WTIO30 FMEE 081832
RSMC / TROPICAL CYCLONE CENTER / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER: 11/3/20202021
1.A SEVERE TROPICAL STORM 3 (BONGOYO)

2.A POSITION 2020/12/08 AT 1800 UTC:
WITHIN 20 NM RADIUS OF POINT 18.5 S / 76.7 E
(EIGHTEEN DECIMAL FIVE DEGREES SOUTH AND
SEVENTY SIX DECIMAL SEVEN DEGREES EAST)
MOVEMENT: WEST-SOUTH-WEST 12 KT

3.A DVORAK ANALYSIS: 3.5/3.5/S 0.0/6 H

4.A CENTRAL PRESSURE: 988 HPA
5.A MAX AVERAGE WIND SPEED (10 MN): 55 KT
RADIUS OF MAXIMUM WINDS (RMW): 28 KM

6.A EXTENSION OF WIND BY QUADRANTS (KM):
28 KT NE: 95 SE: 185 SW: 150 NW: 95
34 KT NE: 55 SE: 95 SW: 95 NW: 55
48 KT NE: 45 SE: 45 SW: 50 NW: 0

7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1009 HPA / 700 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: DEEP

1.B FORECASTS (WINDS RADII IN KM):
12H: 2020/12/09 06 UTC: 19.7 S / 75.9 E, VENT MAX= 050 KT, SEVERE
TROPICAL STORM
28 KT NE: 75 SE: 150 SW: 65 NW: 110
34 KT NE: 65 SE: 95 SW: 55 NW: 65
48 KT NE: 55 SE: 55 SW: 45 NW: 45

24H: 2020/12/09 18 UTC: 20.2 S / 75.4 E, VENT MAX= 040 KT, MODERATE
TROPICAL STORM
28 KT NE: 65 SE: 120 SW: 75 NW: 75
34 KT NE: 55 SE: 95 SW: 55 NW: 65

36H: 2020/12/10 06 UTC: 20.5 S / 73.9 E, VENT MAX= 030 KT, TROPICAL
DEPRESSION
28 KT NE: 30 SE: 95 SW: 130 NW: 65

48H: 2020/12/10 18 UTC: 20.3 S / 71.9 E, VENT MAX= 030 KT, REMNANT
LOW
28 KT NE: 30 SE: 100 SW: 110 NW: 55

60H: 2020/12/11 06 UTC: 20.5 S / 69.5 E, VENT MAX= 025 KT, REMNANT
LOW

72H: 2020/12/11 18 UTC: 20.8 S / 66.3 E, VENT MAX= 025 KT, REMNANT
LOW

2.B LONGER-RANGE OUTLOOK:
NIL


2.C ADDITIONAL INFORMATION:
T=CI=3.5+

IN THE LAST 6 HOURS, CONVECTIVE ACTIVITY MAINTAINED NEAR BONGOYO
CENTER. MICROWAVE IMAGES (ESPECIALLY 1312Z SSMIS) SHOW THAT DEEP
CONVECTION IS STILL CONCENTRATED IN THE SOUTHWESTERN SEMICIRCLE OF
THE SYSTEM. THIS ASYMMETRY IS PROBABLY RELATED TO THE
MID-TROPOSPHERIC SHEAR ANALYZED BY CIMSS AROUND 20KT FROM NORTH. THE
LATEST SMAP AND ASCAT PASSES SHOW LITTLE EVOLUTION COMPARED TO THOSE
OF 12 HOURS AGO. THE INTENSITY IS THUS MAINTAINED AT 55KT.

BONGOYO SEEMS AT THE END OF ITS DEEPENING PHASE AS THE FAVORABLE
CONDITIONS WINDOWS IS CLOSING IN. INDEED, THE DEEP VERTICAL SHEAR
SHOULD INCREASE RAPIDLY IN THE NEXT HOURS AND BE ASSOCIATED WITH MORE
EFFCIENT DRY INTRUSIONS. WITH A RAPIDLY DILUTING WARM CORE, THE
SYSTEM IS THUS EXPECTED TO GRADUALLY WEAKEN INTO A RESIDUAL
DEPRESSION.

UNDER THE INFLUENCE OF THE MID-LEVEL SUBTROPICAL RIDGE, THE STORM
SHOULD KEEP ON HEADING SOUTH-WESTWARD OVER THE NEXT HOURS. TOMORROW,
THE STEERING FLOW SHOULD COME DOWN TO LOWER LEVELS DUE TO THE
WEAKENED STATE OF THE SYSTEM. BONGOYO IS THUS EXPECTED TO DRIFT
GENERALLY WESTWARD ON THE NORTHERN SIDE OF THE SUBTROPICAL HIGH
PRESSURE AREA.

UNDER A VERY ATTENUATED FORM THIS WEEK-END, THE RESIDUAL LOW BONGOYO
SHOULD NOT HAVE A SIGNIFICANT IMPACT IN TERMS OF WIND AND RAINFALL
OVER THE INHABITED ISLANDS.
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