Chennai and Puducherry on alert for intense weekend rain as Bay of Bengal system deepens

Chennai rain

Tamil Nadu is preparing for a spell of intense rainfall towards the weekend, as a well-marked low-pressure system over the southwest Bay of Bengal continues to strengthen and track towards the state’s northern coast, according to updates issued by the India Meteorological Department (IMD) and the Regional Meteorological Centre (RMC), Chennai.

The IMD said on Wednesday that the depression over the southwest Bay of Bengal, southeast Sri Lanka and the equatorial Indian Ocean is very likely to intensify further and continue to move north-northwestwards across southwest Bay of Bengal & adjoining Sri Lanka coast towards North Tamil Nadu, Puducherry and adjoining south Andhra Pradesh coast during the subsequent 48 hours.

The weather agency confirmed the formation of a low-pressure area under the broader influence of Cyclone Senyar, which is active farther east over the Strait of Malacca, near northeast Indonesia.

While Cyclone Senyar itself is not expected to directly affect Tamil Nadu, the IMD reiterated that heavy to very heavy rainfall is likely over the Andaman & Nicobar Islands on November 26–27 and heavy rain on November 28–29. The agency has maintained a rain warning for Chennai and several districts across the State as the Bay of Bengal system gains strength.

The RMC said the evolving system is likely to deepen into a depression by Thursday before progressing towards the Tamil Nadu–Puducherry stretch by Saturday. Its trajectory and potential intensification are being closely monitored, with senior officials signalling the possibility of further changes in the forecast.

B. Amudha, Head (Additional in-charge) of the RMC, said the current synoptic pattern suggests the system “can strengthen up to the stage of deep depression,” adding that rainfall alerts may be revised depending on shifts in the system’s movement and intensity in the coming days.

With the system poised to intensify, yellow alerts have been issued for five south coastal and delta districts, including Ramanathapuram and Thanjavur, for Thursday. For Friday, a mix of orange and yellow alerts has been sounded for Ariyalur, Cuddalore and adjoining districts, indicating the likelihood of heavy to very heavy rainfall.

By Saturday, rainfall is expected to spread across a wider geography, with north Tamil Nadu projected to receive intense showers of up to 21 cm on Saturday and Sunday. Chennai, Chengalpattu, Kancheepuram and Perambalur — all of which have registered rain deficits this month — are among the districts that could benefit from the anticipated wet spell.

A few locations in Chennai and surrounding districts may also experience heavy to very heavy rainfall over the weekend, with the RMC warning that conditions may evolve rapidly as the system approaches the coast.

Officials noted that despite a prolonged dry phase in many districts this month, Tamil Nadu’s overall Northeast Monsoon performance remains slightly above normal. The State has received 34.8 cm of rainfall since 1 October, four per cent higher than the seasonal average of 33.5 cm.

Even as Cyclone Senyar remains active over the Strait of Malacca, meteorologists underscored that the storm — currently positioned near the coastal areas of northeast Indonesia — is not expected to influence weather over Tamil Nadu. RMC officials emphasised that local rainfall will be driven entirely by the Bay of Bengal system, not by Senyar's circulation.

The coming days are expected to provide greater clarity on the evolving system’s strength, with the IMD likely to update its warnings as the weather disturbance moves closer to the Indian coastline. For now, authorities have urged residents in vulnerable districts to stay alert to forecast updates and district-level advisories.