India Meteorological Department (IMD) expects the ongoing heavy rainfall spells to continue over Tamil Nadu and Rayalaseema during the next five days as the numerical models employed by the national weather forecaster suggested that the North-East monsoon (NEM) may not set in for the next week to 10 days. But it is likely the season may set in during the normal window of October 18 to 22, with supporting weather systems brewing in the Bay of Bengal in time.

The 24 hours ending at 8 am on Tuesday saw the following stations receive heavy to very heavy rain with extremely heavy falls (in cm) in Tamil Nadu: Metupatti-17; Panchapatti-12; Thammampatty and Pulipatti-9 each; Tirupattur-8, and Vedipatti and Erode-7 each. In South Interior Karnataka, these are: Pavagada-10, Davanagere-9; and, YN Hoskote-7; North Interior Karnataka: Tavaragera -8 and Badami-7; and Coastal Andhra Pradesh: Peddapuram-7.

More heavy rain forecast

Fairly widespread to widespread light to moderate rainfall is likely over Tamil Nadu, Puducherry and Karaikal until Saturday; Rayalaseema until Thursday; North Interior Karnataka on Wednesday; South Interior Karnataka on Wednesday and Saturday; Coastal Andhra Pradesh and Yanam on Thursday and Friday; and Kerala and Mahe on Saturday.

Elsewhere, fairly widespread to widespread light to moderate rainfall with isolated heavy falls are likely over the hills of West Bengal, Sikkim and Bihar on Wednesday. It will be fairly widespread to widespread light to moderate rainfall with isolated heavy falls, thunderstorms, lightning over Arunachal Pradesh, Assam, Meghalaya and Nagaland, Manipur, Mizoram and Tripura on Wednesday. Parts of north-west and east India are also under cloud cover, which has not allowed the withdrawal of predecessor South-West monsoon to resume from north-west India.

Withdrawal stays stalled

A network of supporting trough and cyclonic circulations are holding up the withdrawal, which, the IMD said, may resume in the next three-four days (mid-October) as predicted earlier in these columns. The anticyclone that oversees the withdrawal has to evolve fully over north-west India before the NEM can prosper over the South Peninsula. This is because the north-easterlies and progressively easterlies along the southern flanks of the anticyclone add momentum to the NEM. This may not happen before October 20.

Bloggers on track

Meanwhile, weather bloggers in Tamil Nadu have been tracking the developments on the impending North-East monsoon in right earnest. @jhrishi2 tweeted, “good signs of #NEM2022 onset brewing with a traditional dumbbell shape pattern brewing around 3rd week which will eventually increase rainfall activity over coastal #TamilNadu in the coming days. Will be interesting to see if a system develops from this.”

Twitterati get busier

Not surprisingly, @chennai13621472 tweeted: “expected cyclonic circulation (may) form over South-West Bay of Bengal. Widespread rain possible for Tamil Nadu as it nears the coast (October 8-10). Seems #NEM2022 onset could be delayed to November first week.” @sel said: “After dumbbell- shaped pressure pattern establishment on either sides of South India by October 17, now inverted V-shaped trough seen around the leading edge of incoming easterlies, affecting East Coast by October 19. All these are indications of #NEM2022 arrival.”

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