Agri Business

Weather: Amphan roars away to super-cyclone status in Bay

Vinson Kurian Thiruvananthapuram | Updated on May 18, 2020 Published on May 18, 2020

Only third pre-monsoon super cyclone in 30 years

Extremely severe cyclone Amphan (pronounced as Um-Pun) over the central parts of the South Bay and adjoining Central Bay of Bengal has spun into a class-topping super cyclone after howling winds around its core broke the threshold speeds. The India Meteorological Department (IMD) announced Amphan’s elevation into a super cyclone status in a tweet.

 

According to IMD’s classification of storms based on intensity, super cyclone is an intense low-pressure system represented on a synoptic chart by more than four closed isobars (concentric circles) and in which the wind speed at surface level is 222 km/hr (category 4 or 5 as per Saffir-Simpson scale storm intensity).

Thresholds broken

This threshold was broken by noon on Monday, even as the storm is almost 1,000 km and two full days away from making a landfall. It is the till-now slow progress and extended stay over the waters that gave it ample space and time to intensify in this manner. The sea-surface temperatures have now eased by a degree Celsius to 31 degree Celsius around the base, but that is more than enough for it to fire away on all cylinders.

Earlier, on Monday morning, the IMD had extended a cyclone warning to North Odisha and West Bengal coasts as part of an ‘orange message.’ Extensive damage is possible to property and infrastructure in West Bengal (East Medinipur, South and North 24 Parganas, Howrah, Hooghli, and Kolkata districts) and in Odisha (Jagatsinghpur, Kendrapara, Bhadrak, Balasore, Jajpur and Mayurbhanj districts).

Destructive strength

Amphan would be only the third super cyclone to form in the Bay after 1990, after the Andhra Pradesh super cyclone (May 4-9, 1990, no name) and the Bangladesh super cyclone (April 24-May 2, 1991, Gorky). The former had hit the Machilipatnam coast in Andhra Pradesh and claimed 967 deaths, while the latter rammed into Chittagong, Bangladesh, killing an estimated 1.38 lakh people.

The destructive storm had kicked up gale winds with speed reaching 180-190 gusting to 210 km/hr over West-Central and adjoining central parts of South Bay of Bengal in the morning. These were expected to accelerate to 220-230 km/hr gusting to 255 km/hr over the northern parts of Central Bay adjoining North Bay from Monday evening, and further to 230-240 km/hr gusting to 265 km/hr in the night.

Fishermen warned

Wind speeds may reach the peak strength of 220-230 km/hr gusting to 255 km/hr over the North Bay from Tuesday morning and gradually decrease to 155-165 km/hr gusting to 180 km/hr by Wednesday. The sea condition would be phenomenal (wave heights of 46 ft and above) over the West-Central and adjoining central parts of South Bay into Tuesday morning. It will be phenomenal also over the northern parts of the Central Bay and adjoining North Bay and over the North Bay the day after (Wednesday).

The only saving grace is that the monster storm would weaken twice as a very severe cyclonic stone before crossing the West Bengal-Bangladesh coasts on Wednesday with maximum sustained wind speeds of 155-165 km/hr gusting to 185 km/hr. Fishermen have been warned against venturing out into the West-Central and adjoining Central parts of South Bay and the Central Bay on tomorrow (Tuesday); and into the North Bay of Bengal from Tuesday to Wednesday.

Rapid, explosive growth

Also, they are advised not to venture into North Bay along and off North Odisha, West Bengal and adjoining Bangladesh coasts from today to Wednesday. Storm surge of 13-16 ft above the astronomical tide may inundate low-lying areas of South and North 24 Parganas and about 10-13 ft over the low-lying areas of East Medinipur District of West Bengal during landfall on Wednesday.

The IMD has been closely tracking Amphan, barrelling across the open waters to rapidly become an extremely severe cyclone by Monday morning. On Monday morning, it located the storm to 790 km nearly South of Paradip (Odisha); 940 km South-South-West of Digha (West Bengal); and 1,060 km South-South-West of Khepupara (Bangladesh). After attaining peak strength by Monday night, it would start to shift track to North-North-East (sparing Andhra Pradesh and Odisha a direct hit) across the North-West Bay and make a landfall over the West Bengal-Bangladesh coasts between Digha (West Bengal) and Hatiya Islands (Bangladesh) by Wednesday afternoon/evening.

Strongest pre-monsoon cyclones (two categories) in Bay Bay of Bengal since 1990

 

Published on May 18, 2020

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