WTIO30 FMEE 181205
RSMC / TROPICAL CYCLONE CENTER / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER: 5/8/20202021
1.A MODERATE TROPICAL STORM 8 (JOSHUA)

2.A POSITION 2021/01/18 AT 1200 UTC:
WITHIN 20 NM RADIUS OF POINT 19.5 S / 86.4 E
(NINETEEN DECIMAL FIVE DEGREES SOUTH AND
EIGHTY SIX DECIMAL FOUR DEGREES EAST)
MOVEMENT: WEST 7 KT

3.A DVORAK ANALYSIS: 2.5/3.0/S 0.0/12 H

4.A CENTRAL PRESSURE: 994 HPA
5.A MAX AVERAGE WIND SPEED (10 MN): 40 KT
RADIUS OF MAXIMUM WINDS (RMW): NIL

6.A EXTENSION OF WIND BY QUADRANTS (KM):
28 KT NE: 75 SE: 110 SW: 110 NW: 45
34 KT NE: 55 SE: 75 SW: 75 NW: 0

7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1005 HPA / 400 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: DEEP

1.B FORECASTS (WINDS RADII IN KM):
12H: 2021/01/19 00 UTC: 19.4 S / 83.9 E, VENT MAX= 035 KT, FILLING UP
28 KT NE: 55 SE: 30 SW: 35 NW: 55
34 KT NE: 45 SE: 20 SW: 30 NW: 35

24H: 2021/01/19 12 UTC: 19.6 S / 81.6 E, VENT MAX= 030 KT, REMNANT
LOW
28 KT NE: 35 SE: 30 SW: 30 NW: 55

36H: 2021/01/20 00 UTC: 20.3 S / 79.2 E, VENT MAX= 025 KT, FILLING UP

48H: 2021/01/20 12 UTC: 21.0 S / 77.2 E, VENT MAX= 020 KT, FILLING UP

60H: 2021/01/21 00 UTC: 21.8 S / 74.7 E, VENT MAX= 020 KT, FILLING UP

72H: 2021/01/21 12 UTC: 22.5 S / 73.7 E, VENT MAX= 020 KT,
DISSIPATING

2.B LONGER-RANGE OUTLOOK:
NIL


2.C ADDITIONAL INFORMATION:
T=2.5; CI=3.0-

THE NORTHWESTERLY UPPER SHEAR CONTINUES TO INCREASE AND CLEARLY
AFFECT JOSHUA'S CLOUD PATTERN. THE SURFACE CIRCULATION CENTER IS NOT
YET VISIBLE BUT REMINAS LOCATED ON THE NORTHWESTERN BORDER OF THE
MAIN CONVECTION. THE 0815Z GMI AND 0747Z AMSR2 MW IMAGES CONFIRMED
THAT THE EROSION OF THE WARM CORE IS UNDER WAY, WITH INTENSE RAINS
ONLY LOCATED WITHIN THE SOUTHEASTERN QUADRANT.

IN TERMS OF TRACK FORECAST, JOSHUA IS UNDER THE INFLUENCE OF THE
WESTERN EXTREMITY OF THE SUBTROPICAL RIDGE CENTERED ON THE WESTERN
PART OF THE AUSTRALIAN BASIN. THE RIDGE IS SHIFTING WESTWARD,
IMPOSING A GLOBALLY WEST-SOUTH-WESTWARD STEERING FLOW. THE GUIDANCE
IS IN GOOD AGREEMENT OVER THIS TRACK, WHICH SHOULD NOT CHANGE MUCH
DURING THE NEXT 48 HOURS. THE ENSEMBLE DISPERSION REMAINS MODERATE.

JOSHUA IS CURRENTLY UNDERGOING A GRADUAL DETERIORATION OF ITS
ENVIRONMENT : THE SHEAR ALREADY LOCATED IN THE UPPER LEVELS WILL
SHORTLY INCREASE IN THE MID-LEVELS. THUS, THE MID-LEVEL DRY AIR
ALREADY PRESENT IN THE WESTERN SECTOR WILL CONTINUE TO GRADUALLY
ERODE THE WARM CORE THUS WEAKENING THE SYSTEM. THE SYSTEM SHOULD THEN
EVOLVE QUITE RAPIDLY INTO A REMNANT LOW. THE AVAILABLE GUIDANCE IS IN
GOOD AGREEMENT ON THIS SCENARIO.
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