WTIO30 FMEE 270008
RSMC / TROPICAL CYCLONE CENTER / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER: 19/4/20202021
1.A OVERLAND DEPRESSION 4 (CHALANE)

2.A POSITION 2020/12/27 AT 0000 UTC:
WITHIN 20 NM RADIUS OF POINT 17.8 S / 49.2 E
(SEVENTEEN DECIMAL EIGHT DEGREES SOUTH AND
FORTY NINE DECIMAL TWO DEGREES EAST)
MOVEMENT: WEST-SOUTH-WEST 8 KT

3.A DVORAK ANALYSIS: NIL
4.A CENTRAL PRESSURE: 1005 HPA
5.A MAX AVERAGE WIND SPEED (10 MN): 30 KT
RADIUS OF MAXIMUM WINDS (RMW): NIL

6.A EXTENSION OF WIND BY QUADRANTS (KM):
28 KT NE: 0 SE: 140 SW: 0 NW: 0
34 KT NE: 0 SE: 0 SW: 0 NW: 0
48 KT NE: 0 SE: 0 SW: 0 NW: 0
64 KT NE: 0 SE: 0 SW: 0 NW: 0

7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1008 HPA / 600 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: MEDIUM

1.B FORECASTS (WINDS RADII IN KM):
12H: 2020/12/27 12 UTC: 18.3 S / 47.1 E, VENT MAX= 025 KT, OVERLAND
DEPRESSION

24H: 2020/12/28 00 UTC: 19.3 S / 45.1 E, VENT MAX= 020 KT, OVERLAND
DEPRESSION

36H: 2020/12/28 12 UTC: 19.7 S / 43.9 E, VENT MAX= 025 KT, ZONE OF
DISTURBED WEATHER

48H: 2020/12/29 00 UTC: 19.9 S / 42.5 E, VENT MAX= 030 KT, TROPICAL
DEPRESSION
28 KT NE: 10 SE: 35 SW: 100 NW: 55

60H: 2020/12/29 12 UTC: 19.9 S / 40.7 E, VENT MAX= 040 KT, MODERATE
TROPICAL STORM
28 KT NE: 45 SE: 130 SW: 100 NW: 75
34 KT NE: 35 SE: 120 SW: 55 NW: 65

72H: 2020/12/30 00 UTC: 19.8 S / 38.3 E, VENT MAX= 050 KT, SEVERE
TROPICAL STORM
28 KT NE: 55 SE: 140 SW: 85 NW: 75
34 KT NE: 45 SE: 130 SW: 55 NW: 65
48 KT NE: 35 SE: 55 SW: 45 NW: 45

2.B LONGER-RANGE OUTLOOK:
96H: 2020/12/31 00 UTC: 19.5 S / 32.4 E, VENT MAX= 030 KT, OVERLAND
DEPRESSION
28 KT NE: 55 SE: 140 SW: 85 NW: 75

2.C ADDITIONAL INFORMATION:
OVER THE LAST 6 HRS, CHALANE HAS MADE LANDFALL AND IS NOW TRACKING TO
THE NORTH-WEST OF TAMATAVE. THE 1803Z ASCAT-B SWATH SHOWS A
RELATIVELY ATYPICAL STRUCTURE AT THE TIME OF LANDFALL WITH AN OPENING
IN THE NORTH-EASTERN QUADRANT, PROLONGATED BY A SURFACE TROUGH. THIS
DATA ALSO CONFIRMED THE PRESENCE OF NEAR GALE FORCE WINDS WITHIN AT
LEAST THE SOUTHEASTERN QUADRANT. THE WIND ON STE MARIE ISLAND HAS NOW
VEERED NORTH-EASTERLY.

THE MAIN DANGER ASSOCIATED WITH THIS SYSTEM REMAIN THE HEAVY RAINS,
WHICH CAN GENERATE FLASH FLOODS AND WIDESPREAD FLOODS. THESE OCCUR
EVEN FAR FROM THE CENTER IN THE SOUTHERN SECTOR. THUS, MORE THAN
200MM OF RAIN IS EXPECTED OVER THE NEXT 48HRS ON THE EASTERN HIGH
GROUNDS OF THE COUNTRY AS WELL AS CUMULATED RAINFALL RANGING FROM 100
TO 200MM IN THE INTERIOR ALONG CHALANE'S TRACK. THE INHABITANTS OF
THE AREA ARE INVITED TO FOLLOW THE EVOLUTION OF THIS SYSTEM WITH THE
LOCAL AUTHORITIES.

EARLY NEXT WEEK, THE SYSTEM SHOULD COME BACK OVER OPEN WATERS IN THE
MOZAMBIQUE CHANNEL, WHERE ENVIRONMENTAL CONDITIONS APPEAR TO BE
FAVORABLE FOR REINTENSIFICATION AT FIRST (WEAK SHEAR, GOOD UPPER
OUTLFOW, LOW-LEVEL NORTHERLY AND TRADE WIND FLOW FUELING A GOOD
SURFACE CONVERGENCE AND HIGH OCEANIC HEAT CONTENT). A LOW/MID LEVEL
RIDGE OCCUPYING THE SOUTHERN HALF OF THE CHANNEL SHOULD DRIVE A
GENERALLY WESTWARD MOTION OF THE STORM.
GIVEN THE INITIAL STATE OF THE SYSTEM, THE UNCERTAINTY UPON THE
LOCALISATION OF REENTRY OVER WATER AND THE LACK OF AGREEMENT ON THE
POSSIBILITY OF REINTENSIFICATION AMONG THE AVAILABLE GUIDANCE, THERE
IS NOT A STRONG DEGREE OF CONFIDENCE ASSOCIATED WITH THIS SECOND PART
OF THE FORECAST.

LAST WARNING ISSUED ON THIS SYSTEM, BEFORE A POSSIBLE
REINTENSIFICATION OVER THE MOZAMBIQUE CHANNEL.
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