New Delhi: The powerful Cyclone Fani which ravaged the eastern coast of India was the longest-lasting cyclone in April over Bay of Bengal in a century, said the India Meteorological Department (IMD).
“It was the longest-staying system over Bay of Bengal in April, from 1901. It travelled from 4 degree north of equator to 20 degree north of equator in almost 11 days. A life cycle of 11 days for a cyclone in April has not been seen since 1901," said Dr K J Ramesh, Director General of Meteorology (DGM), IMD.
The slower a cyclone travels and longer it remains over the sea, the more intense it becomes.
Cyclone formations are not unusual in April, which is part of the normal cyclone season for North Indian Ocean, especially Bay of Bengal. However, very extreme Cyclone Fani which made its landfall near Puri in Odisha on Friday morning, as predicted by IMD, was one of the strongest to have been recorded since the Super cyclone 1999 and Cyclone Phailin in 2013, killing at least 16 in India and causing evacuation of a million.
Normally, the systems formed over Bay of Bengal stay for around four days and once formed, they move in north-west direction towards Tamil Nadu, Andhra Pradesh, Odisha or occasionally towards West Bengal. In any case, they take maximum five days. However, the current system lasted over 11 days, and widened its lateral extent.
Scientists warn that global warming is fuelling intense systems over the Indian Ocean.
“Cyclones derive their energy from warmer seas. We have been observing an accelerated warming of the Indian Ocean and it’s leading to intense systems. This is manifestation of climate change," said the senior scientist.
The land has already become warmer by 0.8 ° C, now the ocean is also showing over 0.5 ° C warming. Since, Cyclone Fani was the first system to be formed in the summer season; it derived higher coupled energy from a warmer atmosphere and warmer ocean.
Unlike Cyclone Ockhi which battered the southern coast in December, 2017 and left meteorologists with difficulties in forecasting its intensity due to its rapid intensification, the weather department was well-equipped to meet the challenge this time and issued accurate forecasts.
After Ockhi, IMD began using the coupled ocean-atmosphere coupled models, developed in support with the Indian National Centre for Ocean Information Services (INCOIS), which made the forecast of cyclones and its intensity more accurate.
“There are prescribed value of sea-surface temperatures. These values are indicative of how much energy ocean can contribute to the system. But actually when the cyclone passes over the ocean, the sea-surface temperatures change, which explains how much energy was exchanged. The previous cyclone models were only atmospheric, did not have an active ocean component. Now we have a coupled model, which includes both-ocean and atmosphere component," said Dr S C Shenoi, Director, INCOIS.
The quantum and frequency of satellite data updation has also gone up enormously in last six months. Apart from satellite data from INSAT which is upgraded after every half an hour, more data is available from European satellite over Arabian Sea and those from China and Japan over the Bay of Bengal tracking the cyclone which changes very rapidly.
The first indication of a system comes from the global models which are usually run at 12km grid scale twice a day for next ten days. These models pick up a system from the stage of a low-pressure itself. So, when the system is confirmed during the four runs of the model over the two days consistently, its development and intensification is studied using the cyclone scale models. The 3×3 kms grid models are being run at the finest scale and resolution for Indian Ocean, said officials.
The IMD had been tracking the system ever since it was formed in south-western Bay of Bengal and had been issuing regular updates forecasting its intensity and the projected path.