274
AWIO20 FMEE 041104

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2021/05/04 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


At the equator, the monsoon flow towards the northern hemisphere begins to dominate the general circulation, especially on the Eastern part of the basin. Convection is mainly triggering within the slowing area of the trade winds near 5S on the Western half of the basin.

South of Madagascar, an initiation of subtropical low is now clearly visible on sat imagery, materialized by a quasi-stationary low-level cloud vortex centered on 29.8S/44.3E at 09Z. Associated convection is rather scattered and mainly located on the South-Eastern quadrant, with moderately cold cloud tops.

This morning 0530Z and 0645Z ASCAT swath showed max winds reaching near gale force 30kt between 30nm to 80nm from the center over the Eastern semi-circle and up to 125 nm on the North-Eastern quadrant. The estimated central pressure is 998hPa. The available phase diagrams suggest a symmetrical but still shallow warm core, which is in good agreement with the observed evolution on the sat images of the last 12 hrs. Dry air remains nested over the center of the circulation and prevents the triggering of the co
nvection (thus hindering the constitution of the warm-core).

From tonight, the upper cut-off low which shielded the circulation from the shear until now is expected to drift South-Eastwards. This shift should leave the system unprotected and a strong West-South-Westerly shear will quickly make the organisation of a mid-level warm-core very unlikely. The clockwise circulation is expected to move East-South-Eastwards over the next days, before merging with a baroclinic cold front by Friday evening.

The risk of formation of a subtropical storm South of Madagascar is thus deemed low tonight and tomorrow, before disappearing from tomorrow evening.

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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246
AWIO20 FMEE 051049

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2021/05/05 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


At the equator, the monsoon flow towards the Northern Hemisphere is temporarily present but still weak.

Convection is concentrated in the slowing down of the trade wind towards 9S.

Southeast of Madagascar, the remnants of the subtropical low are clearly visible on satellite imagery, materialized by a vortex of low-level clouds centred on 32S/49.5E at 09Z. The associated convection has almost disappeared over the center, and resists vertical wind shear only in lines of convergence far from the center in the eastern quadrant, marking the end of the development potential.

The ASCAT runs of 0515Z and 0630Z show that the max winds reach the near gale force 30kt far from the center from 50mn to 150mn from the center in the North quadrant.

The low pressure circulation is expected to shift east-southeast over the next few days before merging with a baroclinic cold front by Friday evening.

There is no risk of formation of a moderate tropical storm over the basin for the next 5 days.

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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819
AWIO20 FMEE 090753

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2021/06/09 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


No significant convective activity over the basin.

Development of a moderate tropical storm is not expected for the next 5 days.

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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746
AWIO20 FMEE 101030

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2021/06/10 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


No significant convective activity over the basin.

Development of a moderate tropical storm is not expected for the next 5 days.

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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700
AWIO20 FMEE 151053

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2020/10/15 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The convective activity is moderate to strong on the extreme east of the basin, mainly east to 70E, within the building near equatorial trough. Satellite animation seems to confirm the possible presence of a closed clockwise circulation within the broad low level trough. However, it remains difficult to clearly discern this structure on the latest satellite images and the few available microwave images. It could be located at 10Z around 5.5S 80.5E.

In relation with the passage of an equatorial Rossby wave, this circulation should persist or even slightly intensify while moving southwestward, drawn towards a flat low circulating at south. On this track, the system should indeed benefit from an increase in upper divergence and a significant decrease in shear under the equatorial ridge. Nevertheless, environmental conditions do not permit this low to reach the moderate tropical storm stage. The convergence on the equatorial side will remain very weak, e
specially from Friday, when the circulation will be too far from the equatorial westerly. The deep shear is also expected to increase significantly from this weekend onwards as the upper trough in the southwest quadrant approaches. This scenario is well in agreement with the main deterministics.A few more Members than yesterday of the ensemble forecast propose winds close to gale force winds, but their number does not yet appear significant at the moment.

Development of a moderate tropical storm is not expected for the next 5 days.

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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300
AWIO20 FMEE 021140

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2020/10/02 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin retains its winter configuration with trade winds that reach up to the equator. However, two areas of deep convection have been in place for a few days in the near equatorial zone: one appeared towards the Seychelles and has shifted eastward today between the Chagos and the Seychelles and the other is located on the extreme North-East of our basin. The filtering of wind anomalies at 850 hPa shows that associated with these thunderstorm areas, there is a signature of Kelvin waves (for the westernmo
st pole) and the Equatorial Rossby wave (for the easternmost pole).

Over the next 2 days, these two equatorial waves will cross over the eastern half of our basin and may participate in the formation of a low-level clockwise circulation even in the absence of a well-defined Near Equatorial Trough (NET) pattern. However, in an environment not really conducive for cyclogenesis (little or no convergence on the equatorial side, persistence of a moderate to strong vertical easterly windshear), there is only a very small risk that this initial disturbance could intensify into a t
ropical storm. There is currently no significant signal on the deterministic models, and the EPS and GEFS ensembles suggest a weak signal between Monday and Wednesday somewhere south of the Chagos Archipelago, whereas this minimum should generally move westward.

For the next 5 days, the risk of formation of a moderate tropical storm becomes very low from Monday over the central part of the basin.

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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562
AWIO20 FMEE 031153

TROPICAL CYCLONE CENTER / RSMC LA REUNION / METEO-FRANCE

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

DATE: 2020/10/03 AT 1200 UTC

PART 1:

WARNING SUMMARY:


Nil.

PART 2 :
TROPICAL WEATHER DISCUSSION:


The basin is still showing a winter pattern with trade winds reaching the equator. However, deep convection has been present for a few days in the near equatorial area in the extreme northeastern part of our basin. Related to equatorial waves activity, in particular an Equatorial Rossby wave (analysis based on wind anomalies at 850hPa), a circulation could be form in the eastern part of the basin within a building Near Equatorial Trough.

However, the environment remains globally unfavorable to cyclogenesis: little or no convergence on the equatorial side, persistence of a moderate to strong easterly vertical shear. At long range, these conditions could improve slightly with a decrease of the constraint and a better feeding inflow on the equatorial side. Chances for development of a storm cannot be totally excluded then.

For the next 5 days, the risk of formation of a moderate tropical storm becomes very low on Wednesday over the central part of the basin.

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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