Sea temperature linked to back-to-back cyclones, Yaas landfall awaited

Sea Surface Temperature over Arabian Sea and Bay of Bengal have been ruling at over 31-32°C which is higher than threshold limit of 28°C just before formation of cyclones

The quick succession with which cyclone Tauktae and cyclone Yaas have hit the western and eastern coasts of India has baffled scientists and meteorologists, with many blaming the phenomenon on the speed at which Sea Surface Temperatures (SSTs) have risen first, over the Arabian Sea and thereafter over Bay of Bengal.

SSTs over both seas have been ruling at over 31-32 degree Celsius which is higher than the threshold limit of 28 degrees Celsius just before the formation of the cyclones.

The sharp rise in SSTs has also led to both the cyclones gathering steam in a very short period of time.

“Indian seas have been exceptionally warmer than usual this year, making atmospheric and ocean conditions favourable for the frequent formation of cyclones and their rapid intensification. Rapid intensification is the key point to focus on, as it will have direct impact on rainfall, destruction in terms of floods and gusty winds and evacuation process,” Mahesh Palawat, chief meteorologist at private weather forecasting agency Skymet said in a note published by Climate Trends, a Delhi-based agency that works towards bringing awareness around climate change issues and low carbon development.

The threshold value for sea surface temperatures (SSTs) for the formation of cyclones is 28°C, while at present, SST over Bay of Bengal as well as Arabian Sea is around 31°C - 32°C, the paper said.

“Similarity between Cyclones Yaas and Tauktae is that both are preceded by very high sea surface temperatures reaching 31-32°C. These high temperatures were conducive for cyclone Tauktae to intensify into an extremely severe cyclone very quickly. Similarly, high temperatures are predicted to assist Yaas also for intensifying rapidly,” Dr Roxy Mathew Koll, Scientist, Indian Institute of Tropical Meteorology and Lead Author, IPCC Oceans and Cryosphere said.

However, there is one difference.

Tauktae spent several days in the Arabian Sea where it could draw the heat and moisture continuously, reaching peak intensity of more than 220 km/hr. In the case of Yaas, it has formed in the north Bay of Bengal, and the travel distance to landfall is shorter, Koll said.

He said the common thread in both the cyclones is that the rising ocean temperatures in both the basins are assisting these cyclones in their "rapid intensification" process.

Meanwhile, in related development, both Odisha and West Bengal, the two states that are expected to be worst affected have evacuated over one million people as the cyclone prepares to make a landfall near Dhamra Port in Bhadrak district early on Wednesday morning.

Neighbouring Jharkhand has also sounded an alert and is preparing for the cyclone's impact.

West Bengal Chief Minister Mamata Banerjee on Tuesday said that her administration has evacuated over nine lakh people to safe shelters.

The Odisha government, on the other hand, said it has moved over 200,000 people from vulnerable areas in coastal districts to safety.

IMD Director General Dr Mrutyunjay Mohapatra said that 'Yaas' is likely to intensify into a Very Severe Cyclonic Storm (VSCS) by Tuesday evening.

He said the cyclone's impact will be severe for six hours before and after the landfall and Chandbali will witness the maximum damage.

West Bengal Chief Minister Mamata Banerjee said over 74,000 officers and workers and over 200,000 policemen and civic volunteers have been deployed to mitigate the natural calamity in West Bengal.

She said that National Disaster Response Force (NDRF) and State Disaster Response Force (SDRF) personnel have been deployed and Army's help will be sought if required.

Special Relief Commissioner of Odisha, P K Jena, said that over 210,000 people residing in kutcha houses in low- lying areas have been moved to cyclone shelters.

The highest number of evacuees are from Balasore district (74,132), followed by Bhadrak (73,103).

The South Eastern Railways has announced the cancellation of several passenger special trains till Wednesday.

Hospitals have been asked to ensure alternate arrangements for electricity, oxygen and other essential supplies.

The timing of the storm poses several challenges for already stressed authorities in the country, which is battling a second wave of the coronavirus pandemic. The infections have strained India’s health system and overwhelmed crematoriums and hospitals. They have also spread to rural areas, where about 70% of the nation’s 1.3 billion people live.