CHENNAI: Even before the onset of the Northeast Monsoon (NEM), interior Tamil Nadu districts — among the least rainfed regions in the state — have already received over 40% of their seasonal rainfall. The India Meteorological Department (IMD) said the NEM is likely to set in around October 16, and the rainfall this season is expected to be above normal across South Peninsular India.
As per official data, Dharmapuri, which normally receives 314.2 mm of rainfall during monsoon, has already logged 125.8 mm between October 1 and 11. Krishnagiri and Tirupattur have received 121.7 mm and 113.8 mm, respectively, against their seasonal averages of 278.7 mm and 266.3 mm.
In the past 24 hours ending 8.30 pm on Saturday, Marandahalli in Dharmapuri recorded the TN’s highest rainfall of 18 cm. The forecast for the next five days shows heavy rain, due to upper air circulation, over ghat areas of Coimbatore, Tirunelveli, Nilgiris, Theni, Tenkasi, Madurai, Dindigul, Tiruchy, Salem and Namakkal.
The IMD’s long-range forecast indicates that rainfall averaged over South Peninsular India during the NEM is “most likely to be above normal” - over 112% of the long period average (LPA). The LPA for the post-monsoon season, based on 1971-2020 data, is 334.13 mm.
Recent trends show growing erratic rainfall behaviour in these regions. In 2024, Dharmapuri, Krishnagiri, and Tirupattur received excess rainfall of 60%-86%, while in 2023, they got only half their seasonal averages. In 2022, the same districts saw 16%-55% excess rain, underscoring NEM’s volatility in interior TN.
Weather bloggers K Srikanth and Pradeep John noted that October is a highly active month for thunderstorms, coinciding with the southwest monsoon withdrawal and NEM onset. “When the withdrawal is delayed, as is the case this year, the transition happens rapidly, leading to intense thunderstorms,” they said.
Climate scientist Madhavan Nair Rajeevan, V-C of Atrai University, said monsoons are becoming highly erratic due to global warming. “Localised extreme weather events like the recent cloudbursts in Chennai are expected to increase as elevated moisture levels fuel intense convective activity. Predicting such events remains a major challenge,” he noted.
Poornima Prabhakaran, director, Centre for Health Analytics Research and Trends, Ashoka University, said her team will be researching the monsoon and its impact on non-communicable diseases.