SIO: CHENGE - Moderate Tropical Storm

[Subtrop]

94S INVEST 251016 0000 6.0S 74.3E SHEM 15 1009

[Subtrop]

WTIO30 FMEE 190050
RSMC / TROPICAL CYCLONE CENTER / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER: 7/4/20252026
1.A MODERATE TROPICAL STORM 4 (CHENGE)

2.A POSITION 2025/10/19 AT 0000 UTC:
WITHIN 30 NM RADIUS OF POINT 8.5 S / 70.8 E
(EIGHT DECIMAL FIVE DEGREES SOUTH AND
SEVENTY DECIMAL EIGHT DEGREES EAST)
MOVEMENT: WEST-SOUTH-WEST 13 KT

3.A DVORAK ANALYSIS: 3.0/3.0/D 0.5/18 H

4.A CENTRAL PRESSURE: 998 HPA
5.A MAX AVERAGE WIND SPEED (10 MN): 35 KT
RADIUS OF MAXIMUM WINDS (RMW): NIL

6.A EXTENSION OF WIND BY QUADRANTS (KM):
28 KT NE: 0 SE: 610 SW: 435 NW: 230
34 KT NE: 0 SE: 240 SW: 240 NW: 10

7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1009 HPA / 800 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: DEEP

1.B FORECASTS (WINDS RADII IN KM):
12H: 2025/10/19 12 UTC: 8.8 S / 69.1 E, VENT MAX= 040 KT, MODERATE TROPICAL
STORM
28 KT NE: 0 SE: 520 SW: 490 NW: 100
34 KT NE: 0 SE: 350 SW: 285 NW: 0

24H: 2025/10/20 00 UTC: 8.9 S / 68.1 E, VENT MAX= 040 KT, MODERATE TROPICAL
STORM
28 KT NE: 240 SE: 715 SW: 610 NW: 285
34 KT NE: 0 SE: 360 SW: 325 NW: 0

36H: 2025/10/20 12 UTC: 9.0 S / 67.5 E, VENT MAX= 040 KT, MODERATE TROPICAL
STORM
28 KT NE: 260 SE: 520 SW: 520 NW: 250
34 KT NE: 10 SE: 175 SW: 305 NW: 0

48H: 2025/10/21 00 UTC: 9.2 S / 66.6 E, VENT MAX= 040 KT, MODERATE TROPICAL
STORM
28 KT NE: 195 SE: 465 SW: 465 NW: 325
34 KT NE: 0 SE: 0 SW: 195 NW: 205

60H: 2025/10/21 12 UTC: 9.3 S / 65.8 E, VENT MAX= 035 KT, MODERATE TROPICAL
STORM
28 KT NE: 195 SE: 335 SW: 555 NW: 405
34 KT NE: 0 SE: 35 SW: 220 NW: 195

72H: 2025/10/22 00 UTC: 9.4 S / 64.8 E, VENT MAX= 035 KT, MODERATE TROPICAL
STORM
28 KT NE: 155 SE: 155 SW: 215 NW: 155
34 KT NE: 0 SE: 0 SW: 155 NW: 0

2.B LONGER-RANGE OUTLOOK:
96H: 2025/10/23 00 UTC: 9.6 S / 63.1 E, VENT MAX= 035 KT, MODERATE TROPICAL
STORM
28 KT NE: 315 SE: 315 SW: 315 NW: 315
34 KT NE: 0 SE: 140 SW: 140 NW: 20

120H: 2025/10/24 00 UTC: 9.4 S / 60.3 E, VENT MAX= 030 KT, TROPICAL DEPRESSION
28 KT NE: 280 SE: 280 SW: 280 NW: 280

2.C ADDITIONAL INFORMATION:
T=CI=3

OVER THE PAST 6 HOURS, CONVECTIVE ACTIVITY HAS INCREASED SIGNIFICANTLY
AND THE SYSTEM HAS BEGUN TO TRANSITION TO A CURVED BAND
CONFIGURATION. DVORAK'S SUBJECTIVE ANALYSIS SUGGESTS AN UPGRADE TO T 3
WITH ESTIMATED WINDS OF AROUND 35KT. THE SYSTEM HAS BEEN RECLASSIFIED
AS A TROPICAL STORM AND WAS NAMED CHENGE AT 00UTC BY THE MAURITIUS
WEATHER SERVICE.

THE SYSTEM'S TRACK REMAINS WEST-SOUTHWEST, GUIDED BY THE SUBTROPICAL
RIDGE IN THE MIDDLE AND LOWER TROPOSPHERE SOUTH OF THE SYSTEM.
SUBSEQUENTLY, THE MID-TROPOSPHERE RIDGE IS EXPECTED TO CONTINUE TO
STRENGTHEN AND MAINTAIN THIS TRACK. THE CMRS FORECAST IS BASED ON A
COMPROMISE BETWEEN THE BEST GUIDANCES AVAILABLE, BUT IT SHOULD BE
NOTED THAT THE DISPERSION INCREASES QUITE RAPIDLY FROM 72 HOURS
ONWARDS, WITH SCENARIOS MOVING FURTHER NORTHWARD.

IN TERMS OF INTENSITY FORECAST, THE SYSTEM COULD INTENSIFY SLIGHTLY
OVER THE NEXT 24 HOURS. LOWER-LEVEL CONVERGENCE WILL CONSOLIDATE,
ALLOWING THE SYSTEM TO RESIST WIND SHEAR THAT IS STRENGTHENING AGAIN
AT ALTITUDE, WHILE REMAINING MORE MODEST IN THE MID-TROPOSPHERE. NOTE
THAT THIS SHEAR IS MUCH MORE SIGNIFICANT NORTH OF THE TRAJECTORY,
LEAVING A HIGH DEGREE OF UNCERTAINTY IN THE INTENSITY FORECAST
DEPENDING ON THE TRAJECTORY FORECAST. HOWEVER, THE ENVIRONMENT
REMAINS FAVORABLE FOR IT TO REMAIN A MODERATE TROPICAL STORM OVER THE
NEXT 3 TO 4 DAYS BEFORE WEAKENING DUE TO A SUPPLY OF DRYER AIR FROM THE
POLAR REGION.

NO SIGNIFICANT IMPACT IS EXPECTED FOR INHABITED AREAS OVER THE NEXT 72
HOURS.