Dangerous Cyclone Amphan in Bay of Bengal Poised to Rapidly Intensify

May 16, 2020, 4:45 PM EDT

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Above: A marooned couple sit on a log close to their home surrounded by the high waters of Cyclone Fani in Khulna, Bangladesh, on May 4, 2019. A strong Category 4 equivalent, Fani made landfall in eastern India with top sustained winds of 155 mph. The storm caused 89 deaths and $8.1 billion in damage in India and Bangladesh. (Munir Uz Zaman/AFP via Getty Images)

The first tropical cyclone of the 2020 North Indian Ocean season, Amphan, formed early Saturday morning and has the potential to become a dangerous hurricane-strength cyclone by early next week. In their 11 am EDT Saturday advisory, the Joint Typhoon Warning Center (JTWC) rated Amphan as a tropical storm with 45 mph winds. The 11 am EDT Saturday advisory from the India Meteorological Institute (IMD) rated Amphan as a cyclonic storm with top winds of 40 mph. The system was moving north at about 3 mph.

Conditions are very favorable for development of Amphan. Wind shear on Saturday was moderate, 10 – 15 knots. Ocean temperatures were exceptionally warm over the Bay of Bengal: 30 - 31°C (86 - 88°F), which is over 1°C (1.8°F) above average. Warm waters extended to great depth in the Bay of Bengal, with a Tropical Cyclone Heat Potential (TCHP) over 100 kilojoules per square centimeter over much of the region. This is a tremendous amount of heat energy, and values of TCHP this high are frequently associated with rapid intensification of tropical cyclones.

Satellite loops on Saturday morning showed that Amphan had taken advantage of these favorable conditions, expanding impressively in areal extent and featuring a large area of heavy thunderstorms that were growing steadily more organized. The system was embedded in a moist atmosphere, though there was some dry air to the west along the east coast of India that could potentially interfere with development.

Forecast for Amphan

The computer models have come into better agreement on Amphan’s future track, though considerable uncertainty in the track can be expected until the storm becomes better defined. The models are united in a mostly northward track for Amphan, with a landfall occurring between 03 and 12Z Wednesday near Kolkata, India, near the border with Bangladesh.

Both JTWC and IMD predicted that Amphan would top out as a category 2 storm with 100 mph winds before landfall. Both of these intensity forecasts are conservative; given the very favorable conditions in the Bay of Bengal, it would not be a surprise to see Amphan intensify into a major category 3 or stronger storm by Tuesday. One of our top intensity models, the HWRF, has consistently been predicting that Amphan will rapidly intensify into a category 4 storm by Tuesday, and continued to do so in its 0Z and 6Z Saturday runs.

Eastern India and Bangladesh still recovering from a 2019 cyclone

Just last year, during the most active North Indian Ocean cyclone season on record, the Bay of Bengal experienced an intense May cyclone: category 4 Tropical Cyclone Fani, which made landfall in eastern India in the state of Odisha on May 2 with sustained winds of 155 mph. Fani killed 89 people and did $8.1 billion in damage in India and Bangladesh, according to insurance broker Aon, making it one of the top-five costliest Indian cyclones on record.

Prior to Fani, the most recent major tropical cyclone to hit India was the 1999 Odisha Cyclone, which hit Northeast India in the Indian state of Odisha (formerly called Orissa) near the city of Bhubaneswar as a Category 4 storm with 155-mph winds on October 29, 1999. The mighty storm, which had been at Category 5 strength with 160-mph winds and a 912 mb central pressure shortly before landfall, drove a storm surge of 26 feet (8 meters) onto the coast. The storm stalled just inland, dumping torrential rains on portions of India already saturated from the landfall of Category 4 Tropical Cyclone 04B just twelve days before. The catastrophe killed 9,658 people and left $2.5 billion in damage (1999 dollars), India's most expensive and fourth deadliest tropical cyclone in the past 100 years.

Two cyclone seasons in the Bay of Bengal

Cyclone season in the Bay of Bengal peaks during April-May and October-November, on either side of the monsoon season. Most of the April and May cyclones in this region move east or northeast toward Bangladesh and Myanmar. In eastern India, most of the worst cyclones have struck during the October-November post-monsoon period. Intense cyclones rarely occur during the peak monsoon period from June – September due to interference from the monsoon circulation.

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.

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Dr. Jeff Masters

Dr. Jeff Masters co-founded Weather Underground in 1995 while working on his Ph.D. in air pollution meteorology at the University of Michigan. He worked for the NOAA Hurricane Hunters from 1986-1990 as a flight meteorologist.


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