The cyclone brewing on the Bay will have more impact in Bengal after landfall in Andhra Pradesh than when it is on the sea, said Met officials.

The system, around 1,200km away from the Bengal coast on Sunday morning, is expected to make landfall as a severe cyclonic storm near Kakinada, a port city in Andhra, on Tuesday night. After landfall, the storm is likely to move north.

"The northward movement may take the system, though depleted, towards Bihar. As it moves inland, the system is expected to inject sufficient moisture into Bengal. As a result, south Bengal is likely to get a rainy spell from Tuesday to Friday. Heavy rain is likely in some districts. In north Bengal, heavy rain is likely on October 30 and 31," said a Met official in Calcutta.

Calcutta is likely to get "thunderstorms" between Tuesday and Thursday, according to the Met forecast. Neighbouring South and North 24-Parganas are likely to get heavy rain, and some pockets, especially those neighbouring the two districts, may end up getting formidable rain.

The city sky turned cloudy on Sunday afternoon and some pockets got a drizzle or two. A Met official said it was because of local convection of clouds, aided by moisture and sufficient heating.

The deep depression was over the south-east Bay of Bengal around 8.30am on Sunday, said a Met bulletin. It was 620km from Port Blair (Andaman), 830km from Visakhapatnam (Andhra Pradesh) and 930km from Gopalpur (Odisha).

"It is likely to move nearly west-northwestwards, intensify further into a cyclonic storm over the southwest and adjoining west-central Bay of Bengal during the next 24 hours. Thereafter it is likely to move northwestwards, then north-northwestwards and intensify into a severe cyclonic storm by the morning of October 28 (Tuesday)," said the Met bulletin.

At its peak intensity, the storm will unleash winds consistently clocking upwards of 100kmph, with a peak wind speed of up to 110kmp, said the Met bulletin.

"Continuing to move further north-northwestwards, it is very likely to cross Andhra Pradesh coast between Machilipatnam and Kalingapatnam around Kakinada during the evening/night of October 28 as a severe cyclonic storm with a maximum sustained wind speed of 90-100kmph gusting up to 110kmph," the bulletin said.

Between Tuesday and Friday, heavy rain is likely in North and South 24-Parganas, East and West Midnapore, Jhargram, Howrah, Purulia, East and West Burdwan, Birbhum and Murshidabad.

Thunderstorms with gusts clocking 30 to 40kmph are expected in the rest of south Bengal.

In north Bengal, heavy rain is likely in Malda, North and South Dinajpur, Jalpaiguri, Kalimpong, Darjeeling and Alipurduar between October 30 and 31.