Cyclone Remal is likely to hit the Bengal-Bangladesh coast around Sunday midnight and bring "extremely heavy rain" with winds clocking up to 130km an hour, the Met office said on Friday evening.

What was a speck over the southwest Bay of Bengal on Wednesday became a well-marked low pressure on Thursday and a depression on Friday. It will become a cyclone by Saturday morning and a "severe cyclonic storm" as it nears land on Sunday morning.

The Met office has forecast possible landfall between Sagar Island at the southernmost tip of Bengal and Khepupara in Bangladesh. The two places are 400km apart. The closer the landfall is to Sagar, roughly 100km from Calcutta, the stronger the likely impact on the city.

The latest map shared by the Met office shows how close Calcutta is to the path Remal is likely to take in its course towards the coast.

The two 24-Parganas are likely to bear the brunt of the storm. Calcutta and Howrah are next in line.

Extremely heavy rain is expected in South and North 24-Parganas on Sunday. In Met parlance, extremely heavy rain means 200mm or above.

In South 24-Parganas, the rain will be accompanied by winds blowing at 100kmph to 110 kmph, with gusts clocking 120kmph, the forecast says.

Winds at 90-100kmph, with gusts clocking 110kmph, are likely in North 24-Parganas.

Calcutta, Howrah, Nadia and East Midnapore are expected to get winds blowing at 80-90kmph, with gusts clocking 100kmph.

On Sunday and Monday, heavy to very heavy rain is likely in Calcutta, Howrah, Hooghly, Nadia and East Midnapore. That means up to 120mm.

Fishermen have been asked not to venture into the sea between Friday and Monday.

Around 11.30am on Friday, the system lay in the form of a depression over the central Bay of Bengal, around 660km from Sagar Island.

Four years ago, Cyclone Amphan had made landfall in Sagar, almost flattening the island and causing large-scale damage in Calcutta.

“If this storm stays on the projected path, Calcutta will be within 100km of the centre of the storm,” said H.R. Biswas, head of the weather section at the Regional Meteorological Centre, Calcutta.

A radius of 200km from the centre of a storm is considered the impact zone.

In a city where weaker winds have uprooted trees and even a brief spell of steady rainfall leads to waterlogging, Remal could cause widespread damage.

“The depression over central Bay of Bengal moved north-northeastwards with a speed of 16kmph... and lay centred at 11.30am over east-central Bay of Bengal, about 700km south-southwest of Khepupara (Bangladesh), about 660km south-southeast of Sagar Islands (West Bengal) and 710km south of Canning (West Bengal),” the bulletin said.

“It is very likely to continue to move north-northeastwards and intensify into a cyclonic storm over east-central Bay of Bengal by 25th May morning. Subsequently, it would move nearly northwards, intensify into a severe cyclonic storm by 25th night. Continuing to move nearly northwards, it is very likely to cross Bangladesh and adjoining West Bengal coasts between Sagar Island and Khepupara around 26th May midnight as a severe cyclonic storm.”

Remal is expected to gain its highest intensity around Sunday evening when, as a severe cyclonic storm, it unleashes winds that clock up to 130kmph while still over the sea.

Remal is a name given by Oman, and means sand in Arabic.