India: Cyclone brewing in Bay of Bengal could bring very heavy rainfall in Chennai

A prevailing low-pressure area over the south Andaman Sea and adjoining Southeast Bay of Bengal has evolved into a well-marked low pressure area as on Wednesday (Nov 29). On Thursday, it is likely to move north-northwest and concentrate into a depression, the Regional Meteorological Centre (RMC) said.

Typically, a low pressure area is where the atmospheric pressure is lesser than the surrounding regions. Low pressure areas are often associated with cloudy skies, windy conditions, rains and storms. 

The RMC, which comes under the Indian Meteorological Department (IMD), said that this evolving weather system is likely to intensify into a cyclone around the weekend.

In November, the northeast monsoon has been active over the Tamil Nadu coast and yielding good rains. Owing to the impact of the weather system, heavy rain has been forecast for Chennai city and adjoining districts, and other locations across coastal Tamil Nadu for Thursday and Friday.

Given that the cyclone is expected to form around the weekend, heavy to very heavy rainfall has been forecast for Chennai and adjoining districts for Saturday and Sunday.

The impact of this weather system could also bring heavy rains to other coastal districts of Tamil Nadu. As per the forecast, the heavy to very heavy rainfall could continue on Monday as well.

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In 2023, Chennai city and adjoining districts received considerable rainfall even during the non-monsoon months. This region usually gets the maximum share of rainfall during the October-December Northeast monsoon.  Of the reservoirs that supply water to Chennai, three are past 85 per cent storage capacity.

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As on Thursday, the Puzhal reservoir is at 86.73 per cent storage level, Thervoy Kandigai reservoir is at 90.40 per cent and Chembarambakkam reservoir is at 88.07 per cent, based on data from the Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB).

The Chembarambakkam reservoir outlet feeds into the Adyar river that meanders through Chennai and authorities have started gradually releasing water from the reservoir, as a measure of abundant precaution.

On Thursday, water from the Chembarambakkam reservoir is being let out into the Adyar river at a rate of 1,000 cusecs (1,000 cubic feet per second).