The weather department has sounded a cyclone warning for north Tamil Nadu and south coastal Andhra Pradesh.
The build-up has been spotted at an area in the Bay of Bengal about 90 km east of Chennai, said officials and the system will intensify into a cyclone in 24 to 48 hours. The wind speed is expected to reach 75 km per hour. Very heavy rainfall is expected in Chennai and parts of Tamil Nadu and also in Puducherry.
Fishermen have been warned against going to the sea. The depression in the Bay of Bengal has caused heavy rain in Chennai in peak summer.