Amphan Pushing Wind, Rain, and Potentially Fierce Surge into Eastern India and Bangladesh

May 20, 2020, 5:26 AM EDT

Above: Enhanced infrared image of Tropical Cyclone Amphan nearing landfall in far eastern India at 0200Z (7:30 am EDT) Wednesday, May 20, 2020. (CIMSS/SSEC/UW-Madison)

Outer rainbands of Tropical Cyclone Amphan were lashing the east coast of India on Wednesday morning IST as the sprawling storm headed for a Wednesday-evening landfall just south of Kolkata. At 00Z Wednesday (8:30 am IST), the Joint Typhoon Warning Center rated Amphan’s top (1-minute) sustained winds at 95 knots, making it a high-end Category 2. Amphan was centered about 240 miles south-southwest of Kolkata or about 180 miles south-southwest of the West Bengal coast, moving north-northeast at about 10 mph.

Update: According to JTWC analyses, Amphan made landfall as a strong Category 1 or low-end Category 2 storm between about 10Z and 11Z Wednesday (6:30-7:30 pm IST) on the coast just southwest of Kolkata. The center moved over eastern parts of the Kolkata area between about 12Z and 14Z Wednesday (8:30-10:30 pm IST).

Even on the weaker west side of Amphan, the Indian state of Odisha was feeling the storm’s power. Winds gusted to 66 mph at Paradeep around 01Z (6:30 am IST), with a 24-hour rainfall total of 208 mm (8.19”) through 02Z, according to IMD.

With much of the western side of Amphan’s circulation inland across Odisha, and with wind shear on the increase, Amphan’s top winds were predicted weaken a bit more by landfall. However, Amphan continues to pose a major storm-surge threat to coastal areas of India’s West Bengal province and western Bangladesh. Amphan has been pushing immense amounts of water toward the northern end of the shallow Bay of Bengal since its rapid intensification into a large Category 5 cyclone on Sunday into Monday local time. There is a great deal of momentum in the surge pushed by large, powerful storms like Amphan as their peak winds weaken but their overall wind fields expand, as evidenced by 2008's Hurricane Ike in Texas and 2012's Hurricane Sandy in New Jersey and New York.

Forecast for Amphan’s landfall

Models and agency forecasts agree that Amphan will accelerate north-northeast and should be making landfall around 12Z Wednesday (5:30 pm Wednesday IST), probably near or just east of the mouth of the Hooghly River south of Kolkata. Much of the worst surge will plow into the Sundarbans, a large coastal mangrove forest preserve that is sparsely settled by regional standards. Still, many people around the Sundarbans could feel Amphan’s surge impacts.

If Amphan’s center arrives near or just west of the mouth of the Hooghly River, it may drive a large surge some distance upriver. Tidal forecasts for Sagar Island, located where the Hooghly River meets the Bay of Bengal, show a low tide at 2:46 pm and high tide at 8:32 pm, so Amphan may arrive roughly in between low and high tide, but atop an increasing tide. The tidal range at Sagar Island is substantial—about 3 meters (9.8 feet).

At Diamond Harbour, about 30 miles inland and 20 miles south of central Kolkata, low tide is at 5:05 pm and high tide at 9:48 pm. The tidal range at Diamond Harbour is exceptionally large—about 4.5 m (15 ft)—so the exact timing and location of Amphan’s arrival will make a huge difference in any tidal effects here. IMD predicts that the surge at Diamond Harbour could range from 0.5 to 3.2 m (1.6 to 10.5 ft) atop astronomical tides. Coastal surge could be as high as 4.6 m (15 ft), according to IMD.

Amphan will be moving steadily once inland, so rainfall amounts will not be titanic, perhaps reaching the 8” to 12” range locally. That said, the Kolkata area has been plagued by rising sea level and struggling infrastructure, so episodes of localized flooding well inland are certainly possible.

The challenge of evacuation in the COVID era

Thousands of evacuees in eastern India and Bangladesh were forced to confront the coronavirus pandemic even as they sought refuge. All those in Bangladeshi shelters were being asked to wear masks, reported the Dhaka Tribune. More than 12,000 cyclone shelters in Bangladesh had been prepared for evacuations on Tuesday, including 5000 dedicated shelters and more than 7000 schools being brought into service.

“Cyclone Amphan is a crisis on top of a crisis,” said Pankaj Anand, director of programs and humanitarian response for Oxfam India. “Many of the cyclone evacuation shelters are already being used as coronavirus quarantine centres or housing migrants who have returned to their coastal communities because of lockdown. People are worried there won’t be enough space in the shelters and that they might catch coronavirus in them.”

A weather.com roundup has more on Amphan's impacts.

Amphan’s less impressive twin: Invest 98S

The same weather feature that helped give birth to Amphan also nurtured a twin cyclone on the other side of the equator, Invest 98S. Such twins are a not-infrequent consequence of strong westerly wind bursts along the equator. These contribute low-level spin to cyclones on either side of the equator (since cyclones rotate counterclockwise to the north and clockwise to the south).

“Of course westerly wind bursts occur all the time in the Indian Ocean, but this event is particularly intense & widespread,” tweeted Philippe Papin (Naval Research Laboratory). The westerly wind burst is associated with a strong phase of the Madden-Julian Oscillation; if it makes it into the central and eastern Pacific in a few days, it could reinforce the current trend toward La Niña development.

Fortunately, 98S will encounter cooler water and much stronger wind shear a couple of days from now, long before it has a chance to reach western Australia, though it could arrive as a named tropical storm.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

author image

Bob Henson

Bob Henson is a meteorologist and writer at weather.com, where he co-produces the Category 6 news site at Weather Underground. He spent many years at the National Center for Atmospheric Research and is the author of “The Thinking Person’s Guide to Climate Change” and “Weather on the Air: A History of Broadcast Meteorology.”
 

emailbob.henson@weather.com

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