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From: <ldm@weather.cod.edu>
Subject: Indian-S: RSMC La Reunion Tropical Cyclone Analysis
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Message-ID: <20220225121443.1837D1C0087@weather.cod.edu>
Date: Fri, 25 Feb 2022 12:14:42 +0000
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575 
AWIO20 FMEE 251205

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

BULLETIN FOR CYCLONIC ACTIVITY AND SIGNIFICANT TROPICAL WEATHER IN
THE SOUTHWEST INDIAN OCEAN

DATE: 2022/02/25 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:

The monsoon flow is established over the whole basin and feeds a monsoon trough (MT) centered between 15S and 11S from west to east.

The western part of the MT (west of 70E) is rather diffuse and poorly defined, partly due to the presence of the post-tropical depression ex-EMNATI south of Madagascar that strongly disrupts convergence on the polar side of the MT. Convection is organized in a scattered way in various convergence bands on the edge of the MT. A low-pressure circulation is visible around 14S/66E accompanied by deep convection but does not have chances of development because of lack of convergence and disruption from dry air.

Ex-EMNATI has been post-tropical since yesterday and continues its slow evacuation towards the mid-latitudes without presenting any threat for inhabited lands.
Post-Tropical Depression Ex-EMNATI :

Position at 10UTC : 32.8S / 41.8E

Movement : south-southeast at 15 kt

Maximum winds averaged over 10 minutes : 50 kt

Estimated central pressure : 989 hPa

Over the eastern part of the basin and into the Australian area of responsibility, convergence within the MT is particularly good both on the equatorial and polar sides, helped by the presence of a subtropical high over the southeast of the basin. This convergence and convective activity is also enhanced by conducive equatorial wave activity over the eastern part of the basin with the passage of an Equatorial-Rossby wave within an active phase of the MJO. This conducive context has led to the formation of two tropical systems near 90E, including a more developed system east of 90E which reached moderate tropical storm status last night and then severe tropical storm stage this Friday and was named VERNON by the Australian weather service (on the BoM classification, VERNON is a category 2 cyclone, which is equivalent to a severe tropical storm in our basin). The other system is much weaker and was located around 11.9S/88.6E at 10UTC and can be analyzed as a Zone of Disturbed W
 eather w
 ith winds estimated at 25 kt.

Severe Tropical Storm VERNON (east of 90E)

Position at 06UTC : 13.7S / 94.4E

Movement : west-southwest at 8 kt

Maximum winds averaged over 10 minutes : 55 kt

Estimated central pressure : 989 hPa
For more information on this system, please refer to BoM's IDW27700 bulletin.

VERNON benefits from conducive conditions in the short term and should, according to BoM's forecasts, enter the South-West Indian Ocean basin (west of 90E) at a severe tropical storm stage from tomorrow Saturday. RSMC Reunion Island will most probably start monitoring VERNON this Saturday. Once in our basin, VERNON could remain a mature system, but its south-westward track should keep it in the middle of the ocean, far from inhabited lands.

The risk of Severe Tropical Storm VERNON entering our eastern basin from the Australian area of responsibility is very high (>90%) starting tomorrow (Saturday, February 26). This system does not pose any threat for inhabited lands.

Zone of Disturbed Weather near 90E

The Zone of Disturbed Weather which was located this Friday 10UTC around 11.9S/88.6E is expected to interact with VERNON near 90E, with the two systems rotating around each other ("Fujiwhara effect") on Saturday. Although VERNON should prevail and end up absorbing this vortex by Sunday, some deterministic scenarios allow enough time for it to develop into a moderate tropical storm near 90E (with a possible brief hello/goodbye east of 90E), but the dominant scenario still favours a fairly weak system, hindered by the presence of VERNON, which would then disappear by absorption into VERNON's circulation by Sunday.

There is a small risk of another new moderate tropical storm forming briefly near the eastern border of the basin this weekend.

NOTA BENE: The likelihood is an estimate of the chance of the genesis of a moderate tropical storm over the basin and within the next five days:

Very low:       less than 10%              Moderate:        30% to 60%        Very high:      over 90%
Low:             10% to 30%                  High:               60% to 90%

The Southwestern Indian Ocean basin extends from the equator to 40S and from the african coastlines to 90E.

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