A “severe cyclonic storm” that is expected to hit the Odisha-Bengal coast later this week is taking shape over the Bay of Bengal.

The precursor to the system, a low-pressure area on the east-central Bay, has started gaining momentum.

Aided by a conducive sea-surface temperature and wind patterns, it is expected to intensify into a cyclone — Dana, named by Qatar — by October 23 and a severe cyclonic storm by the morning of October 24.

It is expected to hit land between Puri in Odisha and Sagar Island on the southernmost tip of Bengal — sustaining its intensity as a severe cyclonic storm — between the night of October 24 and the morning of October 25, according to the Met projection.

At the time of landfall, the system is expected to unleash winds blowing at 120kmph in and around the landfall point. Swathes of south Bengal, including Calcutta, are likely to be pounded by heavy rain on October 24 and 25, the Met office has warned.

“The low-pressure area over east-central Bay of Bengal and adjoining north Andaman Sea moved west-northwestwards and lay as a well-marked low-pressure area over east-central Bay of Bengal at 11.30am. It is very likely to move west-northwestwards and intensify into a depression by 22nd October morning and into a cyclonic storm by 23rd October over east-central Bay of Bengal,” said a Met bulletin issued on Monday afternoon.

“Thereafter, it is very likely to move northwest and reach northwest Bay of Bengal off Odisha-West Bengal coasts by 24th October morning. Continuing to move northwestwards, it is very likely to cross north Odisha and West Bengal coasts between Puri and Sagar Island between the night of 24th and early morning of 25th October as a severe cyclonic storm with a wind speed of 100-110kmph gusting 120kmph.”

The distance between Puri and Sagar Island is over 420km. A forecast track issued by the Met office on Monday shows north Odisha as the possible area of landfall but the accompanying cone of uncertainty almost reaches Sagar Island, near the Sunderbans.

As the storm comes near the coast, Met officials said they would be in a better position to narrow down the expected area of landfall and the cone of uncertainty will become narrower.

Remal was the last severe cyclonic storm that came Bengal’s way — in May this year. The storm made landfall, as a severe cyclonic storm, in the Sunderbans in Bangladesh on May 26 morning. The storm was around 25km from the tip of the Indian Sunderbans, approximately 140km from Calcutta. Winds clocking up to 91km an hour felled more than 400 trees in and around the city. There was more than 250mm of rain in 24 hours, flooding many areas.

Under Cyclone Dana’s influence, the coastal areas of Bengal and Odisha are
likely to get rain from October 23. The intensity of the showers will peak on October 24 and 25.

The Met bulletin gave day-specific warnings:

October 23: Heavy rainfall (7-11cm) in East and West Midnapore and North and South 24-Parganas districts. Light to moderate rain/thundershowers at many places in East and West Midnapore and North and South 24-Parganas and a few places in the remaining districts of south Bengal.

October 24: Extremely heavy rain (more than 20cm) in East Midnapore, West Midnapore and South 24-Parganas districts; heavy to very heavy rain (7-20cm) at one or two places in Calcutta, Howrah, Hooghly, North 24-Parganas and Jhargram districts; heavy rain in the remaining districts of south Bengal.

October 25: Extremely heavy rain in West Midnapore and Jhargram districts. Heavy to very heavy rain in East Midnapore, South 24-Parganas, North 24-Parganas, Calcutta, Howrah, Hooghly, Purulia and Bankura districts.