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Vinson Kurian

Thiruvananthapuram April 12 Contrary to forecasts, Wednesday's low-pressure area in the Gulf of Mannar veered away to the south-southwest beyond Sri Lanka on Thursday, bringing about appreciable decline in thunderstorm activity over extreme south Indian peninsula.

Only scattered rain/thundershowers have been indicated for the region over the next two to three days, according to a forecast by the National Centre for Medium Term Weather Forecasting (NCMRWF).

But North-East India will continue to witness heightened thunderstorm activity with the Nor'Westers expected to hold strong for 36-48 hours.

Nor'Westers are seasonal in nature and raid the North-Eastern States during pre-monsoon.

BAY WARMING UP

The prevailing `low' just passing Sri Lanka may have prepared the ground for more cyclonic circulations to form in the Bay of Bengal, some of which can descend to lower levels and become low-pressure areas themselves.

According to Mr J.V. Singh of the NCMRWF, the Bay of Bengal has warmed up suitably to play host to these weather systems.

While `in situ' (home-grown) systems may not be a frequent occurrence in the Bay during this time of the year, easterly waves with embedded troughs would find prevailing conditions congenial to get charged up and become `lows' or depressions.

They are known to take a westward or west-northwestward track and impact the country's south-eastern coast.

WIND DISCONTINUITY

The line of `wind discontinuity' that links north peninsular India with the south, a typical pre-monsoon feature and semi-permanent in nature, persists.

Drier north to north-westerly winds meet the moist south-easterlies along this `dent' in the atmosphere to set up thunderstorms.

An Ohio State University update said that the discontinuity extended from Vidarbha to south Tamil Nadu through Marathwada, Telengana and south interior Karnataka.

In the North-East, there is a trough in the lower level westerlies extending from Bihar to North Bay of Bengal.

This doubles up as the playground for Nor'Westers and associated thunderstorms that stalk the region.

The NCMRWF forecast said that isolated heavy falls are likely over Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura during the next 24 hours.

With the likely weakening and eastwards movement of the trough, the ongoing rainfall activity in the region is likely to decrease after Friday.

With the likely gradual rise in day temperatures, these conditions are likely to extend to some more parts of North-West and adjoining Central India during the next 3-4 days.

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Thunderstorms relent as `low' veers off to south

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