India Meteorological Department (IMD) has assessed that a low-pressure area, the first of the North-East monsoon season, is likely to form over the South-West Bay of Bengal off the Sri Lanka coast on Wednesday next (November 9), which is expected to move West-North-West towards the Tamil Nadu-Puducherry coast with slight intensification in the subsequent two days. 

This would scale up the rainfall during the period under reference even as IMD’s numerical models, on Friday, suggested that the easterly wave with a rain-head upfront is already active over the South Bay. The ‘low’ will pop up from the easterly wave extending from Sumatra and head towards Sri Lanka before breaking away to move towards the Tamil Nadu coast. 

May cross Chennai coast

Early forecasts suggested that the system may cross the Chennai coast by November 11 accompanied by a flurry of rainfall activity ahead and after the event. The IMD said the easterly wave activity combined with the low-pressure system will trigger light to moderate to scattered to fairly widespread rainfall over most parts of the South Peninsula during the November 10-16. Isolated heavy to very heavy rainfall is also likely over Tamil Nadu and Kerala during many days of the week.

Overall rainfall activity is likely to be normal to above-normal over Tamil Nadu, Puducherry, and Karaikal; Kerala and Mahe; South Interior, North Interior, and Coastal Karnataka; Rayalaseema and South Coastal Andhra Pradesh; near-normal over East and North-East India; and below-normal over North-West and Central India as western disturbances apparently take a break, the IMD said. 

Circulation, trough stay May 

On Friday morning, a cyclonic circulation lay over Kerala from which an East-West trough extended to the South Andaman Sea across South Tamil Nadu. Another cyclonic circulation was parked over the South Andaman Sea and adjoining South-East Bay, shepherding the north-easterly flows. Fairly widespread to widespread light to moderate rainfall with isolated heavy falls, thunderstorms, and lightning will continue to hit Tamil Nadu, Puducherry, Karaikal, Kerala, and Mahe until Tuesday. Early next week, the low-pressure system will bring heavy rainfall along the coast and the interior South Peninsula.  

Weak during November 11-19 

An outlook for November 9-11 said fairly widespread to widespread light to moderate rainfall will lash parts of the South Peninsula and the Islands with isolated heavy falls over Tamil Nadu and Kerala. The US National Centres for Environmental Prediction says rainfall may lose some intensity during November 11-19 but say above-normal over North Coastal Tamil Nadu, including Chennai; Coastal Andhra Pradesh; and Central and North Kerala.

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