North-east monsoon ends with 3% deficit rainfall in Tamil Nadu

Chennai: For the first time in six years, the North-east monsoon (NEM), Tamil Nadu’s lifeline, ended with a 3 per cent deficit rainfall on December 31, 2025, despite Cyclone Ditwah dumping huge amounts of rainfall across the state.

While Chennai, which experienced above-normal NEM for five years, also recorded deficit rainfall this season, Tirunelveli in southern Tamil Nadu recorded a remarkable 95 per cent increase.

2026 began on a pleasant note for residents of Chennai and its neighbouring districts with rains due to a weak cyclonic circulation over the Equatorial waters.

Southern Tamil Nadu and Delta region might get moderate rains for the next few days, even as the night time temperature is likely to remain slightly warmer than the past couple of weeks due to cloudy skies and rains.

The actual rainfall recorded between October 1, 2025 and December 31, 2025 is 428.9 mm against the normal rainfall of 442.8 mm. “The departure is minus 3 percent,” the IMD said on Thursday with experts saying that this is the first time since 2018 that the NEM has ended on a negative note.

With this, 2025 has become the 10th year since the start of the millennium to see the NEM not end on a positive note. Tamil Nadu relies heavily on NEM for rainfall, receiving about 48 per cent of its annual rain, making it the primary rainy season.

The NEM took off to a blistering start in October around the time of Deepavali by dumping rains across the state but went on a break in November and made a comeback in December.

Independent weather blogger Pradeep John said 2025 has been an unusual year with an abnormally high number of dry days with November and December alone recorded nearly 40 such days, which is significantly above normal for the NEM.

“After Cyclone Ditwah, except for the initial 4–5 days of rainfall, the state largely slipped into a rain-hibernation phase during December. With high pressure dominating, cold and dry weather prevailed across the state. A major reason for this prolonged dry spell was the complete absence of the Madden Julian Oscillation (MJO) over the Indian Ocean,” John said.

Thanks to south west monsoon rains and a “great October”, most of the lakes in Tamil Nadu are brimming, he said, adding that southern districts like Tirunelveli, Tenkasi, and Virudhunagar got good rains this season.

Another weather blogger K Srikanth said December saw only 45.8 mm, the lowest since 2018 which saw just 21.6 mm during the month.

“Though overall 2025 may have been a good year for most districts of Tamil Nadu and Puducherry, the same cannot be said about NEM. For the year overall only 13 out of the 40 districts ended with negative anomaly. Chengalpattu saw the worst performance among all districts ending the year with a 20 per cent deficit while Dindigul, Karur and Tiruppur also saw nearly 20 per cent deficit,” he said.