The rains started on Monday in coastal parts of northern Tamil Nadu continues till Wednesday.
IMD, in its bulletin today morning said that the depression over southwest Bay of Bengal moved nearly northwards in past six hours and lay centred at about 90 km east of Chennai and about 70 km from the coast.
"The system is likely to move north-northeastwards and intensify into a deep depression and further into a cyclonic storm in during next 48 hours," it said.
The department warned rainfall at most places with heavy to very heavy falls at a few places with isolated extremely heavy falls over north coastal Tamil Nadu and Puducherry during next 24 hours. Rainfall at many places with isolated heavy falls likely over south coastal and interior Tamil Nadu during the same period.
Squally wind speed reaching 55-65 kmph gusting to 75 kmph would prevail along and off north Tamil Nadu and Puducherry during next 24 hours and south Andhra Pradesh coasts during next 48 hours, it added.
Fishermen were advised not to venture into sea along and off Tamil Nadu & Puducherry and south Andhra Pradesh, Kerala coasts and Lakshadweep area during next 48 hours.