WTIO30 FMEE 161253
RSMC / TROPICAL CYCLONE CENTER / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER: 2/11/20202021
1.A TROPICAL DISTURBANCE 11

2.A POSITION 2021/02/16 AT 1200 UTC:
WITHIN 20 NM RADIUS OF POINT 20.8 S / 36.0 E
(TWENTY DECIMAL EIGHT DEGREES SOUTH AND
THIRTY SIX DECIMAL ZERO DEGREES EAST)
MOVEMENT: NORTH-EAST 7 KT

3.A DVORAK ANALYSIS: 1.5/1.5/S 0.0/6 H

4.A CENTRAL PRESSURE: 995 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): 1003 HPA / 1100 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: MEDIUM

1.B FORECASTS (WINDS RADII IN KM):
12H: 2021/02/17 00 UTC: 20.0 S / 36.3 E, VENT MAX= 030 KT, TROPICAL
DEPRESSION
28 KT NE: 75 SE: 100 SW: 75 NW: 85

24H: 2021/02/17 12 UTC: 20.5 S / 37.1 E, VENT MAX= 035 KT, MODERATE
TROPICAL STORM
28 KT NE: 130 SE: 165 SW: 85 NW: 120
34 KT NE: 100 SE: 85 SW: 10 NW: 85

36H: 2021/02/18 00 UTC: 21.7 S / 37.4 E, VENT MAX= 035 KT, MODERATE
TROPICAL STORM
28 KT NE: 110 SE: 150 SW: 85 NW: 120
34 KT NE: 85 SE: 65 SW: 10 NW: 85

48H: 2021/02/18 12 UTC: 22.6 S / 37.2 E, VENT MAX= 040 KT, MODERATE
TROPICAL STORM
28 KT NE: 220 SE: 250 SW: 95 NW: 130
34 KT NE: 140 SE: 150 SW: 30 NW: 110

60H: 2021/02/19 00 UTC: 23.3 S / 37.0 E, VENT MAX= 045 KT, MODERATE
TROPICAL STORM
28 KT NE: 215 SE: 100 SW: 75 NW: 65
34 KT NE: 150 SE: 30 SW: 20 NW: 55

72H: 2021/02/19 12 UTC: 23.9 S / 36.5 E, VENT MAX= 055 KT, SEVERE
TROPICAL STORM
28 KT NE: 150 SE: 270 SW: 315 NW: 85
34 KT NE: 100 SE: 110 SW: 165 NW: 45
48 KT NE: 35 SE: 55 SW: 55 NW: 35

2.B LONGER-RANGE OUTLOOK:
96H: 2021/02/20 12 UTC: 25.4 S / 35.9 E, VENT MAX= 070 KT, TROPICAL
CYCLONE
28 KT NE: 260 SE: 215 SW: 100 NW: 130
34 KT NE: 140 SE: 120 SW: 65 NW: 100
48 KT NE: 65 SE: 45 SW: 55 NW: 45
64 KT NE: 55 SE: 35 SW: 35 NW: 35

120H: 2021/02/21 12 UTC: 28.2 S / 37.5 E, VENT MAX= 080 KT, TROPICAL
CYCLONE
28 KT NE: 285 SE: 195 SW: 85 NW: 140
34 KT NE: 130 SE: 100 SW: 75 NW: 110
48 KT NE: 80 SE: 60 SW: 60 NW: 70
64 KT NE: 70 SE: 60 SW: 60 NW: 60

2.C ADDITIONAL INFORMATION:
T=CI=1.5

THIS AFTERNOON, CONVECTION HAS INTENSIFIED AROUND THE LOW PRESSURE
AREA, WITH THE LOW LEVEL CIRCULATION CENTER LOCATED TO THE SOUTH-EAST
OF THE MAXIMUM OF CONVECTION. WITHOUT ANY HELPFUL MICROWAVE IMAGERY,
IT IS DIFFICULT TO ASSESS HOW MUCH THE LOW LEVEL CIRCULATION HAS
TIGHTENED. THE SYSTEM'S INTENSITY IS KEPT AT 25KT, IN AGREEMENT WITH
THE LATEST ASCAT PASS. THE VERY LOW ENVIRONMENTAL PRESSURES MAKE THE
ESTIMATED CENTRAL PRESSURE MUCH LOWER THAN THE PRESSURE USUALLY
EXPECTED FOR A TROPICAL DISTURBANCE.

THE SYSTEM MOVES NORTHEASTWARD IN THE MOZAMBIQUE CHANNEL AT THE
BEGINNING OF ITS LIFE CYCLE, UNDER THE COMBINED INFLUENCE OF A
LOW-LEVEL SOUTHWARD SURGE ON THE EDGE OF THE SOUTH AFRICAN SURFACE
HIGH AND THE WESTERLY FLOW ESTABLISHED AT ABOUT 700HPA ON THE EDGE OF
THE NEAR-EQUATORIAL RIDGE. THE PRESENCE OF A SECONDARY MINIMUM TO THE
SOUTHEAST OF THE SYSTEM COULD TEMPORARILY INFLUENCE ITS TRACK UNTIL
THURSDAY. FROM THURSDAY, A SUBTROPICAL RIDGE REBUILDS TOWARDS
MADAGASCAR, STEERING THE TRACK MORE SOUTHWARD ON ITS WESTERN SIDE.
WITH THE PERSISTENCE OF A RIDGE OVER SOUTHERN AFRICA, THE SYSTEM MAY
EXPERIENCE CONTRADICTORY INFLUENCES IN TERMS OF STEERING FLOW, WHICH
COULD RESULT IN A RATHER SLOW MOVEMENT. FROM FRIDAY, THE RIDGE ALONG
THE INDIAN OCEAN AND MADAGASCAR COAST STRENGTHENS SOUTHEAST OF THE
SYSTEM, WHICH COULD GIVE A SOUTHWEST COMPONENT TO THE TRACK. AROUND
THIS MEDIAN SCENARIO, GUIDANCE REMAINS VERY SCATTERED. THE
UNCERTAINTY ABOUT THIS FORECAST IS THUS QUITE IMPORTANT. IN
PARTICULAR, LANDFALL ON THE MOZAMBICAN COAST CANNOT BE RULED OUT IN
THE NEXT FEW DAYS.

THE SYSTEM IS CURRENTLY IN LOW SHEAR ENVIRONMENT UNDER THE UPPER
TROPOSPHERE RIDGE. IT IS SURROUNDED BY MOIST AIR AT ALL LEVELS
ALTHOUGH SOME DRY AIR ADVECTION MAY OCCUR ON THE WESTERN SIDE OF
SYSTEM IN THE NEXT 48 HOURS. LOW-LEVEL CONVERGENCE IS GOOD ON ITS
POLAR SIDE DUE TO THE SOUTHERLY WIND SURGE THIS TUESDAY, BUT IS STILL
POOR ON THE NORTHEAST SIDE OF THE SYSTEM, IN THE MOZAMBIQUE CHANNEL,
WHICH WILL KEEP THE CIRCULATION ELONGATED UNTIL WEDNESDAY. FROM
THURSDAY ONWARDS, GUIDANCE SUGGEST A BETTER LOW LEVEL CONVERGENCE IN
AN ENVIRONMENT THAT IS STILL FAVORABLE, WHICH SHOULD HELP ORGANIZE A
MORE COMPACT CORE. FROM THEN ON, STEADIER INTENSIFICATION BECOMES
POSSIBLE. HOWEVER, FROM FRIDAY EVENING SOME EASTERLY SHEAR ASSOCIATED
WITH MID-TROPOSPHERIC DRY AIR ADVECTION COULD LIMIT INTENSIFICATION,
AS DEPICTED BY THE LAST GFS RUN. BUT THIS SCENARIO ISN'T WIDESPREAD
IN THE AVAILABLE GUIDANCE.
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