The deep depression over Bay of Bengal intensified into a cyclone on Sunday evening and is very likely to gather further strength becoming a severe cyclonic storm before crossing the Bangladesh coast on October 25 morning, the IMD said.

The cyclone, named Sitrang by Thailand, is very likely to intensify into a severe cyclonic storm on Monday with wind speed reaching 90 to 100 kmph gusting to 110 kmph, the India Meteorological Department (IMD) said.

It is likely to cause heavy to very heavy rain in the coastal districts of West Bengal and isolated heavy rain in north coastal Odisha, it said.

At 5.30 pm on Sunday, the cyclone was 580 km south of Sagar Island in West Bengal and 740 km south-southwest of Barisal in Bangladesh, it said.

It will mainly affect the Sunderbans spread over West Bengal and Bangladesh as tidal waves are likely to reach a height of six metres owing to the twin effect of the weather system and new moon, deputy director-general of the Regional Met Centre in Calcutta Sanjib Bandopadhyay said.

After changing course in a northeastward direction from northwest-bound, the system will reach north Bay of Bengal before making landfall between Tinkona island and Sandwip close to Barisal in Bangladesh in the early morning of Tuesday, he said.

Bandopadhyay said that light to moderate rain will occur in southern West Bengal districts till Wednesday morning owing to the system.

The system is very likely to bring heavy to very heavy rain in the coastal districts of South 24 Parganas and North 24 Parganas and heavy rain in East and West Midnapore on Monday, he said.

Calcutta, Howrah and Hooghly are likely to receive moderate rain on Monday and Tuesday, he said.

Heavy rain will occur in North and South 24 Parganas and Nadia districts on Tuesday, he said.

Sitrang will bring in its wake wind reaching speed of 80 to 90 kmph gusting to 100 kmph in coastal North and South 24 Parganas on Tuesday, while it will cause wind reaching speed of 45 to 55 kmph gusting to 65 kmph on Monday in these districts along with East Midnapore.

Calcutta, Howrah, Hooghly and West Midnapore are likely to be affected by wind reaching speed of 40 to 50 kmph gusting to 60 kmph on Tuesday, while it will be 30 to 40 kmph gusting to 50 kmph on Monday in these districts, Bandopadhyay told reporters.

"The main affected area will be the Sunderbans in the coastal areas of North and South 24 Parganas districts of West Bengal and in Bangladesh," he said.

He said that heavy rain, accompanied by wind gusting up to 100 kmph and high tidal waves is likely to cause damage to kutcha embankments and roads, disruption of power and communication lines and damage to kutcha houses.

Bandopadhyay said the major concern is that breakage of kutcha embankments owing to storm surge accompanied by the high astronomical tide on the new moon may lead to seawater inundation of low-lying areas in these places.

"The height of the waves due to the cyclone will be one metre above astronomical tide level, but since new moon is on October 25, the tide level owing to it will be five to six metres at West Bengal and Bangladesh coasts, so effective height of the tide at the time of landfall on the morning of that day will be around six metres in North and South 24 Parganas," he said.

South 24 Parganas' district magistrate Sumit Gupta said that already 10,000 people in the district have been moved to safer places, and work is on to shift another 30,000 people.

Seven teams of NDRF and SDRF with 26 personnel in each team were on standby in the district, he said.

The administration is also ensuring the safety of domestic animals, Gupta said.

The tide level is likely to be higher on the Bangladesh coast as the height of waves owing to the cyclone will be around two metres there.

The impending cyclone has dampened spirits of the people, from children to elders, planning to celebrate Kali Puja and Deepawali in a grand manner after a two-year pandemic-caused lull.

A Kolkata Municipal Corporation official said it has initiated steps to tackle any situation that may emerge owing to Sitrang in the metropolis, including keeping all pumping stations fully active and making arrangements for shifting residents of dilapidated buildings to schools and community halls.

The weather office warned that wind speed over sea areas will reach speed of 90 to 100 kmph gusting to 110 kmph in north Bay of Bengal, advising fishermen not to venture into the sea and the suspension of all offshore activities on October 24 and 25.

The weather office has advised suspension of ferry services in Sunderbans and water-bound tourist activities at the seaside resort towns of Digha, Mandarmoni, Shankarpur, Bakkhali and Sagar on October 24 and 25.

In Odisha, heavy rains are likely to lash certain places in the coastal districts of Kendrapara, Jagatsinghpur and Puri till 8.30 am on Monday.

A yellow warning of heavy rainfall was issued for Balasore, Bhadrak, Jajpur, Kendrapada, Jagatsinghpur, and Cuttack till Tuesday morning.

The Ganjam district administration has restricted entry of tourists to the Gopalpur beach.

"The restriction was imposed as people in large numbers thronged the beach on Sunday evening despite a cyclone warning," said a senior official.

The IMD also advised hoisting of Local Cautionary Signal Number Three (LC-III) at all ports of Odisha, denoting squally weather for ships.