The Hindu Business Line : Eastern Bay warming up in advance of ‘low’

Thiruvananthapuram, April 2 The trough in the southeast Bay of Bengal has become less marked after northwesterlies made deep inroads into the region, but all the same leaving some headroom for the much-awaited ‘pre-monsoon low’ to evolve.

On Wednesday, the southwest, central and southeast Bay of Bengal had warmed up to some extent recording sea surface temperatures (SSTs) ranging from 28 deg C to 30 deg C. A still warmer spot showed up to the east of the Andaman Islands at around 32 deg C.

Warmer seawaters beyond a threshold 27.5 deg C aid convection to trigger formation of ‘low’s. Normally, the month of April sees two such systems evolve, which, at times, have gone on to become even cyclones.

EVEN CYCLONES

These cyclones generally move northward skirting the peninsular coast, choosing to hit the Orissa or West Bengal coasts, if not further east-northeast. One such cyclone during April 1991, ravaged the Bangladesh coast and killed 1.29 lakh people in one of the worst-ever disasters in the Bay of Bengal basin.

It all depends on where the low actually forms and how it sets up the needed moisture feed. On an average, the Bay sees at least six tropical cyclones take shape on either side of the monsoon mean. Two of them spring up in the pre-monsoon season while the rest get rustled up during the latter period of the monsoon and after it.

Last year, the pre-monsoon low had popped up in the southwest Bay, around Kanyakumari, on April 9, while the year before saw it getting delayed by more than a week (April 19, southeast Bay).

HEATING IMPEDED

But a major weather parameter helping pre-monsoon features to establish is the crucial April-time heating of the plains of north and central India as well as the peninsular north. Currently, the process has been corrupted by a prevailing western disturbance and the one that is expected to follow close on its heels.

Combined with induced cyclonic circulations, these drive down the mercury by a few notches in the north and northwest. According to the latest predictions, the thundershowers-to-thunder squalls activity in the region would hold until April 8 when the causative sub-tropical jet lifts itself away to the north of the land mass. The heating of the landmass is expected to resume after this.

RUNNING TROUGH

India Meteorological Department on Wednesday said that a cyclonic circulation thrown up by a line of converging winds lay over east Uttar Pradesh. A trough originating from this system ran down south to south Tamil Nadu through east Madhya Pradesh, Vidarbha Telangana and Rayalaseema.

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