As cyclone Amphan is closer to hit coastline of India and Bangladesh, both the countries have already evacuated almost a million people in safe areas.

Experts believe that cyclone Amphan is likely to weaken into an extremely severe cyclonic storm. It moves north-northeastwards over the Bay of Bengal and cross West Bengal-Bangladesh coasts between Digha and Hatia Islands during Wednesday afternoon.

Already downgraded to Category 4, Cyclone Amphan could weaken further by the time it makes landfall close to the western Sundarbans, experts said yesterday.

Indian and Bangladesh Meteorological office said it may hit the coastal areas of Bangladesh and India today evening.

The cyclone, under the influence of the new moon phase, could cause storm surges above 10 feet in coastal districts including Satkhira, Khulna, Bagerhat, Jhalakathi, Pirjojpur, Barguna, Patuakhali, Bhola, Barishal, Laxmipur, Chandpur, Noakhali, Feni and Chattogram.

Weather experts said Amphan turned into an extremely severe or category 4 cyclone from category 1 within just 18 hours as the temperature of the sea surface in the Bay had been very high (32 to 34 centigrade) over last two weeks.

"We have never seen such high values until now. These high temperatures can super charge a cyclone since tropical cyclones primarily draw their energy from evaporation at the ocean surface," Dr Roxy Mathew Koll, a scientist at the Indian Institute of Tropical Meteorology, wrote on his Facebook page yesterday.

"The evacuation of people in the coastal areas will continue the whole night. Many will move to cyclone shelters after Sehri. The number of evacuees will be nearly 20 lakh by tomorrow morning," said Enamur Rahman, state minister for disaster management and relief.

They, however, expressed concern that it might still wreak serious havoc on Bangladesh as a storm surge, depending on the tide.

Md Shah Alam, former director of Bangladesh Meteorological Department (BMD), said the wind speed of the cyclone would certainly be less at landfall than at the sea.

He said the storm surge would depend on when the cyclone makes landfall -- during high tide or low tide.

Another point of concern was that the cyclone still continued to cover a large swathe of the funnel-like Bay, pushing waters northwards, which would only worsen the storm surge around the time it hits, Shah Alam added.

Quamrul Hasan, the BMD forecast officer on duty, said the main feature of this cyclone is its speed, sea surface temperature and radius.

Experts said Amphan is only the second super cyclone formed over the Bay of Bengal after the 1999 Oddissa cyclone. This is the first super cyclone over the Bay in this century.

The Joint Typhoon Warning Centre said sustained wind speed of Amphan would be just below 160 km per hour at landfall, which would further weaken the cyclone to Category 3.

According to Indian Meteorological Department, 46 severe cyclonic storms were registered in the Bay of Bengal and the Arabian Sea from 1965 to 2017.

In terms of fatalities, Bangladesh was hit by seven of the worst cyclones recorded in history, with the Bhola Cyclone killing between 3 to 5 lakh people in 1970. The cyclone had brought a a 20-feet storm surge.

"The most serious threat posed by Amphan is its potentially catastrophic storm surge. Even if Amphan's top winds weaken, the storm surge threat will remain dire," said Weather Underground, a commercial weather forecast organisation.

Prof Mahbuba Nasreen, director of Dhaka University Institute of Disaster Management and Vulnerability Studies, said cyclone Amphan is different because of its nature.

As per the latest update issued by the India Meteorological Department (IMD), the ‘extremely severe’ cyclonic storm lay centred over northwest and adjoining westcentral Bay of Bengal, about 250 km south of Paradip in Odisha and 390 km south-southwest of Digha in West Bengal and 540 km south-southwest of Khepupara in Bangladesh.

Cyclone Amphan, Weather Forecast: Massive evacuation as Cyclone Amphan becomes a 'super cyclone'; NDRF deploys teams in Odisha, West Bengal. Read live updates, latest news in Bangla, Malayalm, Tamil, Hindi

West Bengal scrambled to evacuate around 3 lakh people from coastal and low-lying areas to shelters as Cyclone Amphan — moving at a speed of 18 km/hr — is expected to make landfall between West Bengal’s Digha and Hatiya islands in Bangladesh on Wednesday and push up the sea level.

Indian meteorological officials said Cyclone Amphan, which has now weakened from Super Cyclone to an Extremely Severe Cyclonic Storm, will have a wind speed ranging between 155–165 km/hr when it makes landfall on Wednesday.

With the report from Indian Express and Daily Star