A rare weather event is underway over the Bay of Bengal. A system there is expected to become a deep depression by Thursday, January 8, 2026. This will lead to heavy rainfall in Tamil Nadu. Rainfall will increase along the coast from Thursday and continue through January 11 across coastal and nearby districts. B. Amudha, Head (Additional in-charge), Regional Meteorological Centre (RMC), noted this is unusual for January. Only 20 intense systems have formed in the Bay of Bengal during January since 1891, according to IMD's Cyclone e-Atlas data. The IMD is watching the storm closely. It may strengthen into a cyclone. Meteorologists said since 1961, about 11 weather systems of depression strength or higher have appeared in January. Y.E.A. Raj, former deputy director general of meteorology in Chennai, said five such systems occurred between 2001 and 2024. Raj explained January storms usually do not grow strong due to unfavourable conditions. Many start at lower latitudes and fade over the sea without hitting land. Better tools like satellites have increased detection of such systems in recent decades. Climate change might also affect weather trends, but more research is needed. The RMC forecast states the depression over the southeast Bay of Bengal and East Equatorial Indian Ocean will intensify and move west-northwest over 48 hours. On Thursday, Ramanathapuram and Thanjavur, among five districts, will see heavy rain. An orange alert is in force for Thiruvarur and Nagapattinam where heavy to very heavy rain could fall on Friday. Intense showers may continue in delta districts on January 10. Northern districts like Kallakurichi and Chennai might experience heavy rain on January 10 and 11.