Well-marked low pressure area forms over Bay of Bengal, to trigger intense rainfall in Tamil Nadu

A well-marked low pressure area formed over the southwest Bay of Bengal on Tuesday (October 21, 2025). It is likely to trigger widespread, intense downpours particularly along coastal Tamil Nadu this week as it gathers strength.

The Regional Meteorological Centre (RMC), Chennai has sounded orange and yellow alerts for various parts of the State for the next four days, as weather systems over the Bay of Bengal and the Arabian sea continue to feed moisture into the region.

Orange alert

In its bulletin, the RMC has issued orange alert for seven coastal and delta districts, including Ramanathapuram, Cuddalore and Thanjavur and Puducherry, till 8.30 a.m. on Wednesday (October 22).

Chennai and its surrounding districts are among the 11 other districts expected to receive heavy rainfall during the 24 hours ending 8.30 a.m. on Wednesday. Tamil Nadu may experience such intense rainfall till October 24 depending on the movement of the weather systems.

Depression likely

According to the RMC, the well-marked low pressure area over southwest Bay of Bengal on Tuesday is likely to move west-northwestwards and consolidate into a depression over southwest and adjoining west-central Bay of Bengal off north Tamil Nadu and south Andhra Pradesh by Wednesday afternoon. It is likely to continue to move towards north Tamil Nadu, Puducherry and south Andhra Pradesh coasts and intensify further by Thursday.

Moreover, the low pressure area over southeast Arabian sea is likely to intensify into a depression by Wednesday.

Highest rainfall recorded

The vigorous monsoon battered several parts of Tamil Nadu with heavy to very heavy rainfall. During the past 24 hours ending 8.30 a.m. on Tuesday, Thangachimadam in Ramanathapuram district recorded the highest rainfall of 17 cm in Tamil Nadu.

Torrential rain pounded several places, including Pamban (15 cm), Mandapam (14 cm) in Ramanathapuram district and Varattupallam in Erode district (13 cm). Some places in Chennai like Medavakkam (10 cm) and Sholinganallur (8 cm) also recorded heavy rainfall. Many parts of the State continued to experience intermittent spells of rain on Tuesday, with short breaks of sunshine in between.

In its nowcast, the RMC has predicted moderate rainfall with thunderstorms in 14 districts, including Chennai, Cuddalore, Ariyalur, Nagapattinam and Ranipet and light rainfall in 19 other districts, including Theni and Salem, till 1 p.m.

Water discharge

Meanwhile, the Water Resources Department has increased water discharge from Red Hills reservoir, one of Chennai’s major drinking water sources, from 300 cubic feet per second (cusecs) to 500 cusecs at 9 a.m. today (October 21), following a marginal rise in inflow.