AWIO20 FMEE 061109
TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2026/05/06 A 1200 UTC

PART 1: WARNING SUMMARY

NIL.

PART 2 : TROPICAL WEATHER DISCUSSION:

The basin displays a Near-Equatorial Trough (NET) pattern east of 65oE. Convective activity is moderate on either side of the NET and near the Seychelles. Most notably, it is locally intense near a disturbed area located in the far northeast of the basin.

Over the next five days, the southwestern Indian Ocean will be affected by an active phase of the MJO, which is gradually shifting eastward. By the end of the week, the cyclonic anomaly associated with a Rossby wave will move from the eastern part of the basin toward the center along the NET. It will maintain vorticity in the current area of disturbed weather.

Suspect area over the northeastern part of the basin :
An increase in convective activity is observed on the southern side of a large low-pressure system, the center of which appears to be located near 6.5oS/83.5oE, according to recent satellite imagery. No conclusive ASCAT data is available so far today. A convective curve can be discerned in the 89 GHz image from the METOP-03 AMSU swath at 0341 UTC.
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, given that moderate northeasterly wind shear remains present over the area and that a twin cyclogenesis event in the Northern Hemisphere could compete with it and limit convergence over the equatorial region. The European deterministic model does not appear to support the development of a moderate tropical storm (MTS), which is in complete disagreement with its American counterpart, the GFS, which forecasts cyclogenesis as early as May 8. The reason is an injection of dry air into the upper and middle troposphere, which is simulated by IFS but not by GFS. Given the current state of the models, it is difficult to make a definitive forecast.
Regarding the ensemble models, many EPS and GEFS members forecast a transition to MTS, though with a less clear signal on the European side. The AI deterministic models no longer reach the MTS stage, and the AI ensembles are becoming less and less responsive.

The risk of tropical storm development over the northeast of the basin becomes low from Friday May 8th.



10-day outlook:
10-day outlook :
The interaction between the Rossby wave and a Kelvin wave appears to be delayed compared to recent days and is expected to occur in the middle of next week. It remains to be determined whether this could contribute to triggering late cyclogenesis within the suspect area mentioned above.

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.