Thunderstorms rule even as heavy rains lash peninsula

Heavy rain is forecast to continue over Tamil Nadu and parts of Kerala on Friday even as observations suggested that north-east India has slipped under the ‘ Kalbaisakhi ’ (seasonal thundershower) season.

Troughs (warmed surfaces creating areas of lower pressure and in turn thunderclouds) persisted over southwest Bay of Bengal (off Sri Lanka and Tamil Nadu) and South Andaman Sea.

Moisture feed Forecasts indicate that the first trough will stay put though its orientation (from east-west to north-south) may change in between.

It will continue to feed moist south-easterly winds into peninsular India.

To the north, a seasonal high-pressure area (representing hot and dry air mass) will push from the Arabian Gulf into Iran-Afghanistan-Pakistan and into north-west India.

Its push will be contained by a land-based trough over east and north-east India and dipping into east central India.

This is what will sustain the Kalbaisakhi season in north-east India and Bangladesh.

This is a major pre-monsoon event in the region, caused by nor’westers (north-westerly current blowing across the plains of north India), and is known for its destructive impact on life and property.

The north-westerly winds are the extension of a western disturbance lying over north Pakistan and adjoining Jammu and Kashmir.

Line of fire The high-pressure area over Gujarat and Rajasthan will spare them from resultant thundershowers, which will be confined to Himachal Pradesh, Punjab, Uttarakhand, Delhi, and west Uttar Pradesh.

This western disturbance has cut open a north-south trough from central Uttar Pradesh extending south right down to the Comorin region (Arabian Sea).

This is the ‘line of fire’ along which thunderstorms breed and responsible for the turbulent weather over the trunk of the country.

This is where incremental moisture is being piped in from the Bay of Bengal.

Heavy to very heavy rain has been recorded over Tamil Nadu and parts of Kerala overnight on Thursday, India Met Department said.

Periakulam in Tamil Nadu saw 15 cm of rain while Chennai and a number of other cities recorded 10 cm each.

In Kerala, the rains were concentrated to the central and northern parts of the state.

Weather warning Friday: Heavy rainfall at isolated places over interior Tamil Nadu and Kerala. Thunderstorms with squall/hail over Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura.

Saturday: Heavy to very rainfall for isolated places over Arunachal Pradesh, Assam, Meghalaya; heavy rainfall at isolated places over Nagaland, Manipur, Mizoram and Tripura. Thunderstorms with squall/hail along the hills of West Bengal, Sikkim, Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura.

Sunday: Heavy rain at isolated places over Arunachal Pradesh, Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura. Thunderstorms with squall/hail over the hills of West Bengal and Sikkim.

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