergence, this suggests a potential for cyclogenesis by Thursday or Friday. Until then, the system should drift east-southeastward under the influence of the low and mid-troposphere steering flows, far from inhabited land.

Nevertheless, a gradual increase in deep west to northwesterly shear, the effect of which will be limited initially by the movement of the system in the same direction as the shear, and dry air advection along the western boundary of the system are noted as limiting factors. Various models diverge on the intensification of this system(IFS is more reactive than GFS and UKMO, in particular).

The risk of formation of a moderate tropical storm over the center of the basin becomes high from Thursday onwards.

Severe Tropical Storm MARIAN :

The system was returned to the Australian domain at the end of Tuesday and continues to be monitored by the Perth Cyclone Specialist Cyclone Center through BoM Technical Bulletins IDW27600.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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362
AWIO20 FMEE 041009

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/04 AT 1200 UTC

PART 1:

WARNING SUMMARY:

Warnings WTIO20 and WTIO30 no 03/13/20202021 issued on Tropical Depression 13-20202021 at 06UTC.

Next warnings issued at 12UTC.

Warnings concerning the area of disturbed weather 14-20202021 will be issued at 12UTC.

PART 2 :
TROPICAL WEATHER DISCUSSION:

The basin is in a monsoon trough (MT) pattern on its entire width. Convection is mainly concentrating around the two systems monitored by the RSMC : tropical depression 13 on the center of the basin and an area of disturbed weather numbered 14 on the center of the Mozambique Channel.

Tropical Depression 13-20202021 :
Position at 09UTC : 16.1S/71.7E
Max 10-mn wind : 30 kt
Motion : East-South-Eastward at 15kt
Estimated central pressure : 998 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and followings.

This system is expected to intensify until Friday evening. No threat for inhabited islands.

Area of disturbed weather 14-20202021 :
Position at 09UTC : 16.3S/41E
Max 10-mn wind : 20 kt
Motion : East-North-Eastward at 10kt
Estimated central pressure : 1003 hPa
For more information about this system, please refer to bulletins that will be issued at 12UTC and followings.

This weak system will bring heavy rainfall on the western Madagascan coast tonight and inland tomorrow as it will cross Madagascar. Over the week-end, the low may come back over sea and track South of the great Mascarenes at a distance that remains to be determined. Associated thunderstorms and heavy rainfall are likely to affect Reunion and Mauritius islands.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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564
AWIO20 FMEE 051031

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/05 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 07/13/20202021 issued on Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.

Warnings WTIO24 and WTIO30 no 04/14/20202021 issued on Tropical Depression 14-20202021 at 06UTC.

Next warnings issued at 12UTC.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in monsoon trough (MT) configuration over its entire width. The convective activity is mainly concentrated around the two systems monitored by the RSMC, recalled below, and more anecdotally in the weakly low-pressure area off the east coast of Madagascar around 19S/52E, due to flow convergence
ffect.

Tropical Cyclone HABANA :
Position at 09UTC : 16.4S/76.0E
Max 10-mn wind : 80 kt
Motion : East-North-Eastward at 6kt
Estimated central pressure : 970 hPa

For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and followings.

Tropical Depression 14-20202021 :
Position at 09UTC : 17.7S/43.9E
Max 10-mn wind : 30 kt
Motion : East-South-Eastward at 12kt
Estimated central pressure : 998 hPa

For more information about this system, please refer to bulletins WTIO24 and WTIO30 issued at 06UTC and followings.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$

s

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779
AWIO20 FMEE 060926

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/06 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 11/13/20202021 issued on Intense Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.

Warnings WTIO24 no 06/14/20202021 and WTIO30 no 08/14/20202021 issued on Zone of Disturbed Weather 14-20202021 at 06UTC.

Next warnings issued at 12UTC.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) configuration over its entire width. The convective activity is mainly concentrated around the intense tropical cyclone HABANA. Two other zones of moderate to strong convective activity are notable north of the Mozambique Channel in the zone of convergence of the monsoon flow and the southern flow up the channel and near the zone of disturbed weather 14-202021 between Madagascar and Reunion Island.

Intense Tropical Cyclone HABANA :
Position at 09UTC : 16.2S/78.1E
Max 10-mn wind : 110 kt
Motion : East-South-Eastward at 4kt
Estimated central pressure : 939 hPa

For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and followings.

Zone of Disturbed Weather 14-20202021 :
Position at 09UTC : 20.0S/49.9E
Max 10-mn wind : 25 kt
Motion : East-South-Eastward at 14kt
Estimated central pressure : 1002 hPa

For more information about this system, please refer to bulletins WTIO24 and WTIO30 issued at 06UTC and followings.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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457
AWIO20 FMEE 071231

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/07 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 11/13/20202021 issued on Intense Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.

Warnings WTIO24 no 06/14/20202021 and WTIO30 no 08/14/20202021 issued on Moderate Tropical Storm IMAN at 06UTC.

Next warnings issued at 12UTC.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a monsoon trough (MT) pattern over its entire width. Convective activity is mainly concentrated around intense tropical cyclone HABANA and moderate tropical storm IMAN. One other area of convection can be observed in the north of the Mozambique Channel to the immediate south of Comoros where the monsoon flow converges with the southern flow established in the Channel.

Intense Tropical Cyclone HABANA :
Position at 09UTC : 17.0S/80.1E
Max 10-mn wind : 95 kt
Motion : East-South-Eastward at 7kt
Estimated central pressure : 952 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

Moderate Tropical Storm IMAN :
Position at 09UTC : 23.3S/56.0E
Max 10-mn wind : 35 kt
Motion : South-Eastward at 13kt
Estimated central pressure : 996 hPa
For more information about this system, please refer to bulletins WTIO22 and WTIO30 issued at 06UTC and following.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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720
AWIO20 FMEE 081042

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/08 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 19/13/20202021 issued on Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.

Warnings WTIO22 no 14/14/20202021 and WTIO30 no 16/14/20202021 issued on post-tropical depression IMAN at 06UTC.

Next warnings issued at 12UTC.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in monsoon trough (MT) pattern over its entire width. The convective activity is mainly concentrated around the tropical cyclone HABANA and the post-tropical depression IMAN. Another zone of moderate convective activity is observed north of a line Tromelin / Saint-Brandon, in an area of low level convergence between the monsoon flow and the west-southwesterly flow generated indirectly by the presence of Iman located south-east of the Mascarene Islands.

Intense Tropical Cyclone HABANA :
Position at 09UTC : 18.3S/81.0E
Max 10-mn wind : 70 kt
Motion : quasi stationnary
Estimated central pressure : 976 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

Moderate Tropical Storm IMAN :
Position at 09UTC : 27.8S/61.2E
Max 10-mn wind : 35 kt
Motion : South-East at 17kt
Estimated central pressure : 996 hPa
For more information about this system, please refer to bulletins WTIO22 and WTIO30 issued at 06UTC and following.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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147
AWIO20 FMEE 091201

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/09 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 23/13/20202021 issued on Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The trans-equatorial flow is established west of 60oE. It feeds an undulating westerly flow established between 10S and 15S over the entire width of the basin. The main convective activity of the basin is located around tropical cyclone HABANA as well as near a zone of persistent convection present in the North of the Mascarene Islands between Agalega and Tromelin.

Tropical Cyclone HABANA :
Position at 09UTC : 18.4S / 79.2E
Max 10-mn wind : 70 kt
Motion : Westwards at 06 kt
Estimated central pressure : 973 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

Filling-up low EX-IMAN :
Position at 09UTC : 29S / 65.5E
Max 10-mn wind : 30 kt
Motion : East-South-East at 9 kt
Estimated central pressure : 1003 hPa

This system will evolve slowly on a track gradually moving more towards the Southeast without any potential for re-intensification either by tropical or baroclinic mechanisms. A definitive dissipation should take place over the next 3 days.

Area of low pressure between Agalega and Tromelin:

Sustained convective activity has been maintained in this sector over the last 24 hours (between 50E and 60E and between 10S and 15S) without however any signs of curvature. The morning ASCAT passes show no closed circulation and pressure observations show a tendency for the pressure field to increase. In spite of a context that could be favorable especially at altitude with an equatorial divergence reinforced by the passage of a Kelvin wave, the low levels convergence will remain poor in a large southeast
ern sector of the zone due to the presence of a low levels trough linked to EX-IMAN and then in a second time with the approach of cyclone HABANA.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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926
AWIO20 FMEE 100949

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/10 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 27/13/20202021 issued on Intense Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The trans-equatorial flow is established over the entire width of the basin and supplies the monsoon trough (MT) centered between 10S and 13S. The convective activity is mainly located near the intense tropical cyclone HABANA. Moderate convective activity can also be noted in the northern part of the Mozambique Channel and more sporadically on the equatorial side of the MT.

Intense Tropical Cyclone HABANA :
Position at 09UTC : 17.5S / 76.4E
Max 10-mn wind : 110 kt
Motion : Westwards at 08 kt
Estimated central pressure : 945 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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335
AWIO20 FMEE 111132

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/11 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 31/13/20202021 issued on Intense Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The trans-equatorial flow is weakly established over the entire width of the basin and supplies the monsoon trough (MT) centered along 14S. The convective activity is mainly located near the intense tropical cyclone HABANA. Elsewhere it is weak.

Intense Tropical Cyclone HABANA :
Position at 09UTC : 17.7S / 74.0E
Max 10-mn wind : 105 kt
Motion : West-south-westwards at 06 kt
Estimated central pressure : 944 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

In the Australian AoR :

East of 90E, a low is monitored by the BOM, located this morning south-south-west of Christmas Island. Late this week-end or early next week, in a poorly conducive environment this low may intensify and enter our AoR. However the risk for the entry of a moderate tropical storm is still not significant.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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511
AWIO20 FMEE 131106

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/13 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 39/13/20202021 issued on Intense Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The large-scale context is changing over the basin: a weak trans-equatorial flow is still established between 50oE and 70oE but it should gradually become less established over the next few days. It feeds a poorly defined Monsoon Trough (MT) oriented North-West / South-East between 10oS and 15oS. Further east, a Near Equatorial Trough (NET) is also poorly defined and is developing around 10oS east of 85oE. The convective activity is mainly located near tropical cyclone HABANA. Other areas of weaker activity
are still observable in the decelerating monsoon flow north of HABANA, as well as south of a weak low-level clockwise circulation present off the northeast coast of Madagascar within the MT. This sector still has no potential for cyclogenesis in this context of gradual weakening of the monsoon flow.

Tropical Cyclone HABANA :
Position at 09UTC : 20.9S/70.3E
Max 10-mn wind : 85 kt
Motion : South-South-westwards at 05 kt
Estimated central pressure : 960 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

In the Australian AOR:

A weak low-pressure area is located near 16oS and 100.5oE, well southwest of Christmas Island (monitored by the BOM through bulletin IDW10800). According to the latest available guidance, there is still no significant risk that this system will become a tropical storm by entering our basin early next week.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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756
AWIO20 FMEE 141117

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/14 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 43/13/20202021 issued on Tropical Cyclone HABANA at 06UTC.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The monsoon flow continues its weakening on the basin. A more and more ill-defined monsoon trough (MT) pattern remains located between 50E and 70E near 15S. Significant deep convection is mainly located North of the Comoros archipelago, North-West of the Mascarenes within the Western extremity of the MT and around HABANA. Furthermore, a near-equatorial trough is gradually emerging on the Eastern part of the basin.

Severe Tropical Storm HABANA :
Position at 09UTC : 22S/70.5E
Max 10-mn wind : 60 kt
Motion : South-Eastwards at 3 kt
Estimated central pressure : 960 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

North-West of the Mascarenes :

Strong convection is currently triggering within the slowing area of the trade winds, off the Madagascan coasts. However, no significant signs of a closed surface circulation have been found on sat animations or available ground obs. Over the next days, environmental conditions are unconducive for the formation of a tropical system in the area, with no equatorward convergence and an Easterly shear aloft.

In the Australian AOR:

A weak low-pressure area is located near 15S/97.5E, far south of the Cocos Islands (monitored by the BOM through bulletin IDW10800). According to the latest available guidance, a lack of equatorward low-level convergence and dry mid-level conditions should prevent any significant deepening. Thus, there is still no significant risk that this system will become a tropical storm while entering our basin early next week.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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323
AWIO20 FMEE 151053

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/15 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 47/13/20202021 issued on Strong Tropical Storm HABANA at 06UTC.

Next warnings issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The monsoon flow continues its weakening trend on the basin, with an ill-defined remnant monsoon trough (MT) located between 50E and 70E near 15S. On the southwestern edge of this MT, an area of deep convection can be found between eastern Madagascar and the western Mascarene islands. Further away to its south-east, weakening Tropical Storm HABANA concentrates its own part of deep convection (see characteristics below).

Furthermore, on the northeastern part of the basin, a near-equatorial trough is gradually emerging, with an axis of convection which has formed between 5S and 8S, east of 80E, and extending further east into the Australian area of responsibility, north of the Cocos.

Moderate Tropical Storm HABANA :
Position at 09UTC : 22.7S/71.3E
Max 10-mn wind : 45 kt
Motion : Quasi-stationnary
Estimated central pressure : 988 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

In the next days, environmental conditions don't appear conducive enough for development of a new tropical system : on the one hand, between Madagascar and Mascarene islands, where surface vorticity and convergence will be mainly focused around HABANA's weak remnants ... and on the other hand, in the near-equatorial trough which should slightly deepen and settle east of 70E and near 10S by the end of the week, with unsufficient low level convergence there as well.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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244
AWIO20 FMEE 161024

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/16 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 50/13/20202021 issued on Fillin up HABANA at 06UTC.

Last warnings issued at 06UTC about this system



PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in configuration of a monsoon trough (MT) located around 12S east of 50E. The convective activity is slightly present on the basin and is located mainly in the southeast sector of the filling up HABANA and north of the Mascarene Islands at the level of the Tromelin island around 16S/55E, in the convergence zone of the trade winds and the monsoon flow. Under the influence of the dry phase of the MJO, the convective activity should remain weak to moderate over the basin during the next days.

Filling Up HABANA :
Position at 09UTC : 22.8S/70.1E
Max 10-mn wind : 30 kt, locally 35kt in the SW quadrant
Motion : Eastern-SouthEastern, 5kt
Estimated central pressure : 1001 hPa
For more information about this system, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC.

During the next 5 days, there is no risk of another moderate tropical storm forming in the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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031
AWIO20 FMEE 181122

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/18 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:

As in the past few days, the Monsoon Trough (MT) remains weak. It undulates to the East from 48E to 66E, between 9S and 12S. Over the extreme east of the basin, from 76E, the trans-equatorial flow struggles to impose itself and the basin's pattern looks more like a Near Equatorial Trough (NET) poorly defined between the trade winds and a westerly to southwesterly flow near the equator. The convective activity is also not very significant on the basin and is mainly located in the southwest of the MT between
the north of Madagascar and the north of Tromelin Island, as well as west of the Cap d'Ambre on the northern part of the Mozambique Channel.

Remnant low HABANA :
Position at 0930UTC : 21.6S/69.9E
Max 10 mn wind : 25 kt in the SW quadrant by gradient effect.
Current Movement : WNW 3kt.
Estimated central pressure : 1007 hPa.

Over the next few days, the environmental conditions will remain unconducive for cyclogenesis over the basin. The low level convergence will have some difficulty to set up, because of the monsoon flow which will struggle to enter and strengthen over the north of the basin, despite the presence of a well-established trade wind. In addition, the situation aloft is impacted by a large-scale context, too dry over most of the basin. Consequently, the latest guidance does not suggest any significant signal for th
e emergence of a tropical storm during the next five days.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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412
AWIO20 FMEE 191009

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/19 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a weak monsoon trough (MT) configuration located around 11S east of 50E. Over the extreme east of the basin, from 72E, the trans-equatorial flow is weak and defines a configuration that looks more like a Near Equatorial Trough (NET).

The convective activity over our basin is moderate to strong mainly in the North-East of Madagascar, as well as in the North-East extremity of the basin at the NET.

During the next few days, the environmental conditions will remain unfavorable for cyclogenesis over the basin with a context of dry MJO over the basin and Kelvin waves that focus the convective activity near the equator. Although at the beginning of next week, some guidelines leave the possibility of the arrival in our basin by the eastern edge of a low-pressure circulation, the potential of evolution into a moderate tropical storm remains almost nil during the next five days.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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082
AWIO20 FMEE 201157

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/20 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin displays quite an hybrid pattern, with on the one hand a remnant Monsoon Trough (MT) located from 8S to 12S between 48E and 60E, to the northeast of Madagascar, whereas on the other hand, to the east of 70E the pattern looks more like a Near Equatorial Trough (NET) pattern centered around 9S, with a very much zonal low-level flow close to the equator.

Deep convection over the basin is mainly active to the north/northeast of Madagascar (remnant MT) as well as in the eastern part of the basin, in the vicinity of the NET, some of it within low-level convergence or vorticity areas close to Diego Garcia, but also around a low pressure area near the Cocos islands in the Australian AoR (see outlook IDW10800).

During the next few days, the low pressure area to the north of Madagascar could become better-defined. However, lack of low-level convergence should prevent it from developping into a tropical storm according to current
uidance.

In the eastern part of the basin, environmental conditions could become gradually more conducive within the NET by mid-week, with good tropospheric moisture content and a slight increase in surface convergence, especially on the polar side, as well as low deep-layer shear. Moreover, various large scale equatorial wave patterns (MJO, Kelvin, Rossby) seem to gradually become a bit more conducive for convection enhancement by the end of the forecast period. In this context, some NWP models now suggest that the
low near the Cocos could move into the eastern SWIO basin and develop into a weak storm as from mid-week. This scenario also translates into an increase in probabilities in the latest european ensemble forecast, although the risk remains low and will need further confirmation. Some ensemble model runs also suggest possible development a bit further west, closer to Diego Garcia, but with a lower probability and later occurrence.

The risk of development of a moderate tropical storm becomes low in the eastern part of the basin from Wednesday onwards.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
u
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720
AWIO20 FMEE 211219

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/21 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin displays Near Equatorial Trough (NET) along 7S east of 65E. Convective activity is moderate to strong near the NET especially in the westerlies but also around a low pressure area near the Cocos islands in the Australian AoR (see BoM's outlook IDW10800).

In the australian AoR :

A low is monitored by BoM west of the Cocos islands, located at 06Z near 11.7S/94.6E. Last ASCAT swath show that the surface circulation wasn't closed this morning even if the cloud pattern display a nice rotation currently, at higher levels.

Over the next days, in a temporarily conducive environment, with low shear and excellent upper divergence, this low may deepen and enter our AoR close to the Moderate Tropical Storm stage. Numerical guidance are still quite conservative in their forecast and few members of the American and European EPS, suggest a significant deepening, especially at short range. At longer range, a change in the steering flow may limit the westward track and therefore, make uncertain the entry in our AoR. Given the still num
erous uncertainties, cyclogenesis risk is maintained to low.

The risk of development or entry of a moderate tropical storm in the eastern part of the basin, becomes very low on Tuesday and low from Wednesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
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184
AWIO20 FMEE 231202

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/23 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin displays a Near-Equatorial Trough (NET) pattern along 9S east of 60E. Trans-equatorial flow is currently very weak but could wake up again temporarily in the coming days in the west and central part of the basin.

Moderate to strong convective activity is mainly found within the NET and in some surface convergence areas equatorward, as well as near a vortex located west of the Cocos Islands in the Australian AoR (see BoM's outlook IDW10800).

In the Australian AoR :

A slow-moving low is monitored by the BoM west of the Cocos Islands and was located near 11.8S / 91.2E at 06Z. Various ASCAT swaths this morning have shown a convergent but still quite elongated low-level circulation, with winds reaching 25 to 30 kt in the southern semi-circle, with flaring deep convection displaced to the south of the low-level vortex, which indicates moderate north-to-northwesterly wind shear in the system's environment.

Although poleward inflow should remain good, the NET-related westerly flow to the north of the system doesn't seem to converge well enough into the core of the low. Moreover, wind shear could favour more or less mid-level dry air intrusion in the coming days. In this mixed context, latest guidance only suggests a marginal cyclogenesis potential until this weekend, and the few scenarios that develop a storm tend to do so in the Australian AoR. Models are still dispersed about the track of this low and the po
ssibility that it could enter or not Reunion's RSMC AoR, with only a low probability given by ensemble forecasts. Thus the risk is considered very low and post-poned to mid-week, given the current low's location.

The risk of development or entry of a moderate tropical storm on the eastern edge of the basin is very low from Wednesday.

South of Diego Garcia archipelago:
In the next few days, under the effect of a strengthening of north-westerly winds on the equatorial side of a rebuilding but short-lived Monsoon Trough west of 75E, a closed low could develop to the south-west of Diego Garcia. Although there is still some uncertainty about how efficient and long-lived surface convergence will be in place, some models suggest the possibility of cyclogenesis, with a low probability of tropical storm formation by the end of the week or this weekend. Large-scale equatorial wave
patterns could also help trigger convection in this area (active phase of the MJO moving over the Indian Ocean, adding to a transient Rossby wave, and also a Kelvin wave later on).

The risk of development of a moderate tropical storm to the south-west of Diego Garcia is low from Friday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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596
AWIO20 FMEE 241135

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/24 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The transequatorial flow has re-established West of 70E, while equatorial Westerlies are still present on the rest of the basin. Thus, a monsoon trough branch is currently developing near 10S. Convection is located on each side of the MT, within the slowing areas of the monsoon flow and trade winds respectively.

A wide clockwise circulation is present in the australian AoR since a few days. This weak low is monitored daily through BoM's IDW10800 Tropical Cyclone Outlook for the Western region.

In the Australian AoR :

The low-level cloud vortex remains well visible on the sat images with a center near 11.8S/91.6E at 09Z, convection being concentrated within the South-eastern quadrant. Max winds are estimated at 25 kt locally 30kt within the southern semi-circle. Currently quasi-stationary, the low should begin to track Westward shortly and could enter our basin by tomorrow afternoon. Within rather unconducive upper conditions (mid-level dry air, recurrent northwesterly upper shear) and with a clear lack of equatorward su
rface convergence, the system is not very likely to develop further.

The risk of development or entry of a moderate tropical storm on the eastern border of the basin is low from Wednesday.

South-west of the Chagos Archipelago :

Under the influence of the temporary monsoon burst, a closed circulation could emerge by Friday within the MT, south-west of the Chagos archipelago. Then, within neutral upper conditions and with a weakening low-level convergence, the potential for development of this low appears to be low for the next 5 days. This analysis is in good agreement with the ensemble prediction.

The risk of development of a moderate tropical storm to the south-west of the Chagos Islands is low from Friday.

At longer range : An active MJO phase is currently propagating over the Eastern half of the basin. A Kelvin wave is also expected to cross the basin from the African coasts to the East of the basin over next week. In response to this equatorial wave activity, only a low cyclogenesis signal is suggested by the Euro long-range forecasts.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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183
AWIO20 FMEE 251007

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/25 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) configuration centered between 8S and 10S east of 55E. Convective activity is moderate to strong on the equatorial side of this MT, but also in the area of slowing of the trade winds south of a large circulation centered approximately at 8S/65E.

At the eastern edge of the basin, in the Australian area of responsibility, the large clockwise circulation 21U continues to be monitored by the BoM, via the IDW10800 bulletins

In the Australian area:

Located around 11.6S/92.2E by the BoM at 06UTC, the circulation center, with maximum winds in the order of 25kt in the SW quadrant, could enter our area of responsibility starting tomorrow Friday. However, the environmental conditions do not really leave any potential for intensification of this circulation during the next few days.

The risk of development of a moderate tropical storm on the eastern border of the basin is low from Friday.

Southwest of the Chagos Archipelago:

The partial ASCAT swath of 0403UTC does not allow to precisely define a closed circulation southwest of the Chagos Islands, which could be located around 7.5S/63.8E at 0900UTC. It is necessary to wait for this circulation to consolidate during the next few days for the development potential to be a little more marked. Thus a risk of reaching the threshold of a moderate tropical storm begins to be noticeable in the guidances from 3/4 days

The risk of development of a moderate tropical storm to the south-west of the Chagos Islands is moderate from Monday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$
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808
AWIO20 FMEE 261242

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/26 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a monsoon trough (MT) configuration between 50 and 75E centered between 8S and 10S. Further east, a Near Equatorial Trough (NET) pattern persists with westerlies just south of the equator. The convective activity is moderate in the flows slowing down area but also near the two suspect areas located east of Agalega and in the Australian AoR.

In the Australian region:

Located near 10.7S/91.0E according to the BoM at 06UTC, the system is still weak given to the latest scatterometer data. The 0833Z SSMI swath shows that the convective activity is shallow near the center.

Despite a good upper level divergence, this minimum is restrained by a moderate westerly shear bringing dry air, and a lack of surface convergence. Indeed, over the next few days, the circulation should progressively lose its equatorial feeding due to the strengthening of the westerlies and their bending towards the northern hemisphere (Kelvin wave + MRG) but also due to the lack of surface convergence on the polar side north of a deep trough. This minimum should disappear in the next few days over the extr
eme east of our area of responsibility.

Development of a moderate tropical storm over the easternmost parts of our basin is not expected anymore.

East of Agalega:

Thanks to good feeding on the equatorial side (20/25kt monsoon flow) and to a lesser extent on the polar side, the suspect area between Agalega and Diego-Garcia is showing signs of development with increasing curvature in the cloud pattern. Nevertheless, according to partial ASCAT data and high resolution satellite images, it seems that the inner core of the circulation is still quite broad. A swirl of clouds rotating around a center drowned in the convective mass, can be seen around 9.4S/66.6E at 11Z.

This system does not benefit from particularly favorable conditions. Despite a good feeding on the equatorial side, the trade wind flow is weak on the far edge of the subtropical ridge. A weak to moderate easterly shear also seems to limit the potential for development at shorter range. On Sunday, while the trade wind flow is strengthening with the arrival of the new high-pressure cell to the south, the surface convergence on the northern side is weakening, with the westerly flow bending towards the norther
n hemisphere (Kelvin wave + MRG). Mid next week, on the edge of the NET, the system could find a more conducive environment for its deepening. But for now, the main guidance is now keen to significantly deepen that low, especially those of NOAA. IFS in its last run still suggest gale force winds on Sunday.

The risk of development of a moderate tropical storm, south-west of the Chagos Islands is moderate up to Monday, and then low from Tuesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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514
AWIO20 FMEE 271130

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/27 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 001/15/20202021 issued on Tropical Depression no15-20202021 at 06 UTC.

Next warnings issued at 12 UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin has progressively shifted to a Near Equatorial Trough (NET) pattern East of 55E, with westerly winds south of the equator. The convective activity is weak to moderate within the Tropical Depression no15 in the ESE of Agalega and is currently monitored by the CMRS, and is the subject of regular warnings today. Convective activity is also observed in the northern Mozambique Channel as well as along the East coast of Madagascar.

In the Australian's AoR:

A low-pressure area located around 10.2S 89.6E at 06UTC, is currently monitored by the BOM (bulletin IDW10800) , west-northwest of the Cocos Islands. The 0330Z ASCAT-C swath showedan elongated and ill-defined clockwise circulation, with mean winds at 20kt maximum in the weak convection zone in the South semi-cercle. This vortex is tracking very slowly towards the West and should, given to the latest available guidance, enter our area of responsibility early next week at a very weakened stage, given the poor
environmental conditions to come. In fact, the low level convergence will not be sufficiently organized for the flows to converge effectively within the structure. In addition, aloft, the system should also undergo this weekend a NE windshear promoting the intrusion of dry air in the mid troposphere.

Thus, according to these elements, there is no longer a risk of a moderate tropical storm forming over the extreme east of the basin.

Depression Tropicale 15-20202021:

Position a 09UTC: 10.3oS / 65.7oE
Max 10 mn wind: 30 kt
Motion: ESE a 3 kt
Estimated central pressure: 998 hPa

The risk of formation of a Moderate Tropical Storm southwest of the Chagos remains moderate until Monday.
For more information about this system, please refer to the bulletins that will be issued at 12UTC and followings.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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233
AWIO20 FMEE 281112

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/28 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no 001/15/20202021 issued on Tropical Depression no15-20202021 at 06 UTC.

Next warnings issued at 12 UTC

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a vague Near-Equatorial Trough (NET) pattern, centered around 11S.

Convective activity over the basin is dominated by two low pressure circulations embedded within this broad NET : Tropical Depression 15 which is monitored by the RSMC as well as a low that has recently come from the Australian AoR and is now on the extreme East of our basin.

An equatorial westerly wind surge is currently underway east of 60E, mainly driven by an active phase of the MJO crossing from central to eastern Indian Ocean.

Tropical Depression 15-20202021:

Position at 09UTC: 11.5oS / 68.5oE
Max 10mn winds: 30 kt
Motion: ENE, 6 kt
Estimated minimum pressure: 1000 hPa

Until mid-week, Tropical Depression 15 will encounter unfavourable conditions which will lead to its gradual weakening and eventually make it vanish within the NET.
For more informations, please refer to bulletins WTIO20 and WTIO30 issued at 06UTC and following.

On the extreme East of the basin, the low pressure area which was recently in the Australian AoR is now located by 10.3S / 88.1E as of 09UTC, with 15 to 20 kt max winds and an elongated circulation. In the coming days, moderate wind shear and a dry mid-troposphere combined with a lack of equatorward low-level convergence should seriously limit chances of development.

By the end of the week, poleward surface convergence due to strengthening trade winds should help increase vorticity within the NET. Some models suggest that this could initiate a possible cyclogenesis from Friday or Saturday close to 70E, potentially from one of the pre-existing vorticity areas mentionned above. This potential system could benefit from good upper divergence on the edge of a rebuilding mid-tropospheric ridge. Thus chances of a new cyclogenesis increase at the end of the forecast range.

The risk of development of a Moderate Tropical Storm to the South-West of the Chagos archipelago becomes very low from Friday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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956
AWIO20 FMEE 291132

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/29 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Near-Equatorial Trough (NET) pattern, centered around 10S. An equatorial westerly wind surge is currently underway east of 60E, mainly driven by an active phase of the MJO moving across the eastern Indian Ocean.

Convective activity over the basin is mainly organized around two weak low pressure areas embedded within the NET (remnants of former Tropical Depression 15 as well as a low on the extreme East of the basin) but also in some convergence areas to the north-west and south-east of Madagascar.

Former Tropical Depression 15-20202021 is now a remnant low and isn't monitored by the RSMC anymore since it will soon dissipate. It was located near 9.4S/70E at 0900Z with max winds estimated around 20 kt. The other low pressure area to the east of the basin was located at 0900Z around 9.5S/87E. Its max winds are estimated at 15kt in a broad and elongated circulation. Because of wind shear and dry air aloft as well as lack of equatorward surface convergence, both of these vorticity areas have no potential
for development in the short run and should more or less dissipate within the NET by mid-week.

Later on by this weekend, current guidance suggests improved poleward surface convergence due to strengthening trade winds on the northern edge of a subtropical high. However, equatorward convergence remains more uncertain, with still some dispersion among model scenarios, more or less favourable. Moreover, a rebuilding upper tropospheric ridge north of the Mascarene islands around 15S should improve upper level conditions (less shear, more upper divergence). Some models suggest that these conditions could
help initiate cyclogenesis from Friday or more likely Saturday close to 60/70E and 10/15S, which means north/north-east from the Mascarene islands. However, there still is some uncertainty about how much and well all these ingredients will fit together (low level convergence, sufficient atmospheric moisture or not...). Potential will need confirmation in the coming days.

The risk of development of a new Moderate Tropical Storm becomes low from Saturday to the far north-east of the Mascarene Islands.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
--- SBBSecho 3.12-Linux
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047
AWIO20 FMEE 301201

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/30 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:

The basin is in a Near Equatorial Trough (NET) pattern centered around 9S, East of 60E. A westerly surgewesterlies is underway over the northern part of the basin, driven by a good wave activity (active phase of the MJO and the Kelvin). The convective activity observed over the basin is mainly organized within the NET near the two low-pressure minimums (remnant low of the former tropical depression no15 as well as a vortex located on the extreme east of the basin). Convective activity is also observed betwe
en the east coast of Madagascar and Reunion Island, but also in the northern Mozambique Channel.

The former tropical depression 15-202021 (now a remnant low) was located at 09UTC around 9.4S/68E with a closed but elongated low layer circulation, with mean winds estimated at 15 kt according to the last scatterometer swaths. The central pressure is estimated at 1005 hPa. The second low was located in the extreme East of the area, was centered around 11.3S/82E at 09UTC with mean winds close to 15 kt according to the last partial ASCAT data, and presents a very stretched circulation from West to East. The
central pressure is estimated at 1003 hPa. According to the CIMMS data, these two vortex are currently undergoing rather unfavorable environmental conditions due to a sheared and rather dry context aloft and a low level convergence that struggles to converge within the TPE. Thus, until Friday, these weak lows do not have any real potential for development, and should gradually dissipate in the TPE.

This weekend, most deterministic models suggest an improvement in environmental conditions, but give a signal of cyclogenesis that remains weak. Indeed, from Saturday, the low level convergence slowly improves: the westerly flow strengthens and becomes more convergent, taking a more trans-equatorial flow, which also improves the basin pattern. The monsoon flow is also improving by converging more within the monsoon trough. Nevertheless, the deep layer wind shear is still present, which could slow down the
cyclogenesis potential. At this stage, there is still considerable uncertainty in the models, particularly in terms of timing. The IFS and GFS models develop a beginning of cyclogenesis from Saturday mainly in the northeast of the Mascarene archipelago. Thus, a new cyclogenesis is possible this weekend, but is still subject to a large amount of uncertainty. This potential remains to be confirmed during the next days.

The risk of development of a new Moderate Tropical Storm in the Northeast of the Mascarene archipelago remains low from Saturday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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184
AWIO20 FMEE 311051

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/03/31 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Near Equatorial Trough (NET) configuration oriented towards 8S, east of 60E, with a burst of equatorial westerlies. The moderate to strong convective activity is mainly concentrated within the NET near the two low-pressure minimums that are the remnant low of the tropical depression no15 and a vortex located on the extreme east of the basin. This area defines a large low-pressure circulation whose last ASCAT passes do not allow to define precisely a circulation center.

The convective activity should continue during the next few days but the environmental conditions (lack of equatorial inflow due to the equatorial west winds) are not conducive to the establishment of an effective closed circulation. Under these conditions, the risk of a moderate tropical storm in this area and over the rest of the basin becomes zero over the next 5 days. It is necessary to wait for longer periods for the equatorial winds to resume a component more conducive to low level convergence.

The convective activity is also present in the area of slowing of the southern flow that goes up the channel at the level of the coast of Tanzania.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
--- SBBSecho 3.12-Linux
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325
AWIO20 FMEE 011206

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/01 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Near Equatorial Trough (NET) configuration axed between 4S and 9S, east of 55oE. Convective activity is globally decreasing compared to yesterday. Convective activity exists mainly south of the NET around 10oS between 70oE and 80oE in the area of slowing of the trade winds and on the southern edge of a zone of preferential low levels vorticity around 70oE within the NET. Over the extreme west of the basin and off the coast of Tanzania, thunderstorm activity remains strong in the strong low
levels convergence and confluence between the southerly winds moving up towards the equator along the African coast and the south-easterly trade winds around the northern tip of Madagascar.

Over the next few days, a low could form in the first part of next week in the NET east of 65oE. However, these chances of a tropical storm evolution by Tuesday are not significant for the moment with an indirect low-level convergence and an increasingly dry air mass on the equator side with the arrival of the dry phase of the MJO by the west of the basin.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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358
AWIO20 FMEE 030716

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/03 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


A near-equatorial trough (NET) is now well established with its axis along 5S on the Western half of the basin and 6-8S on the East.

Convection is mainly located on the Eastern half of the NET, East of 85E. Although weaker, convection is also located on the Chagos region, on the Comoros region and along the African coasts.

Over the week-end, a westerly burst along the equator associated with the MJO wave, and an arriving mixed Rossby-Gravity wave should improved the eaquatorial convergnce, and then trigger the emergence of a clockwise closed circulation within the NET East of the Chagos. Then from Monday, in spite of a nice upper divergence, low-level conditions become more neutral again with the decrease of the surface equatorial convergence, but remaining polarward. Thus, the available guidance suggest a slow development
of the weak system. The ensemble forecast is in good agreement with this scenario and suggest a cyclogenesis risk from Wednesday, potentially moderate over the second half of the week.

The risk of development of a moderate tropical storm becomes low from Wednesday East of the Chagos.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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844
AWIO20 FMEE 041128

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/04 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


A near-equatorial trough (NET) is established east of 60E, along a tilted axis going from 5S to 9S west to east.

Convection is mainly located on the eastern half of the NET, east of the Chagos, and extends towards the Australian Area of Responsibility where even more intense convection is currently favored by an ongoing active MJO phase. On the western side of the basin, convection is generally weaker due to the dry phase of the MJO moving in from Africa, with small pockets of convection found around the Comoros, the African coast and to the south-east of Madagascar.

Until tomorrow, MRG and ER waves will trigger better poleward convergence on the northern edge of the NET, which could form a closed circulation by Monday evening or Tuesday close to 8-9S and 80-85E. The rapidity of this process and the longitude of the newly formed low still remain uncertain. The low level steering flow will also make it track eastward quite rapidly and eventually cross into the Australian AoR between Wednesday and Thursday according to latest guidance. Moreover, environmental conditions s
hould then become less favorable for development and the presence of other more-developped tropical systems in the AoR seems to badly interfer with low level convergence in the eastern semi-circle of the system. Thus there is only a narrow time and space interval in which this system could develop, and only a few model runs have it intensify sufficiently fast and west to make it reach tropical storm strength west of 90E. The prevailing option calls for max winds staying at
or below
near-gale strength.

The risk of development of a Moderate Tropical Storm becomes very low from Wednesday on the eastern edge of the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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142
AWIO20 FMEE 051220

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/05 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


A near-equatorial trough (NET) is established east of 60E, along a tilted axis going from 5S to 10S from west to east.

Convection is mainly located on the northern side of the NET. On the western side of the basin, convection is generally weaker due to the dry phase of the MJO moving in from Africa.

On the eastern side of the basin :

The latest scatterometric and microwave data do not show, for the moment, the presence of closed circulation within the NET. The satellite images show a area of stronger vorticity towards 84E. This area benefits from a good surface convergence, especially on the northern side, and from an excellent upper divergence, but suffer meanwhile from a moderate easterly shear (around 15kt according to the CIMSS data)

During the next few days, this circulation could develop thanks to a temporary decrease in the shear. However, it should quickly reach the Australian area simultaneously, probably by Wednesday morning. This system therefore has a very short window to develop into a tropical storm in our AoR. Few members of the EPS succeed in suggesting such a scenario therefore giving a global very low risk. This likelihood is maintained even if it may be a bit too cautious.

The risk of development of a Moderate Tropical Storm is very low up to Wednesday on the eastern edge of the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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492
AWIO20 FMEE 061101

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/06 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a near-equatorial trough (NET) configuration with an inclined axis of 5S to 10S from west to east, east of 60E. Convective activity remains mainly localized on the equatorial side of this NET and at the eastern end of the basin at the level of the circulation followed for several days through this bulletin. The activity is also moderate to strong in an axis of convergence of flows between Madagascar and Reunion and more modestly along the Tanzanian coast.

East of the basin:

The latest ASCAT swath data do not allow to estimate winds associated with the closed circulation located at the eastern end of the basin around 88E/10S. The HY-2B and 2C data from the previous day allow to estimate an elongated circulation reaching values of 25/30kt under convection. During the next 24-48h, this circulation could develop modestly thanks to a temporary decrease of the shear but it should nevertheless reach the Australian area of responsibility zone by Wednesday.

The risk of formation of a Moderate Tropical Storm over our basin has become null due to the passage of the suspect circulation in the Australian area of responsibility.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
--- SBBSecho 3.12-Linux
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952
AWIO20 FMEE 081118

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/08 AT 1200 UTC

PART 1:

WARNING SUMMARY:

Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:

The basin is in a near-equatorial trough (NET) pattern oriented along 09oS east of 70oE. Further west, a low-level trough, with some characteristics of a poorly defined Monsoon Trough, exists along 5oS between 50oE and 65oE.

The associated convective activity is globally weak while a dry phase of the MJO is taking place in the basin. In this context, a drier than normal weather is expected during the next two weeks in the near equatorial zone of the Indian Ocean (ie mainly north of 10oS and east of 55oE), accompanied by a NET pattern less and less defined. Only the northern part of the Mozambique channel and the northeastern sector of Madagascar, located in an area of enhanced low levels convergence within the trade wind, shoul
d keep a weather more humid than normal. The risk of a new cyclogenesis is therefore negligible during the next 5 days and even appears very unlikely by the end of April.

There is no risk of a Moderate Tropical Storm forming over our basin in the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
--- SBBSecho 3.12-Linux
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042
AWIO20 FMEE 101249

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/10 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a near-equatorial trough (NET) pattern east of 60E and along 5S to 8S from west to east.

Within an ongoing dry phase of the Madden-Julian oscillation (MJO), convection along the ITCZ is generally weak. Nevertheless, a broad and elongated clockwise circulation associated with moderate convective activity can be found to the east of the Chagos archipelago, embedded in the NET. Moreover, sparse active storms are still ongoing close to the Comoros and off eastern Madagascar's coast.

In a large-scale unfavorable background (dry MJO phase, moderate wind shear), the circulation embedded in the NET and centered around 79E/7S this Saturday is the only area that has a small potential of development by the end of next week, according to some determinist NWP models. Some slightly more favorable conditions could emerge, especially the strengthening of eastnortheast winds on the equator side of the NET helped by a weak Equatorial-Rossby wave, which could improve low level convergence with the
trade winds. Improved upper divergence under the upper-tropospheric ridge could also be a factor, and a moderatly moist mid-troposphere in that area could resist the MJO-triggered "dry invader" (still a bit uncertain though). Thus a few model runs have it develop into a weak tropical storm at the end of next week. Scenarios remain dispersed and the unfavorable large-scale conditions are reflected by a still very shy ensemblist signal. Consequently, the risk is still very low
and will need further confirmation in the coming days.

Risk of development of a Moderate Tropical Storm is very low from next Thursday near the Chagos archipelago.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
--- SBBSecho 3.12-Linux
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820
AWIO20 FMEE 110959

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/11 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a Near Equatorial Trough (NET) configuration east of 62E along an axis from 4S to 7S from west to east, ending east of the low-pressure circulation area located around 81E/7S. The ASCAT swath of 0425UTC allows to estimate winds of 20kt in the northern semicircle. Associated with this circulation, the convective activity is moderate to strong and should persist for 2 to 3 days. However, in the context of a dry phase of the MJO over the basin and being in a moderately sheared environment, this
area does not have the potential for significant intensification over the next few days.

Over the next 5 days, there is no risk of a moderate tropical storm forming over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
--- SBBSecho 3.12-Linux
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781
AWIO20 FMEE 131228

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/13 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a poorly defined Near Equatorial Trench (NET) configuration between 55oE-80oE and 06oS-10oS. The associated convective activity is decreasing compared to yesterday. It is present near two zones of preferential vorticity of low layers present within this NET. The first one has been present for a few days at the eastern end of this TPE and is located today approximately at 8.5oS and 80oE. The second one appeared during the last 24 hours more to the West towards 7oS and 70oE. In a context
of dry MJO well marked on this near equatorial zone of the central Indian Ocean, the environmental conditions remain unfavorable to cyclogenesis in particular at the level of the convergence of low layers and the moisture content of the atmosphere.

Elsewhere in the basin, convective activity is strong over a large northern part of the Mozambique Channel (including the Tanzanian and northern Mozambican coasts, the Comoros archipelago and the north-western region of Madagascar) as well as between the north-eastern coasts of Madagascar and the Mascarene Islands. These regions are subject to persistent rainy-stormy developments that will continue during the next few days, without however forming some suspicious area.

During the next 5 days, there is no risk of formation of a moderate tropical storm over the basin.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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480
AWIO20 FMEE 141242

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/14 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin remains in a poorly organized Near-Equatorial Trough (NET) pattern between 50oE-80oE and 05oS-10oS.

Compared to yesterday, convection associated with the NET has been concentrating more distinctly around two vorticity areas, and especially the clockwise circulation that has already been mentionned these last days and which is now getting more defined near 9oS and 81oE, on the eastern edge of the NET. Latest satellite images show improved convergent thunderstorm bands and some upper-level divergence, which are signs of an improving structure. Latest ASCAT data still shows a rather elongated circulation, wi
th winds around 20 kt.

The dry MJO phase is still established over the central Indian Ocean near the equator and thus still lowers the large-scale odds of storm development, mainly through unsufficient equatorward low level convergence and lack of atmospheric moisture. However, today's latest NWP output has displayed slightly increased chances of development of the aforementioned circulation. This Wednesday's 00Z and 06Z GFS runs have even simulated a compact midget-like tropical cyclone for this weekend. Such an excessive option
is considered unrealistic but hints about slightly improving environmental conditions. Some of today's EPS members suggest potential storm formation, which wasn't the case yesterday, as well as some other deterministic models do. According to current guidance, this system should start tracking westward from Thursday, moving into a more favorably low-sheared environment (no more than 10 to 15 kt) and under modest upper divergence. In these conditions, the possibility of a s
mall-siz
ed system developping into a tropical storm by this weekend can't be completely ruled out, even though large-scale lack of moisture and low level convergence seriously play against it. Should it develop into a storm, no inhabited lands will be on its path until next Monday although it could get close to the Agalega archipelago at the extreme end of the forecast period.

During the next 5 days, the risk of development of a moderate tropical storm over the basin is considered very low from Saturday and low from Sunday
nwards.

Elsewhere in the basin, convective activity is strong over a large northern part of the Mozambique Channel (including the Tanzanian and northern Mozambican coasts, the Comoros archipelago and the north-western region of Madagascar) as well as between the north-eastern coasts of Madagascar and the Mascarene Islands. These regions are subject to persistent rainy/stormy developments that will continue during the next few days, without however forming any suspicious areas.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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227
AWIO20 FMEE 161202

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/16 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The convective activity is weak over the basin within this dry MJO phase with weak winds all along the equator without particular pattern. A suspect area is nevertheless present south of Diego Garcia probably favored by an equatorial Rossby wave.

A weak clockwise circulation is visible today south of Diego-Garcia around 10S/74E at 11Z. The last analyses gives an estimate of the maximum winds around 15/20kt far from the center in the southern semicircle.

This vortex will encounter unfavorable environmental conditions for its development over the next few days as it moves westward. Indeed, given the current basin pattern and the unfavorable wave activity (dry phase of the MJO), the convergence on the equatorial side will remain inexistent, in spite of a sufficient trade wind flow on the polar side. By the beginning and middle of next week, thanks to a small strengthening of the upper level divergence, some deterministic models suggest a more or less pronounc
ed deepening of the system north of Madagascar. Only a few members of the European model ensemble forecast propose the formation of a storm. There is no threat to the inhabited territories during the next 5 days.

During the next 5 days, the risk of development of a moderate tropical storm over the basin is very low from Tuesday.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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232
AWIO20 FMEE 171023

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/17 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


Convection is rather weak over the basin under the influence of a dry MJO phase. With no wind at the equator, no large-scale configuration is
stablished.

However, an equatorial Rossby wave allow for the survival of a weak and ill-defined clockwise circulation in the South-West of the Chagos archipelago with 20-kt max winds within the southern semi-circle. Convection remains ill-organised around this weak system.

As the system drifts westwards over the next days, mid and upper conditions become more conducive for its development with increasing mid-level moisture and upper divergence. On the other hand, equatorward low-level convergence remains nonexistent. The last ensemble and deterministic model runs suggest an increase of the cyclogenesis risk compared to previous simulations. The strengthening of the trade winds suggested by the models may be sufficient to constitute a better defined surface circulation and lau

nch a slow cyclogenesis process.

The risk of development of a moderate tropical storm developing North of Madagascar becomes low Wednesday.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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772
AWIO20 FMEE 181037

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/18 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


Convection is rather weak over the basin under the influence of a dry MJO phase. With no wind at the equator, no large-scale configuration is
stablished.

However, an equatorial Rossby wave allow for the survival of a weak and ill-defined clockwise circulation in the South-West of the Chagos archipelago. The latest Ascat-B data from 05h30utc, show maximum winds of about 20kt in the southern semicircle and western quadrant, around a center located around 10.5S/65E. Convection remains ill-organised around this weak system.

As the system drifts westwards over the next days, mid and upper conditions become more conducive for its development with increasing mid-level moisture and an increasing altitude divergence on the polar side as the axis of the jet rises towards the North.. On the other hand, equatorward low-level convergence remains nonexistent. The last ensemble and deterministic model runs suggest an increase of the cyclogenesis risk compared to previous simulations from Wednesday,. The strengthening of the trade winds
suggested by the models may be sufficient to constitute a better defined surface circulation and launch a slow cyclogenesis process.

The risk of development of a moderate tropical storm developing becomes low Wednesday, North of Madagascar, then to the north of the Comoros archipelago.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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452
AWIO20 FMEE 191016

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/19 AT 1200 UTC

PART 1:

WARNING SUMMARY:

Warnings WTIO20 and WTIO30 no001/16/20202021 on the zone of disturbed weather no16-20202021 to be issued at 12UTC.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is in a trade wind configuration east of 70E and has a large area of low pressure west of 70E. The convective activity remains globally weak to moderate over the basin. It is particularly concentrated west of 70E, north of the Mozambique Channel along the coast of Tanzania and on the southern side of the large low-pressure area, around 12S/57E.

Within this zone, the last ASCAT swath of 0348UTC does not allow to locate clearly a closed circulation but notes winds of about 25kt (locally 30kt under convection) in the South sector by gradient effect, defining the zone of disturbed weather 16-202021 for which the first monitoring bulletins will be issued at 12UTC. A small closed circulation can be suspected around
0.7S/57.8E.

Zone of disturbed weather 16-20202021:
Position at 09UTC: 10.7S/57.8E
Max 10min wind : 25kt
Motion : West at 13kt
Estimated central pressure : 1007 hPa

Excluding this system, during the next few days, there is a risk of formation of a baroclinic system south of the Mozambique Channel but without possible evolution to a tropical system.

Therefore, during the next 5 days, there is no risk of another moderate tropical storm forming over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
h

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732
AWIO20 FMEE 201145

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/20 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no002/16/20202021 on the Tropical Depression no16-20202021 issued at 06UTC. Next to be issued at 12Z.

PART 2 :
TROPICAL WEATHER DISCUSSION:


SWIO basin flow is mainly driven by a moderate trade wind flow hardly reaching the equator without encountering any transequatorial/westerly flow. Convective activity is mainly located around Tropical Depression 16-20202021.

Tropical Depression 16-20202021:
Position at 09UTC: 10.9S/51.7E
Max 10min wind : 30kt and 35kt locally in the south-western quadrant.
Motion : West at 12kt
Estimated central pressure : 1002 hPa

During the next 5 days, there is no risk for an other moderate tropical storm to develop over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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287
AWIO20 FMEE 211106

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/21 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no006/16/20202021 on the Severe Tropical Strom JOBO issued at 06UTC.

Next to be issued at 12Z.



PART 2 :
TROPICAL WEATHER DISCUSSION:


SWIO basin flow is mainly driven by a moderate trade wind flow hardly reaching the equator without encountering any transequatorial/westerly flow. Convective activity is mainly located around Severe Tropical Storm JOBO.

Severe Tropical Storm JOBO:
Position at 10UTC: 9.7S/47.9E
Max 10min wind : 60kt
Motion : WNW at 5kt
Estimated central pressure : 989 hPa

During the next 5 days, there is no risk for an other moderate tropical storm to develop over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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417
AWIO20 FMEE 221041

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/22 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO20 and WTIO30 no010/16/20202021 on the Severe Tropical Strom JOBO issued at 06UTC.

Next to be issued at 12Z.



PART 2 :
TROPICAL WEATHER DISCUSSION:


SWIO basin flow is mainly driven by a moderate trade wind flow hardly reaching the equator without encountering any transequatorial/westerly flow. Convective activity is mainly located around Severe Tropical Storm JOBO.

Severe Tropical Storm JOBO:

Position at 10UTC: 9.38S/45.17E
Max 10min wind : 50kt
Motion : WNW at 8kt
Estimated central pressure : 990 hPa

During the next 5 days, there is no risk for an other moderate tropical storm to develop over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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171
AWIO20 FMEE 230946

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/23 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO22 and WTIO30 no014/16/20202021 on the Moderate Tropical Storm JOBO issued at 06UTC.

Next to be issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The trade wind is dominant over the southwest Indian Ocean basin west of 70E, reaching the equator with difficulty. Further east, an area of low pressure allows the establishment of a trans-equatorial flow not very marked. The convective activity is focused at the level of the moderate tropical storm JOBO in the North of the Mozambique Channel and more modestly on the southern side of the low pressure area in the East of the basin.

South of the Mozambique Channel, the convection is also moderate in connection with the beginning of a baroclinic deepening that should not persist.

Moderate Tropical Storm JOBO:
Position at 09UTC: 8.8S/43.9E
Max 10min wind : 40kt
Motion : WNW at 4kt
Estimated central pressure : 999 hPa

During the next 5 days, there is no risk for an other moderate tropical storm to develop over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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920
AWIO20 FMEE 241138

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/24 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Warnings WTIO22 and WTIO30 no18/16/20202021 on Filling Low JOBO issued at
6UTC.

Next and last warnings to be issued at 12UTC.



PART 2 :
TROPICAL WEATHER DISCUSSION:


The trade winds flow prevails across most of the southwest Indian Ocean basin. East of 70oE, weak equatorial westerlies define a frail near-equatorial trough (NET) over the northeastern part of the basin, centered around 3 to 4oS.

Convective activity is mainly focused near the filling low JOBO along the coasts of Tanzania and extreme north-east Mozambique. It is weaker on the southern edge of the NET and elsewhere.

Moreover, south of the Mozambique Channel and east of the South African coast, an emerging subtropical-like low analyzed around 29oS/33oE has winds close to 25 to 30 kt, locally reaching 35 kt in the vicinity of thunderstorms.

Available guidance doesn't suggest any development of a tropical or subtropical storm from these different areas of vorticity over the coming days.

Filling Low JOBO :
Position at 10UTC: 7.2S/40.0E
Max 10min wind : 25/30 kt
Motion : WNW at 10 kt
Estimated central pressure : 1005 hPa

During the next 5 days, there is no risk for an other moderate tropical storm to develop over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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642
AWIO20 FMEE 250954

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/25 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The trade wind flow is dominant over southwest Indian Ocean basin with a weak near equatorial trough (NET), east of 70oE over the northeast part of the basin, centered at 4oS. The most pronounced convective activity is concentrated in several places over the basin:

- on the polar side of the NET at the location of a weak clockwise circulation around 5S/78E

- along the Mozambican and Tanzanian coasts in the wake of the overland depression JOBO

- north of Madagascar around 7S/50E

On the other hand, south of the Mozambique Channel and east of the South African coast, a low-pressure system is in progress towards 27.7S/34.6E, with winds analyzed around 25 kt.

The available models do not suggest any intensification into a tropical or subtropical storm of these areas of vorticity in the coming days.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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832
AWIO20 FMEE 261057

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/26 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


First signs of a winter configuration, the trade wind flow is dominant over the southwest Indian Ocean basin.

The convective activity is weak to moderate and is mainly concentrated on the polar side of a weak low-pressure circulation around 5S/76E, along the eastern coast of Madagascar and at the level of a convergence of flow south of the Mozambique Channel associated with a baroclinic deepening can be marked around 30S/39E at 09UTC.

Related to this last area, the ASCAT swath of 0449UTC allows to estimate winds of about 35kt (locally 40kt under convection) in the North-East sector of this circulation. The CIMSS data allows us to estimate that the wind shear conditions are totally unfavorable to an intensification. However, the upper air dynamics can temporarily boost the convection. The maintenance of convective activity will not be long enough to allow the establishment of a perennial subtropical low over this area.

The available models do not suggest any intensification into a subtropical storm in this area of vorticity.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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242
AWIO20 FMEE 271021

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/27 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


First signs of a winter configuration, the trade wind flow is dominant over the southwest Indian Ocean basin.

The convective activity is weak to moderate and is mainly concentrated in a zone of undulation of the trade wind between 4S and 16S from 68E to 76S, also along the east coast of Madagascar, and north of the Mascarene Islands

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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592
AWIO20 FMEE 281049

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/28 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The South-West Indian Ocean basin displays a winter-like configuration, marked by a prevailing trade wind flow. The convective activity is weak to moderate and is mainly concentrated in an area of undulation of the trade winds along an axis 24.3S-53.4E / 00.0-53.4E. It is also present to a lesser measure north of the islands of Aldabra and Astove (Seychelles archipelago).

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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734
AWIO20 FMEE 291133

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/29 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The South-West Indian Ocean basin is gradually transitioning towards a more winter-like pattern, marked by a dominant trade wind flow. Convective activity is weak to moderate and is mainly concentrated in various low level convergence areas located in the slowing of the trade winds (extreme North-East of the basin, off the Tanzanian coast, North-East of the Mascarene Islands).

Despite a large-scale equatorial wave context becoming more conducive over a large western half of the basin (approaching wet phase of the MJO from Africa, and a Kelvin wave crossing a Rossby-gravity wave), none of these convective areas has a potential for development until the beginning of next week due to lack of convergence on the equatorial side or because of too much vertical shear.

Nevertheless, a strong baroclinic interaction is forecast on Sunday off the south of Madagascar. The associated upper trough should evolve into a cut-off early next week and the surface low should progressively find itself in a more or less barotropic environment from Monday onwards, under the upper-level cyclonic cold core and detaching itself from the jet stream while hovering over mild surface waters (SSTs around 24-25oC), at a latitude probably located between 25oS and 32oS. These conditions are typical
ly conducive for a tropical transition, which some models suggest between Monday and Tuesday, with the formation of a symmetrical warm core by latent heat release associated with convection. In particular, the latest runs of the GFS model explicitly develop a subtropical storm from Monday evening. Nevertheless, there are still uncertainties related to the ability of the surface low to free itself sufficiently from its initial baroclinic context and to the ability of the ass
ociated
convection to generate a sufficiently deep warm core. This is reflected in the dispersion between models, which is still quite high. This risk will therefore have to be clarified in the coming days.

The risk of formation of a subtropical storm becomes low from Monday off southern Madagascar.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
--- SBBSecho 3.12-Linux
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612
AWIO20 FMEE 301222

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/04/30 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:

Ahead of an active phase of the MJO, low-level easterly wind anomalies predominate in the near equatorial zone, causing the trade wind to rise to latitudes very close to the equator without any particular low-level configuration. Locally, there is quite strong convection in the area of slowing of the trade winds or near eastern Agalega where an upper levels trough interacts with the low levels warm and humid air. We do not anticipate the appearance of a suspicious area during the next 5 days in the near equ
atorial zone.

On the other hand, it is in the subtropical zone that the situation deserves a particular monitoring for the next week: a strong baroclinic interaction is still forecast by all the models on Sunday south of Madagascar. The associated upper trough will isolate in a cut-off at the beginning of next week and a surface low, resulting from an undulation of a cold front, should progressively find itself in a more or less barotropic environment from Monday. This low should evolve within the upper levels trough, in
an area of weak vertical shear with surface waters at 24-25oC. These conditions are typically conducive to a tropical transition, which some models suggest between Monday and Wednesday, with the formation of a symmetrical warm core by latent heat release associated with convection. However, it is difficult to assess whether the window of favorable conditions will be sufficiently persistent for this complex process of tropical transition to take place until the end. Compare
d to yes
terday, the deterministic and ensemblistic guidelines suggest a slightly higher signal.

Initially, strong winds (near gale to gale force) will develop in the southern semicircle of the system from Sunday (until quite far from the center between 30S and 35S). The structure of the wind field could become more compact and symmetrical depending on the progress of the tropical transition in the following days.

The risk of formation of a storm of subtropical nature in the South of Madagascar becomes weak Sunday then moderate from Monday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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816
AWIO20 FMEE 011025

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/01 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin has a trade wind configuration over its entire width. Convective activity is moderate to strong in the area of slowing of the trade flow approaching the equator at 4S east of 60E. No suspicious area is detectable in the tropical zone.

On the other hand, it is in the subtropical zone south of the Mozambique Channel that the situation deserves monitoring. Currently, a baroclinic low is being formed around 29S/40E. Until Monday, the upper dynamics will define a low-level circulation in an environment that will become increasingly barotropic in a context of weakening vertical wind shear. These conditions are typically conducive to a tropical transition, which some models suggest between Monday and Wednesday. Winds reaching the 35kt threshold
are expected to be limited mainly to the southern part of the circulation but may justify RSMC monitoring of this clockwise circulation over a fairly short time frame due to the intrusion of air over this area on Tuesday/Wednesday followed by increasing wind shear.

The risk of formation of a storm of subtropical nature in the South of Madagascar is moderate from Monday.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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640
AWIO20 FMEE 021204

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/02 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The trade wind flows up 0S/5S over the whole basin where it converged but without the presence of an equatorial westerly flow. Eastern anomalies are indeed present at the level of the equator due to the arrival of a new active phase of the MJO. Convective activity is strong in the areas of slowing trade winds, especially towards Diego-Garcia, favored by a significant wave activity (Kelvin, Equatorial Rossby, MJO,...). Weak circulations are also present in this area around 2S/59E and 5S/66E. But they do not
have significant cyclogenesis potential lacking of equatorial/transequatorial flows.

On the other hand, south of the Madagascar, a subtropical phenomenon could occur. Currently, a baroclinic deepening is beginning around 27S/49E. Until tomorrow Monday, the upper dynamics will favor the deepening of this low pressure circulation. During the night of Monday to Tuesday, this minimum should encounter more favorable conditions for a tropical transition with its shift under the upper trough, causing a decrease in shear. These favorable conditions could last until Tuesday morning before a strengt
hening of the west-northwesterly shear ahead of a jet. However, the convective activity within this minimum may be insufficient to generate a deep warm core and allow a complete transition according to the latest forecast runs. This could be due to the presence of dry air within the circulation and/or an insufficient thermal instability with only -14oC at 500hPa for 23/24oC in SST. The latest models (apart from UKMO) are struggling to propose gale force winds beyond the beg
inning o
f the tropical transition (Monday to Tuesday night).

The risk of formation of a storm of subtropical nature, south of Madagascar is low to moderate from Monday evening to Tuesday evening.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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133
AWIO20 FMEE 031143

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/03 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin depicts a trade wind pattern over the entire width of the basin, up to 4S. The westerly flow is missing, however the trade wind flow converges to a lesser extent with a weak northwesterly flow north of the Seychelles archipelago, favored by an interesting wave activity (Rosby equatorial and low frequency) where a weak area of vorticity is observed near 4.7S / 56.9E but with a poorly defined LLC and without potential for cyclogenesis for the next few days given the lack of equatorial feeding. The c
onvective activity is also noticed in the slowing of the trade wind flow, over the extreme east of the basin, north and east of the Agalega archipelago, as well as in the mesoscale convergences between the Mascarene Islands and Madagascar, as well as on the Tanzania and Kenya coasts.

In the south of Madagascar, a subtropical phenomenon could be initiated. Currently, the deepening of a baroclinic low is in progress near 29.2S/46E by baroclinic interaction. Until Tuesday morning, the upper dynamics will contribute to the deepening of this low, which will gradually find itself in a barotropic environment, with the formation of a kind of a small temporary warm heart in the low layer. Quite quickly during the day on Tuesday, this low will pass on the western edge of the upper trough and will
be subject to a strong south-westerly wind shear, which, not only in the lack of sustained convective activity, will help to hinder the chances of forming a warm heart aloft. The low will quickly regain classic extra-tropical characteristics, evacuating towards the mid-latitudes, which seems to be suggested both by the latest guidance and by the latest phase diagrams.

So, the risk of formation of a storm of subtropical nature, south of Madagascar remains temporarily moderate until tuesday morning then low beyond.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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274
AWIO20 FMEE 041104

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/04 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


At the equator, the monsoon flow towards the northern hemisphere begins to dominate the general circulation, especially on the Eastern part of the basin. Convection is mainly triggering within the slowing area of the trade winds near 5S on the Western half of the basin.

South of Madagascar, an initiation of subtropical low is now clearly visible on sat imagery, materialized by a quasi-stationary low-level cloud vortex centered on 29.8S/44.3E at 09Z. Associated convection is rather scattered and mainly located on the South-Eastern quadrant, with moderately cold cloud tops.

This morning 0530Z and 0645Z ASCAT swath showed max winds reaching near gale force 30kt between 30nm to 80nm from the center over the Eastern semi-circle and up to 125 nm on the North-Eastern quadrant. The estimated central pressure is 998hPa. The available phase diagrams suggest a symmetrical but still shallow warm core, which is in good agreement with the observed evolution on the sat images of the last 12 hrs. Dry air remains nested over the center of the circulation and prevents the triggering of the co
nvection (thus hindering the constitution of the warm-core).

From tonight, the upper cut-off low which shielded the circulation from the shear until now is expected to drift South-Eastwards. This shift should leave the system unprotected and a strong West-South-Westerly shear will quickly make the organisation of a mid-level warm-core very unlikely. The clockwise circulation is expected to move East-South-Eastwards over the next days, before merging with a baroclinic cold front by Friday evening.

The risk of formation of a subtropical storm South of Madagascar is thus deemed low tonight and tomorrow, before disappearing from tomorrow evening.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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246
AWIO20 FMEE 051049

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/05 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


At the equator, the monsoon flow towards the Northern Hemisphere is temporarily present but still weak.

Convection is concentrated in the slowing down of the trade wind towards 9S.

Southeast of Madagascar, the remnants of the subtropical low are clearly visible on satellite imagery, materialized by a vortex of low-level clouds centred on 32S/49.5E at 09Z. The associated convection has almost disappeared over the center, and resists vertical wind shear only in lines of convergence far from the center in the eastern quadrant, marking the end of the development potential.

The ASCAT runs of 0515Z and 0630Z show that the max winds reach the near gale force 30kt far from the center from 50mn to 150mn from the center in the North quadrant.

The low pressure circulation is expected to shift east-southeast over the next few days before merging with a baroclinic cold front by Friday evening.

There is no risk of formation of a moderate tropical storm over the basin for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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164
AWIO20 FMEE 071058

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/07 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


No significant wind over the eastern part of the basin near the equator, while an equatorial westerly flow gradually strengthens over the western half, in the wake of the active MJO phase. Deep convection is mainly located off the African shores, within the slowing area of the Southerly winds coming from the Mozambique Channel.

No risk of development of a moderate tropical storm over the next 5 days.

In the longer term, tropical wave activity becomes more conducive for cyclogenesis with a Klevin wave crossing path with an Equatorial Rossby over the western half of the basin, as well as well-established equatorial westerlies thanks to the MJO. Thus, while the Euro ensemble and deterministic models do not suggest any TC formation, the American models forecast a significant cyclogenesis risk for the second half of next week.

The development of a moderate tropical storm is not expected over the basin for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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340
AWIO20 FMEE 091217

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/09 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


A near-equatorial trough pattern centered around 4S is in place west of 70E in connection with an equatorial westerly wind burst over the western basin driven by the ongoing active phase of the MJO. East of 70E, the trade wind flow manages to cross the equator from south to north. Due to this strong circulation anomaly, most of the basin's convective activity is concentrated a little south of the equator, between the African coast, the Seychelles and a little further east towards 65 or 70E, where the trade
winds converge with the axis of equatorial westerlies. In particular, on the right exit of the westerly wind surge, a low level clockwise circulation has appeared this Sunday in the vicinity of 4.3S/62.4E, confirmed by this morning's ASCAT passes, which indicate winds of 20 to 25kt in its northwestern semi-circle, and associated with strong convection.

In the next few days, the equatorial westerlies linked to the MJO will also be reinforced by the passage of a Kelvin wave, which will also be superimposed with an Equatorial-Rossby wave, all of which should boost vorticity and convection on both sides of the equator, especially in the vicinity of the aforementioned clockwise circulation.

NWP models differ on the response to this strong wave activity and on the cyclogenesis potential of this low-pressure circulation : while American models (GFS, GEFS) remain very reactive by the end of the week, suggesting a potential tropical storm near the Seychelles, most of other models, including the European model and its EPS, maintain a circulation that is too elongated and weak, but on the contrary favor development north of the equator, in a more or less symmetrical location compared with the low we
are interested in. As the American model's option is too isolated, its scenario has been discarded for the time being and the risk of cyclogenesis in our basin is therefore considered to be close to zero until Friday. Nevertheless, it will be worth keeping an eye on it for the following days.

Development of a tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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559
AWIO20 FMEE 110957

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/11 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


Convective activity remains strong near the equator over the western half of the basin, under the influence of an active MJO phase. A Kelvin wave has also developed over this area and is expected to propagate Eastward over the next days, strengthening the equatorial westerlies.

Within this large-scale context, a near-equatorial trough is still located between 50E and 70E but the strong northwesterly upper shear and the lack of equatorward low-level convergence strongly impedes the development of a tropical low.

By the end of the week, an Equatorial-Rossby wave train is expected to cross the path of the MJO/Kelvin waves. Some models thus suggest a cyclogenesis risk. This signal is mainly suggested by the American ensemble and deterministic models but note that the last euro ensemble prediction suggest a slight increase in its cyclogenesis probabilities early next week.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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244
AWIO20 FMEE 121114

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/12 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The South-West Indian Ocean basin has a trade wind configuration that pushes the near equatorial trough axis very close to the equator towards 2oS. The convective activity remains strong near the equator and more fragmented in the area of slowing of the trade winds towards 10oS. The large-scale wave context remains unchanged (active phase of the MJO and Kelvin wave), which favors the maintenance of this convective activity near the equator.

In the presence of an upper wind shear over this area of convective activity, we can estimate that there is no risk of a significant low-pressure circulation being set up over the next 5 days.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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682
AWIO20 FMEE 131144

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/13 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The South-West Indian Ocean basin displays a near equatorial trough pattern with an equatorial westerly flow shifted into the northern hemisphere. Convective activity is strong in the northern hemisphere near a probable upcoming cyclogenesis. In the southern hemisphere, activity is present near Gan and Diego-Garcia, especially in the slowing down area of the trade wind flow towards 76E near the equator. This configuration is largely due to the significant wave activity (MJO, Kelvin and Equatorial Rossby).

Over the next few days, a closed low-level circulation could form in this area, driven by good surface convergence, especially on the polar side, and good upper divergence on the western side. However, the potential for cyclogenesis thereafter could be limited by several factors. The circulation could indeed be exposed to a moderate north-easterly shear. Moreover, its initial position close to the equator and the weakness of the trans-equatorial flow limited by the cyclogenesis north of the equator could li
mit its development.

In this context, numerical models are beginning to converge towards a common scenario.They propose the formation of a closed low-level circulation in the next few days and its migration southwards. Nevertheless, they still differ on the rapidity of development. Nevertheless, they still differ on the rapidity of development. GFS proposes the formation of a small storm this weekend, while CEP and UKMO see rather the formation of an ill defined broad circulation. However, the signal within the European ensem
ble forecast has increased recently.

The likelihood for the development of a moderate tropical storm near Diego-Garcia is becoming very low from Saturday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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053
AWIO20 FMEE 151129

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/15 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The South-West Indian Ocean remains in a kind of near-equatorial trough (NET) pattern with an equatorial westerly flow displaced into the northern hemisphere around 7N, and a NET centered around 2-3S between 65 and 80E, towards which the south-hemispheric trade winds flow converges. Convective activity is busy in the vicinity of this TPE, near the equator between 65 and 85E, and in the North Indian Ocean, particularly near a developing TC west of the Indian coast, which is monitored by RSMC New Delhi.

Within the convective activity associated with the NET on the southern hemispheric side, a more active area is present south of the Maldives, in the slowing of the trade winds between 70 and 78E. An emerging low-pressure circulation can be detected there, located around 2.8S/74.5E (south south-east of Gan), better defined than the day before with yet an elongated and asymmetrical structure and winds reaching 20/25kt in the southwest quadrant 10/15kt elsewhere, according to the lmast night HY2 data.

This active basin pattern which has organized somehow symmetrically on either side of the near-equatorial westerly wind burst is largely related to the significant equatorial wave activity that has been ongoing this week (active phase of the MJO, superimposed with a Kelvin wave).

In the SWIO, the circulation we are interested in south south-east of Gan benefits from good surface convergence on the trade winds side and good upper level divergence in a very moist environment. However, the potential for cyclogenesis could be limited by several factors : the presence of a moderate northeasterly shear, its position still close to the equator

and the weakness of the trans-equatorial flow.

In this context, NWP models suggest various scenarios, all of which go for more or less important strengthening of this low-pressure circulation and its gradual motion away from the equator, moving southward and tracking near the Chagos archipelago (Diego Garcia) between Sunday and Monday.

At this stage, the system will com closer the axis of the upper ridge, maintaining a good polar convergence. It could benefit from a window of intensification between Tuesday and Thursday, before undergoing strong vertical north-westerly wind shear from Thursday. The intensities proposed by the deterministic models are now globally comparable, and the signal of the IFS ensemble forecast is increasing significantly, becoming moderate from Monday.

The risk of formation of a moderate tropical storm, low to moderate in the vicinity of the Chagos on Sunday, becomes moderate from Monday .

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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767
AWIO20 FMEE 160959

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/16 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The Southwest Indian Ocean has a trade wind pattern west of 70oE and a large area of low pressure east of this boundary within which a low pressure circulation is detectable. The 0402UTC ASCAT swath allows to estimate a circulation between poorly defined in the northern part and winds of about 30kt in the southwest quadrant by gradient effect. At 09UTC, the center of circulation is localizable towards 5.5S/75.5E under a burst of convection. The strong convective activity over the basin is mainly concentrate
d close to this circulation and more spread out at the eastern limit of our basin.

Currently in an unfavorable sheared environment, the circulation will move over the next two days into an area where the shear is more favorable. A 48 hour window for intensification is expected which will allow the circulation to consolidate. Winds of around 35kt are possible in the southern sector of the circulation due to the gradient effect with the high pressure present further south. Then on Tuesday, the wind shear and the intrusion of dry air should hinder the continuation of the intensification leav
ing the system close to the threshold of moderate tropical storm.

The risk of formation of a moderate tropical storm is moderate from Tuesday.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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560
AWIO20 FMEE 171109

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/17 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


Within the near-equatorial area, a wide clockwise circulation lies over the center of the basin, generated by the tropical wave activity over the last days. Convection is concentrated within this area but it significantly weakened since this morning, following the diurnal cycle. Sat animations suggest a closed clockwise circulation but wtill ill-defined on its northern semi-circle, centered in the South-East of the Chagos archipelago near 7.5S/73.3 at 09Z. Wind is estimated at 25kt within the southern semi-
circle.

From tomorrow afternoon and until Wednesday night, the weak system will encounter conducive upper conditions : no wind shear and a moderate upper divergence, especially on the polar side. However, mid-level dry air and a clear lack of equatorward low-level convergence should hinder the consolidation of a symmetrical circulation. The last model runs thus suggest a decrease in their estimated cyclogensis risk.

Thursday, a strong North-Westerly shear quickly sets up ahead of a mid-latitudes upper trough. This trough should interacts with the South-Eastern tip of the low-pressure area and lead to the formation of a baroclinic low in the South-East of Rodrigues island and North of 25S.

The risk of formation of a moderate tropical storm is low from Tuesday until Wednesday night in the South-West of the Chagos archipelago.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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855
AWIO20 FMEE 181200

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/18 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


In the near-equatorial area, the area of low pressure monitored over the last few days is now in the form of a large Area of Disturbed Weather stretched between 11S/63E and 13S/72E. Satellite animations, the latest scatterometer passes and the CIMSS vorticity analyses at 850 hPa show that 2 areas of preferential vorticity exist at each end of this low pressure system. Convective activity is essentially present in the easternmost zone within the deepest warm and humid air. Winds are estimated at 25/30 kt on
the southern edge of this Area of Disturbed Weather.

The current lack of low levels convergence has been the main detrimental factor of development during the last 24 hours. This will become even more pronounced tomorrow with an interaction with a mid-latitude trough that will weaken the low-level convergence on the south side and drain southwards a large part of the humid tropical air associated with the easternmost vorticity zone. This warm advection will participate in the second part of the week to a cyclogenesis with mainly baroclinic characteristics in
the South-East of the Mascarene Islands between 20S and 30S. From the initial Disturbed Zone, only the westernmost vortex will remain, which will have no potential to develop in an environment that is too dry in the middle troposphere and sheared.

There is no longer any risk of a moderate tropical storm forming over the basin during the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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251
AWIO20 FMEE 191146

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/19 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The two lows monitored since the last days in the near equatorial area, are still visible in classical imagery at 10Z. The convective activity within this large low pressure area is weak but still depict a signature in the CIMMS analysis products (MIMIC TPW and vorticity at 850 hPa and to a lesser extent at 700 hPa). However, the current environmental conditions are unconducive for triggering a cyclogenesis process, due in particular to a weak low-level convergence. Aloft, the wind shear that is currently p
resent (and is being strengthened) is also a factor limiting digging in the medium term. The 0327Z scatterometric swath depicts in particular an elongated and poorly defined circulation at 350 NM East of Agalega, with winds estimated at 25kt maximum by gradient effect, in the southern quadrant, far from the lower level circulation center. The signals in analysis for the easternmost vortex are relatively weak and poor.

No improvement expected for the environmental conditions in the next few days. The low level convergence will not be able to initiate, and will even be hindered by an interaction with a mid-latitude trough that will weaken the low level convergence on the south side and drain on the polar side, a large part of the humid tropical mass air associated with the easternmost vortex area. This warm advection will trigger in the second part of the week to a cyclogenesis with mainly baroclinic characteristics in the
South-East of the Mascarene archipelago, between 20S and 30S. From the initial Disturbed Zone in the near equatorial area, only the westernmost vortex will remain, which will have no potential to develop in an environment becoming drier in the middle troposphere and sheared.

There is no longer any risk of a moderate tropical storm forming over the basin during the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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474
AWIO20 FMEE 201146

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/20 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


Convective activity over the SWIO basin is mainly organized within the broad low pressure area present over the center of the basin in which we can still distinguish two main areas of vorticity, remnant from the same initial low pressure area that has been monitored by the RSMC for several days. There is also marginal thunderstorm activity over the northeast of the basin in an area of slowing trade winds.

Of both of these vorticity aeras, the northernmost one was centered at 10Z around 9.3S/62.6E (east of Agalega), with a fairly broad surface circulation, out of phase and east of its convection and with winds reaching 20 to 25kt. The southernmost and less well-defined vorticity area was centered at 10Z around 18.2S/66.6E (east of Rodrigues), associated with weak convection and more or less merging into a frontal boundary. Other weak and small vorticity areas even seem to appear also on satellite imagery with
in the convergence line that connects the two main areas.

Environmental conditions forecast in the short run are rather unconducive for tropical cyclogenesis initiation from these vorticity areas, due to insufficient low-level convergence and the increasing presence of vertical wind shear over that area. The southernmost vorticity area is expected to interact with a mid-latitude trough, triggering a predominantly baroclinic cyclogenesis by Saturday. The tightening of the pressure gradient on the polar side should allow a strengthening of the trade wind flow up to
35 or even 40 kt in the southern semicircle of the circulation (which is expected Saturday between 24S and 27S and between 64E and 68E), but with a LLC that seems to remain rather elongated and to struggle to become closed according to most models and with a low pressure that would fail to form a deep warm core due to the dry mid-tropospheric advection that should slow down the onset of subtropical development. In addition, this cyclogenesis should diminish the poleward con
vergence
of the other circulation located further north (which will evolve this weekend between 11S and 16S and between 64E and 69E), which adds another unfavorable factor to development.

There is no significant risk of development of a moderate tropical storm during the next 5 days over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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841
AWIO20 FMEE 221114

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/22 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The convective activity of the basin is mainly located close to the low pressure area over the center of the basin, in which two main vorticity spots can still be distinguished, coming from the same initial Area of Disturbed Weather monitored by the RSMC for several days.

Among the two main vorticity areas, the northernmost one was centred at 10Z around 10S/68E (east of Agalega), with a fairly broad and weak surface circulation, the associated convection remains fragmented and strongly north-easterly sheared, associated winds reaching 20kt far from the center in the southern semi-cercle. Further south, due to baroclinic interaction with an upper trough, two minima exist around a barycentre located around 24.8S/67.7E. The winds reach gale force in the southern semicircle o
f this broad circulation in the pressure gradient.

Regarding the first minimum, with the decrease of the polar surface convergence, and the persistence of a north-easterly upper level constraint, no significant deepening is expected. This area should fill up at the end of the weekend.

For the second minimum, the initiation of a tropical transition remains very unlikely because of strong westerly shear that should remain present. However, within the pressure gradient in the southern part, the wind gale force could remain until the next night, then gradually weaken.. This minimum should also disappear at the beginning of the week.

There is no significant risk of development of a moderate tropical storm during the next 5 days over the basin.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
$$
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804
AWIO20 FMEE 231108

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/23 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The thunderstorm activity over the basin is still organized within an area of low pressure longitudinally axed between 7oS and 29oS between 65oE and 70oE.

The southern part of this axis is occupied by a low-pressure system that keeps its non-tropical characteristics. It will evacuate South-eastwards from tomorrow.

The northern part, extending between 7oS and 15oS, is occupied by a surface to low levels trough. The thunderstorm activity has increased compared to yesterday on the southern part of this axis in a weakly sheared environment. However, the low levels convergence within this trough structure coupled with a baroclinic environment (strong temperature and humidity contrast between the eastern and western sides of the trough), leave no potential for tropical cyclogenesis in the next few days.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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890
AWIO20 FMEE 241051

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/24 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


Convective activity is weak over the basin, and remains mainly observed around two weak low-pressure areas on either side of the axis 9S 66E - 18S - 66E.

The low in the south of this axis will keep non-tropical characteristics and should gradually fill in on the northern edge of the ridge, coming from the west. North of this axis, in the tropical field, the large low-pressure area centered between 6oS and 14oS, is nested within a large surface trough, in which it will gradually dissolve during the next 24 hours, mainly due to a lack of low level convergence. Moreover, the upper environmental conditions will remain unconducive for a new cyclogenesis.

Development of a moderate tropical storm is not expected for the next 5 days.



NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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137
AWIO20 FMEE 250926

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/25 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


No significant convective activity over the basin.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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643
AWIO20 FMEE 260458

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2021/05/26 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


No significant convective activity over the basin.

Development of a moderate tropical storm is not expected for the next 5 days.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low: less than 10% Moderate: 30% to 60% Very high: over 90%
Low: 10% to 30% High: 60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.
&&
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