Unusual January system brews over Bay of Bengal; heavy rain likely across parts of T.N.

In a rare January weather event, a system over the Bay of Bengal is likely to consolidate into a deep depression by Thursday (January 8, 2026) and trigger heavy rainfall in parts of Tamil Nadu. The Bay of Bengal has witnessed only 20 intense weather systems in January since 1891.

Rains are expected to pick up pace in coastal Tamil Nadu from Thursday, with widespread heavy rainfall across various coastal and adjoining districts till January 11.

B. Amudha, Head, (Additional in-charge), RMC, said it is unusual for such intense weather systems to form over the Bay of Bengal in January. However, there have been a few past instances when the Bay churned out intense weather systems that reached depression intensity or higher up to severe cyclonic storms during January, according to IMD’s Cyclone e-Atlas data from1891 to 2024.

The IMD is monitoring the possibility of the prevailing system gaining strength into a cyclone, she said.

Meteorologists pointed out that nearly 11 weather systems of depression intensity or higher have formed over the Bay of Bengal since 1961. Y.E.A. Raj, former deputy director general of meteorology, Chennai, said five of the January systems occurred between 2001 and 2024.

In January, the weather systems generally do not intensify much as conditions are often unfavourable. Such systems often tend to form at lower latitudes, and most of them dissipate over the ocean without making landfall, he said.

The increased detection of weather systems due to advances in observational tools was one of the reasons for rise in frequency of January systems during recent decades. Accurate and consistent records have been available since early 1960s, following the launch of satellite-based cyclone tracking. Data was obtained from conventional sources prior to that, he said.

Climate change may also be influencing recent changes in weather trends. But reasons behind such increase in intense weather systems need further study, said Mr. Raj.

The Regional Meteorological Centre forecast that the depression over southeast Bay of Bengal and adjoining East Equatorial Indian Ocean is likely to intensify into a deep depression by Thursday. It is likely to move west-northwestwards towards southwest Bay of Bengal during the subsequent 48 hours.

Five districts, including Ramanathapuram and Thanjavur, are likely to get heavy rainfall on Thursday. An orange alert has been issued to Thiruvarur and Nagapattinam as heavy to very heavy rainfall is possible on Friday (January 9, 2026). Intense downpour may continue in some delta districts on January 10. Northern districts, including Kallakurichi and Chennai, may come under the influence of heavy rainfall on Saturday (January 10, 2026) and Sunday (January 11, 2026).