Cyclone Remal intensified into a severe cyclonic storm on Sunday morning when it was raging on the north Bay of Bengal.

It remained so till Monday morning, hours after it had made landfall in the Sunderbans in Bangladesh.

The landfall process started around 8.30pm on Sunday, when the "forward sector of the wall cloud" started entering land. Much of the system was still on the Bay, 110km south-southeast of Canning and 130km south-southwest of Mongla, in Bangladesh. The core of the storm was 30km from the coastline.

The core or the centre of the storm entered land between 10.30pm on Sunday and 12.30am on Monday, the Met office said. Remal was then unleashing winds that consistently clocked between 110 and 120kmph, with gusts reaching up to 135kmph.

By 3.30am, it was still a severe cyclonic storm but the intensity had dropped marginally. Positioned around 130km east-southeast of Sagar Island and 60km southwest of Mongla, it was generating windspeeds of 90 to 100kmph, with gusts clocking 110kmph.

Once a cyclone makes landfall, it faces friction in the form of trees, buildings and poles. The result is a gradual dip in intensity.

By 5.30am, Remal had weakened into a cyclone and was around 150km northeast of Sagar Island, 70km northeast of Canning and 30km west-southwest of Mongla. The peak wind speed then was around 80-90kmph, with gusts clocking 100kmph.

Remal was 90km east of Calcutta around 8.30am on Monday, the closest it was to the city. But a dip in strength meant that the effect was not as much as it was a few hours ago.

By 2.30pm on Monday, the cyclone moved further north, positioned around 80km north-northwest of Mongla, 110km north-northeast of Canning and 120km east-northeast of Calcutta.

The peak wind speed had by then reduced to 80kmph.

A Met bulletin on Monday evening said around 5.30pm, Remal was 120km north of Mongla and 190km east-northeast of Calcutta.

"The system is likely to move nearly northeastwards, and gradually weaken further into a deep depression," said an official.