Heavy rainfall drenches many parts of Tamil Nadu ahead of Northeast monsoon onset

Widespread rainfall lashed several parts of Tamil Nadu in the early hours of Wednesday (October 15, 2025), with a few coastal areas experiencing intense downpours, under the influence of a prevailing weather system over the Bay of Bengal.

Chennaiites woke up to intense rainfall on Wednesday as easterly winds strengthened over the region, signalling the impending arrival of the Northeast monsoon. The Regional Meteorological Centre on Tuesday (October 14) noted that the simultaneous withdrawal of the Southwest monsoon and onset of Northeast monsoon was likely by Thursday (October 16). A further update on the monsoon shift is awaited.

In the 24 hours ending 8.30 a.m., Ennore in Chennai recorded a very heavy rainfall of 14 cm. The bulk of rainfall in various parts of Tamil Nadu was received during the early morning hours of Wednesday. Kathivakkam (10 cm), Manali New Town in Chennai and Kodanad in Nilgiris district (9 cm each), Wimco Nagar in Chennai (8 cm), and Sembanarkoil in Mayiladuthurai (7 cm) also reported heavy rainfall.

Several other places, including Thiruvarur, Thanjavur, Vellore, Kallakurichi, Villupuram, Tirunelveli Pudukottai, Cuddalore, Thoothukudi, Ramanathapuram, Nagapattinam, Ranipet, and Tiruvallur, received light to moderate rainfall during the same period. Widespread showers had covered most of the coastal districts on Wednesday, marking a clear shift in weather patterns across the State.

An upper air cyclonic circulation over Southwest Bay of Bengal, which is likely to move towards the Comorin area, is cited to be one of the reasons for wet weather in the State.

RMC forecast

In its Nowcast valid till 1 p.m., the RMC has forecast light rainfall in isolated places over Tiruvallur, Chennai, Kancheepuram, Cuddalore, and Kallakurichi.

The RMC has predicted light to moderate rainfall to continue in many places. Heavy rain is likely to occur over the Ghat areas of Coimbatore, Nilgiris, Dindigul, Theni, Virudhunagar, Madurai, Sivaganga, Ramanathapuram, Thoothukudi, Tenkasi, Tirunelveli, and Kanyakumari districts on Wednesday.

Water release

Meanwhile, the Water Resources Department (WRD) plans to release about 700 cubic feet per second (cusecs) of water from the Poondi reservoir and 200 cusecs from the Red Hills reservoir at 2 p.m. on Wednesday.

Officials of the WRD said the water released into the Kosasthalaiyar river will reach the Tamaraipakkam anicut. From there, it would be diverted to Cholavaram tank for storage.

The shutters of the Poondi reservoir are being opened as it received heavy inflow of 2,260 cusecs from catchment areas, the Kesavaram anicut, the Illupur check dam, and the Kandaleru-Poondi canal.

According to the WRD’s compendium of rules, the reservoir water level must be maintained at 33 ft. in October. However, the water level now stands at 34.30 ft. and hence, measures are being taken to divert the excess to the Cholavaram tank for storage.

Officials said there are plans to release water from the Red Hills reservoir depending on the inflow and rainfall during the day. The reservoir, which is one of the major drinking water sources for Chennai, is filling up fast.

The Tiruvallur district administration has issued a flood warning to low-lying areas, including Vadakarai, Naravarikuppam, Sadayankuppam, and Kosapur, along the surplus course.