Unusual formation due to the warming of the Bay of Bengal basin; protracted gestation could lead to its gaining strength

Cyclonic storm Fani, which is lying about 600 km east of Vishakapatnam and 800 km south of Puri, is the first severe, cyclonic storm to have formed in April in India’s oceanic neighbourhood since 1976, according to records from the India Meteorological Department (IMD).

While severe cyclones (defined as generating maximum windspeeds of 89-117 kmph) can form any time, they tend to be concentrated in November — after the monsoon — or around May, when the monsoon prepares to arrive in Kerala in June.

The head of IMD told The Hindu that such quirks were a consequence of global warming. “This is a cyclone that’s forming due to the warming of the Bay of Bengal basin…with global warming we have to be prepared for such occurrences and take precaution accordingly,” said K.J. Ramesh, Director-General, IMD. He said that Fani, so far, was unlikely to have an impact on the advent of the monsoon.

From 1965-2017, the Bay of Bengal and Arabian sea have collectively registered 46 ‘severe cyclonic storms.’ As many as 28 of them were from October-December. Seven of them have been in May and only two — in 1966 and 1976 — were recorded in April, data from the IMD’s cyclone-statistics unit shows.

Tropical cyclones in the Indian neighbourhood begin as ‘depressions’ or a gradual build-up of warm air and pockets of low pressure. About 35% of such formations intensify to ‘cyclones’ and only 7% intensify to ‘very severe cyclones’. About 20-30 severe tropical storms occur around the world every year.

The IMD ranks cyclones on a 5-point scale with the mildest at 62-88 kmph and the strongest, a ‘super cyclonic storm’, at 221 kmph). Cyclone Fani is expected to graduate to an ‘extremely severe cyclonic storm’ by Wednesday and make landfall in Orissa (as a very severe cyclonic storm) by May 4, according to an evening forecast by the IMD on Tuesday.

“It is very likely to move northwestwards till May 1 evening and thereafter re-curve north-northeastwards and reach Odisha Coast by May 3 afternoon with maximum sustained wind of speed 170-180 gusting to 200 kmph,” the IMD statement notes.

Meteorologists also point to Fani’s protracted gestation. The storm had been building up since April 25 and is expected to make landfall, according to current models, only by May 3. “Nearly 10 days is an extremely long period,” said Mr. Ramesh. On an average tropical cyclones form and make landfall in less than a week.

Satheesh Shenoi, Director, INCOIS (Indian National Centre for Ocean Information Services), a research unit responsible for tracking the oceans, said that Fani’s slow progress — it is now moving at 11-18 kmph — was also a matter of worry as the longer it hovered in the ocean, the more moisture and energy it gained from the ocean and the stronger its impact along the coast. “For now, models suggest that waves as high as 6.3 m are possible in the ocean under the influence of the storm,” he told The Hindu.

Heavy rains are expected in north Andhra Pradesh and Odisha and light rains in West Bengal under the influence of the cyclone. Strong winds are expected in Kerala, Tamil Nadu, Puducherry and south Andhra. Fishermen have been advised to stay away from the sea.