Many tropical cyclones in recent years have undergone rapid intensification, such as super cyclone Amphan which hit West Bengal and Bangladesh in May 2020
Several news reports have speculated the formation of a super cyclone in the Bay of Bengal and its potential landfall along the eastern coast.
The India Meteorological Department (IMD) has urged citizens not to believe them, but it will start tracking low-pressure area forming in the Bay of Bengal October 20.
A cyclonic circulation has formed over the southern Andaman Sea and its neighbourhood, said the weather agency in a cyclone update issued October 17, 2022.
This cyclonic circulation, swirling winds in the upper levels of the atmosphere, may induce a low-pressure area in the southeast and east central Bay of Bengal October 20.
After formation, the storm system will likely move west-ward and north-westward into west central and neighbouring southwest Bay of Bengal. IMD predicted that the low-pressure area would become slightly more intense in the subsequent two days.
It did not say anything about further intensification into depression or a cyclone. The conditions for cyclogenesis do exist in the region.
“Now we have a La Niña in the Pacific. La Niña conditions are favourable for cyclone formation and intensification in the Bay of Bengal, as compared to El Niño years,” said Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology. He is also the lead author at the Intergovernmental Panel on Climate Change.
Winds have changed to a northeast pattern and the rainfall trends over the Arabian Sea and the northern Bay of Bengal for October will favour cyclogenesis, said Raghu Murtugudde, a climate scientist at the University of Maryland and Indian Institute of Technology, Bombay.
The forecast does seem to indicate tightening and strengthening of cyclonic system. He added that one has to watch for the standard issues now — the possibility of rapid intensification and the potential tracks.
Rapid intensification is when a tropical cyclone’s maximum sustained wind speeds increase by more than 55 kilometres per hour (kmph) in 24 hours. It generally happens due to warm ocean waters and conducive wind conditions over the ocean area where the cyclone is forming.
Many tropical cyclones in recent years have undergone rapid intensification, such as Super Cyclone Amphan which hit West Bengal and Bangladesh in May 2020.
It went from being a severe cyclone (with wind speed 89-117 kmph) to a super cyclone (with wind speed above 222 kmph) in 24 hours. This happened because of exceptionally warm waters in its path in the Bay of Bengal, showing the impact of ocean warming due to human-induced emissions of greenhouse gases.
Amphan also grew to an incredible size and gained considerable strength, becoming the strongest cyclone in the Bay of Bengal since the Odisha super cyclone in 1999. It was also the costliest cyclone in the Indian Ocean region, with a loss and damage bill of around $13 billion.
Extremely severe cyclone Tauktae also experienced rapid intensification by gaining around 83 kmph wind speed in 24 hours in May 2021. It was one of the strongest cyclones to impact the west coast of India.
Tauktae had maintained cyclonic strength (at least 62 kmph) for 18 hours over land, which was highly unusual as moisture that fuels cyclones is not easily available on land. This shows the impact of global warming.
It also tracked as a storm to Delhi, causing rainfall and bringing down temperatures of the capital city by more than 10 degrees Celsius in May.
“But I would hesitate to go as far as saying whether the current cyclone will grow into a super cyclone,” said Murtugudde.
False alarms can be even more damaging than wrong forecasts. So, we have to be careful, he warned.
“As of now, the Bay of Bengal is warm (29°C and above) and humid. The monsoon wind shear is weak. It means that the basin can support the formation of a depression or a cyclone,” said Koll.
However, the sea surface temperatures are not exceptionally warm to support the rapid intensification of cyclones, he added.
The fact that the monsoon winds have not yet withdrawn from India may also influence the formation and intensification of the cyclone.
The monsoon has retreated from the northwest and many parts of central India and some parts of east and northeast India as of October 17, according to IMD. The withdrawal is already late by two days.
“We might need to wait a few more days for a clearer forecast (for the cyclone), since the withdrawing monsoon can interact with the Bay of Bengal conditions and cyclogenesis,” said Koll.
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