The Low Pressure Area in the south and the central Bay of Bengal is expected to get intensified into a Depression by today.
Met Department in Chennai said it will turn into a cyclone in the next 24-hours.
It is likely to make landfall on Wednesday between Karaikal in Puducherry and Mamallapuram in northern Tamil Nadu.
As per the naming convention, the cyclone in the Bay of Bengal will be known by the name Nivar, once it is formed.
Weather officials say Nagapattinam, Thanjavur and Tiruvarur will experience isolated heavy rain today.
They say, very heavy rain will be recorded tomorrow in seven districts in the delta region and
central Tamil Nadu and Karaikal.
12 other districts including Chennai and Puducherry are expected to witness isolated heavy rain.
On Wednesday, the day of the landfall, 27 of the 37 districts in Tamil Nadu and Karaikal and Puducherry falling under the neighbouring
Union Territory will get heavy to very heavy rain.
Fishermen have been asked not to venture into the sea during the period, due to rough weather.
Currently, barring four districts in Tamil Nadu, all others are deficient in rainfall.
The shortfall is expected to be offset by the rain during the cyclone.