AWIO20 FMEE 031105
TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2026/05/03 A 1200 UTC

PART 1: WARNING SUMMARY

NIL.

PART 2 : TROPICAL WEATHER DISCUSSION:

The basin exhibits a Near-Equatorial Trough (NET) pattern between 50oE and 70oE. Convective activity is weak on either side of the NET and may be moderate at its eastern end. In addition, there is strong convective activity around a area of disturbed weather located in the far northeast of the basin.

Even though the MJO is active over the basin, current conditions remain unfavorable for cyclogenesis due to a lack of convergence on the equatorial side, which limits vorticity within the NET. By the middle of next week, the arrival of an equatorial Rossby wave cyclonic anomaly from the east of the basin could improve conditions within the NET.

Suspect area over the northeastern part of the basin :
An active convective cluster appears to be forming in the southern part of a large low-pressure area. The dual ASCAT-B and ASCAT-C swathes at 0231 UTC and 0302 UTC reveal a large, ill-defined circulation with average winds, apart from convection, near 20 kt.
In this area, the upcoming passage of the Rossby wave could enhance vorticity. It is difficult to know whether this will be sufficient to initiate a cyclogenesis process, but the GFS model suggests a deepening, while another one occurs in the Northern Hemisphere, symmetrically with respect to the equator, reaching the moderate tropical storm stage as early as May 8th, as do a significant number of runs from the GEFS ensemble model. Its European deterministic and ensemble analogues take a little longer to reach this stage, and we must wait at least until the end of next week, just as in the machine learning-trained models. We therefore temper this risk of early formation.

The likelihood of the formation of a moderate tropical storm becomes low from Friday, May the 8th over the northeastern part of the basin.



10-day outlook:
The westerly surge generated by a Kelvin wave late next week over this part of the basin could enhance equatorial convergence and give a boost to cyclogenesis.

NOTA BENE: The likelihood is an estimate of the chance of genesis of a moderate tropical storm over the basin 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.