Low Pressure Area Over Bay Of Bengal: Heavy Rains Over Tamil Nadu Likely

Key Takeaways:

• A low-pressure area over the Southwest Bay of Bengal is expected to intensify northeast monsoon activity across Tamil Nadu.
• Chennai is likely to receive heavy rainfall for the next three days, while coastal areas may experience heavy to very heavy showers during the next 48 hours.
• Chennai's Meenambakkam and Nungambakkam observatories have recorded 321.3 mm and 349.2 mm of rainfall, respectively, between 1 and 21 October, exceeding the monthly normal of 300.3 mm.
• Forecast Validity: 21–28 October 2026 (next seven days) — Heavy rainfall is expected until 25 October, with lighter showers on 26–27 October and improvement likely after 27 October.

Under the influence of a cyclonic circulation over the Southwest Bay of Bengal (BoB), a low-pressure area has formed over the same region, off the Tamil Nadu coast. Northeast monsoon activity will pick up over the South Peninsula in general and the state of Tamil Nadu in particular. In the state, heavy rainfall is expected for the capital city, Chennai, for the next three days.

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The low-pressure area over the Southwest BoB is likely to stay close to the coast for about the next 72 hours. A north-south trough is extending up to 10,000 feet from the centre of circulation to North Coastal Andhra Pradesh, running nearly parallel to the coast. A strong northeasterly stream from the central parts of the BoB is converging onto the coastline of Tamil Nadu. Under the combined influence of these features, active to vigorous monsoon activity is likely for about the next seven days, covering all parts of the state.

The capital city, Chennai, witnessed heavy rainfall for the second time after the onset of the northeast monsoon on 15 October 2026. The airport observatory at Meenambakkam and the regional observatory at Nungambakkam recorded 129 mm and 112 mm of rainfall, respectively. Earlier, both these stations had registered rainfall in excess of 100 mm each on 18 October 2026. With this heavy spell, both locations have crossed the monthly normal figure of 300.3 mm. The airport has measured 321.3 mm, and the regional station has accumulated 349.2 mm of rainfall between 1 and 21 October 2026. More showers will follow, and the city may record its all-time highest monthly rainfall, overtaking the earlier figure of 422.4 mm established in October 2012.

The entire coastline is expected to be lashed by heavy rainfall, with very heavy rainfall at isolated places, in the next 48 hours. Thereafter, the intense weather activity will shift to the interiors of the state for the subsequent three days, until 25 October. Rainfall will become light and scattered between 26 and 27 October. The possibility of a storm forming over the BoB around 27 October will reduce the flow of moist winds along the coastline. Broad improvement in weather conditions is likely after 27 October. The forecast will be subject to revision, and an update will be shared by the weekend.