A well-marked low-pressure area over southwest Bay of Bengal intensified into a depression on Thursday morning packing wind speed of 40-50 kmph as it moved towards the north Tamil Nadu coast, the weather office said.

It is expected to intensify further into a deep depression during the next 24 hours, the India Meteorological Department said.

The depression is likely to move west -northwestwards along and off the east coast of Sri Lanka towards north Tamil Nadu Coast during next 48 hours, it said.

At 5:30 am the depression lay centred over the southwest Bay of Bengal and adjoining the equatorial Indian Ocean about 470 km south-southeast of Trincomalee (Sri Lanka), 760 km south-southeast of Nagapattinam (Tamil Nadu) and 870 km south-southeast of Puducherry (Tamil Nadu) and about 950 km south-southeast of Chennai.

The IMD has warned of strong winds (45-55 km/hr gusting to an almost cyclonic 65 km/hr) over the south-west and adjoining west-central Bay of Bengal and along and off the Tamil Nadu-South Andhra Pradesh coasts and the Gulf of Mannar on Thursday.

On Friday and Saturday, squally weather (45-55 km/hr gusting to 65 km/hr) is likely over the West-Central and adjoining South-West Bay, and off North Tamil Nadu-Andhra Pradesh coasts.

On Sunday, wind speed may reduce slightly to 40-50 km/hr gusting to 60 km/hr over North Tamil Nadu-South Andhra Pradesh coasts.

The IMD has asked fishermen not to venture into South Bay of Bengal and adjoining Equatorial Indian Ocean, Gulf of Mannar and Comorin area till March 5; and southwest and adjoining areas of west-central Bay of Bengal and along Tamil Nadu, Puducherry and south Andhra Pradesh coasts on March 3 and March 5.

Isolated heavy rainfall is predicted in coastal Tamil Nadu, Puducherry and Karaikal on Thursday and Friday. Extremely heavy rainfall is very likely at isolated places in Tamil Nadu, Puducherry and Karaikal on Saturday, the Met department said.

The IMD added that sea conditions that had been rough over the South Bay of Bengal and adjoining Equatorial Indian Ocean, Gulf of Mannar and Comorin area since Wednesday morning is likely to become 'very rough' over southwest and adjoining the west-central Bay of Bengal during March 3 to March 5.