WTIO30 FMEE 281822
RSMC / TROPICAL CYCLONE CENTER / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER: 21/4/20202021
1.A MODERATE TROPICAL STORM 4 (CHALANE)

2.A POSITION 2020/12/28 AT 1800 UTC:
WITHIN 20 NM RADIUS OF POINT 19.8 S / 41.5 E
(NINETEEN DECIMAL EIGHT DEGREES SOUTH AND
FORTY ONE DECIMAL FIVE DEGREES EAST)
MOVEMENT: WEST 9 KT

3.A DVORAK ANALYSIS: 2.5/2.5/D 0.5/12 H

4.A CENTRAL PRESSURE: 999 HPA
5.A MAX AVERAGE WIND SPEED (10 MN): 35 KT
RADIUS OF MAXIMUM WINDS (RMW): 65 KM

6.A EXTENSION OF WIND BY QUADRANTS (KM):
28 KT NE: 280 SE: 130 SW: 75 NW: 220
34 KT NE: 55 SE: 55 SW: 0 NW: 55
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): 1007 HPA / 400 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: DEEP

1.B FORECASTS (WINDS RADII IN KM):
12H: 2020/12/29 06 UTC: 19.8 S / 40.2 E, VENT MAX= 045 KT, MODERATE
TROPICAL STORM
28 KT NE: 305 SE: 215 SW: 215 NW: 260
34 KT NE: 150 SE: 95 SW: 100 NW: 130

24H: 2020/12/29 18 UTC: 19.5 S / 38.1 E, VENT MAX= 055 KT, SEVERE
TROPICAL STORM
28 KT NE: 325 SE: 230 SW: 215 NW: 260
34 KT NE: 155 SE: 110 SW: 110 NW: 130
48 KT NE: 65 SE: 65 SW: 65 NW: 55

36H: 2020/12/30 06 UTC: 19.4 S / 35.6 E, VENT MAX= 065 KT, TROPICAL
CYCLONE
28 KT NE: 350 SE: 250 SW: 215 NW: 250
34 KT NE: 175 SE: 140 SW: 120 NW: 130
48 KT NE: 75 SE: 85 SW: 75 NW: 75
64 KT NE: 65 SE: 75 SW: 45 NW: 55

48H: 2020/12/30 18 UTC: 19.5 S / 33.2 E, VENT MAX= 030 KT, OVERLAND
DEPRESSION
28 KT NE: 370 SE: 270 SW: 215 NW: 250

60H: 2020/12/31 06 UTC: 18.7 S / 30.6 E, VENT MAX= 025 KT, OVERLAND
DEPRESSION


2.B LONGER-RANGE OUTLOOK:
NIL


2.C ADDITIONAL INFORMATION:

DURING THE LAST 6 HOURS, THE CHALANE CLOUD PATTERN WAS ORGANIZED IN A
CURVED BAND LEAVING A WIND ESTIMATE OF 35KT ACCORDING TO THE DVORAK
ANALYSIS. WITH THIS THRESHOLD, CHALANE IS CLASSIFIED AS A MODERATE
TROPICAL STORM AT 18UTC. THE CONVECTIVE ACTIVITY IS MAINLY LOCATED IN
THE NORTHEAST SEMI-CIRCLE. THE ABSENCE OF RECENT ASCAT SWATH DATA
DOES NOT ALLOW TO VALIDATE THIS ESTIMATE AND THE ASYMMETRY OF WINDS
OBSERVED IN THE SOUTH-WEST QUADRANT (NEARLY 12 HOURS AGO) CANNOT BE
LIFTED.

DRIVEN BY THE RIDGE OF LOW AND MEDIUM TROPOPHERE INSTALLED ON THE
SOUTH OF THE CHANNEL, CHALANE WILL CONTINUE ITS WESTWARD MOVEMENT
BEFORE REACHING MOZAMBIQUE. THE MODELS ARE IN FAIRLY GOOD AGREEMENT
ON THE DIRECTION BUT THEY DIFFER SOMEWHAT ON THE SPEED OF MOVEMENT.
THE RSMC HAS OPTED FOR A RELATIVELY FAST DISPLACEMENT, ALLOWING THE
METEOR TO LAND IN ABOUT 36 HOURS ON THE MOZAMBICAN COAST, IN
CONNECTION WITH A REGULAR INTENSIFICATION.

THE ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE FOR THE DEVELOPMENT OF
THE SYSTEM: MODERATE SHEAR, FAVORABLE OCEANIC POTENTIAL, GOOD SUPPLY
OF THE MONSOON FLOW WHICH GOES DOWN TO THE MIDDLE OF THE CHANNEL. THE
SCENARIO OF A REGULAR INTENSIFICATION IS THEREFORE TAKEN BY THE RSMC
IN AGREEMENT WITH EUROPEAN NUMERICAL MODELS. CHALANE SHOULD THEREFORE
REACH MOZAMBIQUE AT THE TROPICAL CYCLONE STAGE IN ABOUT 36 HOURS.

ACCORDING TO THIS SCENARIO, THE THREAT REPRESENTED BY CHALANE IS
REAL, CAUSING STRONG WINDS, HEAVY RAINFALL AS WELL AS CYCLONIC SWELL
AND SURGE PHENOMENA, MAINLY IN THE SOUTH OF THE LANDING AREA. THE
INHABITANTS OF THE REGION AROUND BEIRA, FROM THE CITY OF CHINDE IN
THE NORTH AND INHASSORO IN THE SOUTH, ARE INVITED TO KEEP THEMSELVES
INFORMED OF THE EVOLUTION OF THE SITUATION
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