CHENNAI: The Indian Meteorological Department (IMD) on Saturday announced that there is a new low pressure area over the southeast Bay of Bengal, which would intensify into a depression in the next 48 hours.
N Puviarasan, director of Area Cyclone Warning Centre at Regional Meteorological Centre, said the weather system has formed over south Andaman sea and neighborhood. "It is likely to concentrate into a depression during the next 48 hours and move towards South Tamil Nadu."
This comes barely two days after the very severe cyclonic storm Nivar made landfall dumping copious rainfall in the coastal districts of the state. Officials said heavy to very heavy rains are likely to occur at isolated places over South Tamil Nadu from December 1. Meanwhile, overcast conditions would continue in Chennai with maximum and minimum temperatures of 30 degrees and 22 degree Celsius respectively.
Experts say a growing proportion of tropical cyclones are developing quickly, known as rapid intensification. According to multiple studies, these changes are linked with climate change. Warm ocean waters are one factor driving rapid intensification, which is a threat because it makes it harder to forecast how a storm will behave and so to prepare before it makes landfall.
A recent study concluded that “ocean surface and subsurface conditions played a vital role in the genesis and intensification of cyclone Ockhi”, a very similar cyclone that hit Tamil Nadu almost exactly three years ago, causing 844 deaths. The study found that unusually warm ocean temperatures evolved from a depression to cyclone in 9 hours and then to a very severe cyclone in 24 hours.
Similar to other parts of the world, sea surface temperatures in the Bay of Bengal have been steadily increasing over the last decades.
In addition, tropical cyclones in the Bay of Bengal are affected by the El Niño–Southern Oscillation (ENSO), a meteorological phenomenon that affects wind patterns and sea surface temperatures in some regions of the Pacific Ocean with consequences in different parts of the world.
Scientists have found a correlation between the cooler phase of ENSO, known as La Niña, and increased tropical cyclone activity in the Bay of Bengal.
Roxy Mathew Koll, Scientist at the Indian Institute of Tropical Meteorology and Lead Author on the IPCC Oceans and Cryosphere report, told The New Indian Express, "Now, we have a La Nina in the Pacific, that is cool conditions in the Pacific that makes the local environmental conditions favorable for cyclogenesis in the Bay of Bengal. During the last 40 years, six cyclones - of the severe cyclone category- hit the Tamil Nadu coast in November. Out of these six, five of them coincided with La Nina like conditions in the Pacific. So that means to some extent we were expecting a cyclone season in the Bay of Bengal during this time - and it is not a surprise."
The Bay of Bengal is part of the warm pool region, where the temperatures are generally about 28-29 degrees Celsius in November and occasionally exceeding 30 degrees. These high temperatures are generally conducive for cyclogenesis. "On top of that the global warming element is there - this time the temperature anomalies are about 0.5-1 degree and in some regions reaching 1.2 degrees, based on buoy and satellite estimates. Every 0.1 degree means additional energy for the cyclone to maintain and develop. Locally, the winds are also favoring cyclone formation. The Madden Julian Oscillation (MJO) - that is a band of eastward moving cloud bands - is currently active south of Bay of Bengal. So with favorable ocean-atmospheric conditions leading to cyclogenesis and a climate change element assisting storms rapid intensification," he said.
Intergovernmental Panel on Climate Change (IPCC) scientists have been warning about such events. The most recent report that covered Oceans and Cryosphere clearly warned that if global warming is not stopped, there would be a rise in these events, both in number and in the severity of cyclones.
Since the beginning of 2020, Cyclone Nivar was the 8th system in the Indian Ocean and the Bay of Bengal. Out of these eight recorded incidences of cyclones, Amphan and Nisarga were super cyclones while Gati and Nivar are considered very severe cyclonic events. There were four relatively smaller depressions this year that also caused heavy rains and increased wind velocity. In 2019, there were 12 storms.
Among all the coastal states, Tamil Nadu is one of the worst affected. According to IMD data, the number of storms that hit Tamil Nadu from 1890 to 2002 was 54. Tamil Nadu experienced 10 storms in 16 years from 2002 to 2018, which is an increase of 30 per cent. During the last six years (2014-2020), there were five storms -- Thane, Ockhi, Vardah, Gaja and Nivar.