Satellite view of Cyclone Amphan on May 19, 2020. (Weathernerds.org)

Category 3 Tropical Cyclone Amphan is barreling northward toward the mouth of the Bay of Bengal on Tuesday and is forecast to make landfall in West Bengal, India, just south of Kolkata, on Wednesday. The storm is prompting officials in the states of Odisha and West Bengal, as well as in neighboring Bangladesh, to try to evacuate 3 million people out of harm’s way, given that this region is among the most vulnerable parts of the world to storm-surge flooding.

Both India and Bangladesh have made great strides in recent years with evacuations and bringing vulnerable residents to storm shelters, but this year those efforts are complicated by the coronavirus pandemic, which is making many residents fearful of going to confined spaces.

The storm had been a Category 5 monster on Monday, setting a record for the strongest such storm on record in that part of the world, but even nature’s most intense storms are surprisingly delicate. Strong winds carrying relatively dry air surrounding the storm have slipped into the core of Amphan (pronounced “UM-PHUN”), disrupting the inner ring of thunderstorms known as the eyewall, which contains the storm’s strongest winds and heaviest rains.

Since Monday night, the eyewall has been open on the eastern side, reflecting the influence of the wind shear and dry air. For the storm to intensify, the eyewall needs to be completely closed. On Tuesday evening, the Joint Typhoon Warning Center noted some signs that the weakening trend has abated, and forecasts call for the storm to maintain Category 2 intensity through landfall.

However, because Cyclone Amphan was once a “super cyclonic storm” at the pinnacle of storm intensity, it is pushing water toward shore that is more consistent with a much stronger storm.

This phenomenon of a weakened storm in terms of wind speeds bringing a storm surge commensurate with a more powerful weather system has played out in the United States. Hurricane Katrina, for example, struck the Gulf Coast in 2005 as a Category 3 storm, but its surge was more in line with a Category 5 storm, since it had previously achieved Category 5 status. The storm surge is the storm-driven rise in water above normally dry land.


Microwave satellite image of Cyclone Amphan's inner core, showing the exposed eyewall on the storm's eastern side. This is indicative of a weaker storm. (U-Wisconsin CIMSS) (U-Wisconsin/CIMSS)

Water is a tropical cyclone’s greatest killer, both from storm surge and inland flooding due to heavy rainfall. The Indian Meteorological Department, which is issuing warnings for Cyclone Amphan, is predicting a storm surge of about 13 to 16 feet (4 to 5 meters) above astronomical tide, which it says “is likely to inundate low-lying areas of south and north 24 Parganas and about 10 to 13 feet (3 to 4 meters) over the low-lying areas of East Medinipur District of West Bengal during the time of landfall.”

Areas along and to the right of the storm’s center at landfall will see the biggest surge, since the onshore winds will be maximized there.

The shape of the Bay of Bengal maximizes storm surge at its northern end, since the region becomes narrower as storms spin farther to the north, creating a funnel effect for the movement of water.

Past storms that have struck this densely populated region have killed tens of thousands of people and displaced thousands more. A 1999 cyclone that struck Odisha killed about 10,000 people in northeastern India. The deadliest storm on record globally was the 1970 Bhola Cyclone, which made landfall in Bangladesh and killed an estimated 300,000 to 500,000 people.

Like many powerful storms in recent years, Tropical Cyclone Amphan underwent a period of rapid intensification Sunday night, feasting upon the warm waters of the Bay of Bengal and the absence of wind shear that could have interfered with its circulation, as well as abundant moisture surrounding the storm.

Based on data from the typhoon warning center, Cyclone Amphan intensified by 110 mph in just 36 hours. “That would certainly put it in a rare class of [rapid intensification] events globally,” said meteorologist Alex Lamers via Twitter. It also jumped in intensity from a Category 1 storm to a Category 5 monster in just 24 hours, according to Bob Henson of Weather Underground.

Rapidly intensifying storms constitute one of the impacts that scientists have seen from human-caused global warming, with studies pointing increasingly to the dangers posed by storms that make a sudden leap in intensity categories.

Globally, the odds of the strongest tropical cyclones, such as Category 3, 4 and 5 storms, are increasing due to climate change, according to a study published Monday. However, that study did not find clear trends in the North Indian Ocean Basin.

Evacuation efforts collide with the coronavirus pandemic


This photograph provided by India's National Disaster Response Force shows personnel making announcements to warn people on the Bay of Bengal coast about Cyclone Amphan at Namkhana, South 24 Parganas, West Bengal, India on Tuesday. (National Disaster Response Force/AP)

The chief minister of West Bengal said that nearly 300,000 people have been evacuated. In Odisha, more than 60,000 have already been evacuated, but as many as 1.1 million may be shifted to shelters. In Bangladesh, the figure could reach 2 million, said Mohammad Mohsin, director general of country’s disaster management department.

Among those at risk are members of one of the world’s most vulnerable refugee populations. About 1 million Rohingya refugees live in crowded camps in Bangladesh in Cox’s Bazar. The first two coronavirus cases were reported in the camps last week. International aid groups are preparing emergency supplies of food, tarpaulins and water purification tablets.

[Because of climate change, hurricanes are raining harder and may be growing stronger more quickly]

In the Satkhira district of Bangladesh, which is expected to bear the brunt of the cyclone, officials started using loudspeakers to tell people to evacuate on Monday.

On Tuesday, they began going door-to-door to urge them to move to shelters.

Unlike in prior cyclones, authorities are also using schools and mosques with more than one floor as shelters, said Bhabtosh Kumar Mandal, a local official in the Bangladeshi village of Buri Goalini. The goal is to avoid crowds, he said. People have been asked to arrive at shelters with masks, Mandal added. He was racing to collect even more masks to distribute before the cyclone hit.

India recorded over 5,000 coronavirus cases in a 24-hour period ending Monday, the most in a single day, and is nearing the 100,000 mark overall. Ganjam, a coastal district in the state of Odisha, has seen a surge in cases as migrant workers returning home due to an extended lockdown have tested positive. Its neighboring state, West Bengal, saw the highest rise in its virus death toll in early May.

Joanna Slater and Niha Masih reported from New Delhi.