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Increasing uncertainty over enabling environment over the South Andaman Sea and the Bay of Bengal has ruled out any definite forecast with respect to the life of a resident low-pressure area, three days after its formation.

The India Meteorological Department (IMD) has merely decided to put the system under watch for the next seven days given the fact that the pre-monsoon season (April-May) can always throw up a surprise. It also referred to a series of projections by global weather models ranging from practically nil activity in the short to medium term over the Bay to a potentially strong cyclone developing there.

Restraining factors

What seem to prevent the intensification is the inconsistent cloud-building process around the system as well as a slight increase in the vertical wind shear (sudden change in wind speed and direction with height).

A storm can develop only in an environment of low vertical wind shear values. The IMD’s best hope is that the system could become well-marked over the South-East Bay around May 7 while moving slowly to the North-West (towards Tamil Nadu-Andhra Pradesh coasts) and concentrate into a depression the following day.

Currently, some global and domestic weather models do not even capture the low-pressure area. These include the European Centre for Medium-Range Weather Forecasts (ECMRWF); the IMD-GFS (Global Forecast System); the NCEP-GFS (the US National Centres for Environmental Prediction-Global Forecast System); the GEFS (Global Ensemble Forecast System); the NEPS (Ensemble Prediction System of India’s National Centres for Medium Range Weather Forecasting, NCMRWF); and the NCUM, a global coupled model from NCMRWF.

Models vary

But the ECMRWF, IMD-GFS, and NCEP-GFS signal cyclogenesis (birth of a cyclone) over the South-West Bay of Bengal (closer to the Sri Lanka and Tamil Nadu coasts) by end of next week with rapid intensification and a movement to the North-North-West into the East-Central Bay up to the Andhra Pradesh coast.

There is, however, large variation with respect to the date of cyclogenesis.

The IMD’s Genesis Potential Parameter-based outlook indicates that the zone of cyclogenesis may move North-North-West towards the East-Central Bay (open Bay waters) during the next four days.

It is in view of these conflicting outlooks that the IMD has resolved to keep the area over the Andaman Sea and the South Bay of Bengal under continuous watch for the next seven days.

The intensification of the prevailing low-pressure area would be a gradual and prolonged process, it added.

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