WTIO30 FMEE 191254
RSMC / TROPICAL CYCLONE CENTER / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER: 1/16/20202021
1.A ZONE OF DISTURBED WEATHER 16

2.A POSITION 2021/04/19 AT 1200 UTC:
WITHIN 60 NM RADIUS OF POINT 10.7 S / 57.4 E
(TEN DECIMAL SEVEN DEGREES SOUTH AND
FIFTY SEVEN DECIMAL FOUR DEGREES EAST)
MOVEMENT: WEST 11 KT

3.A DVORAK ANALYSIS: 1.5/1.5/S 0.0/24 H

4.A CENTRAL PRESSURE: 1006 HPA
5.A MAX AVERAGE WIND SPEED (10 MN): 25 KT
RADIUS OF MAXIMUM WINDS (RMW): NIL

6.A EXTENSION OF WIND BY QUADRANTS (KM):
NIL

7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1009 HPA / 200 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: MEDIUM

1.B FORECASTS (WINDS RADII IN KM):
12H: 2021/04/20 00 UTC: 11.3 S / 54.2 E, VENT MAX= 025 KT, TROPICAL
DISTURBANCE

24H: 2021/04/20 12 UTC: 11.0 S / 51.4 E, VENT MAX= 035 KT, MODERATE
TROPICAL STORM
28 KT NE: 0 SE: 370 SW: 315 NW: 0
34 KT NE: 0 SE: 220 SW: 185 NW: 0

36H: 2021/04/21 00 UTC: 10.3 S / 49.1 E, VENT MAX= 045 KT, MODERATE
TROPICAL STORM
28 KT NE: 75 SE: 370 SW: 315 NW: 185
34 KT NE: 75 SE: 220 SW: 185 NW: 75

48H: 2021/04/21 12 UTC: 10.0 S / 47.6 E, VENT MAX= 055 KT, SEVERE
TROPICAL STORM
28 KT NE: 75 SE: 370 SW: 315 NW: 185
34 KT NE: 75 SE: 220 SW: 185 NW: 75
48 KT NE: 0 SE: 35 SW: 35 NW: 20

60H: 2021/04/22 00 UTC: 10.0 S / 46.4 E, VENT MAX= 055 KT, SEVERE
TROPICAL STORM
28 KT NE: 75 SE: 370 SW: 315 NW: 185
34 KT NE: 75 SE: 220 SW: 185 NW: 75
48 KT NE: 0 SE: 35 SW: 35 NW: 20

72H: 2021/04/22 12 UTC: 10.0 S / 45.5 E, VENT MAX= 045 KT, MODERATE
TROPICAL STORM
28 KT NE: 75 SE: 370 SW: 315 NW: 185
34 KT NE: 75 SE: 220 SW: 185 NW: 75

2.B LONGER-RANGE OUTLOOK:
96H: 2021/04/23 12 UTC: 10.1 S / 43.5 E, VENT MAX= 025 KT, FILLING UP

120H: 2021/04/24 12 UTC: 9.3 S / 41.1 E, VENT MAX= 020 KT, FILLING UP

2.C ADDITIONAL INFORMATION:
T=CI=1.5+

THE CIRCULATION THAT HAS BEEN MONITORED SINCE LAST WEEK VIA THE
RSMC'S ITCZ BULLETINS, WHILE CIRCULATING NEAR THE CHAGOS, HAS
EXPERIENCED A TEDIOUS DEVELOPMENT DURING ITS WESTWARD TRACK, IN A TOO
DRY ENVIRONMENT LINKED TO THE DRY PHASE OF THE MJO AND WITH A LACK OF EQUATORWARD CONVERGENCE. HOWEVER, SINCE YESTERDAY SUNDAY AND
ESPECIALLY THIS MONDAY, IT SHOWS SIGNS OF BETTER ORGANIZATION, AS IT
TRACKS OFF THE SOUTHEAST OF AGALEGA. THE CONVECTIVE BANDS CONVERGE
BETTER TOWARDS A MORE DEFINED SURFACE CENTER, WITH DEEP CONVECTION OF
MODERATE INTENSITY ORGANIZED IN A CURVED BAND. THE ASCAT SWATHS OF
THIS MONDAY MORNING INDICATE WINDS OF 25 KT IN THE SOUTHEASTERN
SEMICIRCLE OF THE SYSTEM, SLIGHTLY UP FROM THE PREVIOUS DAYS, BUT
WITH A STRUCTURE THAT REMAINS ASYMMETRIC (SIGNIFICANTLY WEAKER WINDS
IN THE NORTHWESTERN SEMICIRCLE). THE GMI MICROWAVE PASS OF 0715Z
SHOWS THE BEGINNING OF AN ORGANIZATION OF THE SYSTEM.

THERE IS A GOOD AGREEMENT BETWEEN MODELS ABOUT THE SYSTEM'S TRACK
UNTIL WEDNESDAY, WITH A WESTWARD MOVEMENT ON THE NORTHERN SIDE OF THE
LOW TROPOSPHERIC SUBTROPICAL RIDGE, TRACKING IMMEDIATELY SOUTH OF THE
FARQUHAR ATOLL AND OFF NORTHERN MADAGASCAR. FROM WEDNESDAY AND
THURSDAY, WHEN THE SYSTEM WILL REACH THE NORTH OF THE MOZAMBIQUE
CHANNEL AND OFF THE COMOROS, THE STEERING FLOWS BECOME WEAKER AND THE TRAJECTORY IS MORE UNCERTAIN. IN PARTICULAR, THE MORE OR LESS
IMPORTANT INFLUENCE ON THE NORTH OF THE COMOROS ARCHIPELAGO REMAINS
TO BE SPECIFIED.

ENVIRONMENTAL CONDITIONS ARE RELATIVELY FAVORABLE TO SHORT TERM
DEVELOPMENT : IN THE LOW LAYERS, A TRADEWINDS SURGE IS ONGOING,
REINFORCED TOMORROW BY THE ACCELERATION RELATED TO THE BYPASS OF THE
NORTHERN TIP OF MADAGASCAR, WHICH SHOULD INCREASE THE POLEWARD LOW
LEVEL CONVERGENCE. HOWEVER, DURING THIS TIME, THE EQUATORWARD
CONVERGENCE REMAINS WEAK TO VERY WEAK, WHICH BRINGS UNCERTAINTY ON
THE MORE OR LESS EFFICIENT CONSOLIDATION OF THE LOW'S INNER CORE.
ALOFT, DEEP SHEAR IS WEAK AND SHOULD REMAIN SO FOR THE NEXT FEW DAYS
(AROUND 10 KT OR LESS), AND NO INTRUSION OF DRY AIR IN THE
MID-TROPOSPHERE SHOULD INTERFERE WITH CONVECTION NEAR THE CORE OF THE
SYSTEM UNTIL WEDNESDAY. UPPER-TROPOSPHERIC DIVERGENCE IS QUITE GOOD
WITH A LIGHT EQUATORWARD OUTFLOW CHANNEL IN THE SHORT RUN, THEN, FROM
MID-WEEK, AN INCREASE OF UPPER DIVERGENCE ON THE EDGE OF A
SUBTROPICAL TROUGH CIRCULATING FURTHER SOUTH. ON THE OTHER HAND, THE
OCEANIC POTENTIAL IS PRESENT WITH SST AROUND 28-29C AND A GRADUAL
INCREASE OF THE DEPTH OF THE ISO-26C, BECOMING HIGHER IN THE NORTH OF
THE MOZAMBIQUE CHANNEL. THUS, CONDITIONS SEEM TO BE GATHERED FOR
MODERATE INTENSIFICATION UNTIL WEDNESDAY, PROBABLY UNTIL THE STAGE OF
A MODERATE TROPICAL STORM OR EVEN SEVERE TROPICAL STORM. FROM
THURSDAY, THE INCREASE OF THE NORTH TO NORTH-WESTERLY SHEAR ALONG A
TROUGH PASSING OVER THE SOUTH OF MADAGASCAR SHOULD TILT THE
CONVECTIVE CORE AND WEAKEN IT BY ADVECTING DRY AIR. THIS SHOULD LEAD
TO THE WEAKENING OF THE SYSTEM IN THE SECOND PART OF THE WEEK.
THE SMALL SIZE OF THE LOW'S CORE, MAKING IT VERY REACTIVE TO ITS
ENVIRONMENT, INDUCES A HIGHER THAN AVERAGE UNCERTAINTY ON THE PRESENT
INTENSITY FORECAST.
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