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From: <ldm@weather.cod.edu>
Subject: Indian-S: RSMC La Reunion Tropical Cyclone Analysis
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Date: Mon, 17 Jan 2022 11:56:28 +0000
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931 
AWIO20 FMEE 171151

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2022/01/17 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The trans-equatorial monsoon flow is mainly present west of 70oE. The convergence with the trade wind is not well defined but the configuration of the low level winds allows to define a branch of the Monsoon trough (TM) between 60 and 75oE and from 11oS to 14oS. The convective activity is mainly present near this branch of the TM, between the southeast of Agalega and the Chagos, where it continues to strengthen compared to previous days. The convergence is indeed favored by a push of west to northwest winds on the northern side of the TM in connection with a favorable wave activity, especially the passage of a Kelvin wave.

Another convection zone is located in the Mozambique Channel around 14oS in the convergence of the monsoon flow and a southern flow.

A low-pressure minimum should appear in this TM during the next 48h, between Agalega and Saint-Brandon. However, environmental conditions are not optimal at the beginning of the period, with a moderate easterly shear, dry mid-tropospheric air, and a weak convergence of low layers on the south side. Conditions become more favorable from Thursday and especially at the end of the week with the strengthening of a subtropical ridge southeast of the Mascarenes giving a more assertive trade wind, converging more effectively with a monsoon flow, which also intensifies under the impetus of the equatorial wave activity. At the same time, the air mass should become more humid over the whole layer in the vicinity of this minimum. Under these conditions, the chances of development become more serious at the end of the week over an area located off the northern Mascarene Islands and east of Madagascar. This development scenario is supported by the GEFS and EPS ensemble forecasts as well as
  some de
 terministic scenarios, with probabilities becoming more significant from Friday, suggesting a moderate risk of cyclogenesis at the end of the week. This risk could possibly concern the immediate surroundings of the eastern coast of Madagascar according to some of the scenarios.

In addition, the strengthening of the TM at the end of the week to the center of the basin could promote the emergence of a second area of vorticity located further east, east of 70oE. Some scenarios suggest a development into a storm, from Saturday. There is then a very low risk of tropical storm formation at the very end of the period.

The risk of formation of a tropical storm becomes weak from Thursday then moderate from Friday off or near the east coast of Madagascar and off the northern Mascarene Islands. It is very weak over the east of the basin at the end of the period.


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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