Cyclone Nisarga may hit Mumbai on June 3, says weather department

Nisarga will be the first cyclone to hit the Maharashtra coast in June since 1891, according to the weather department  

By Akshit Sangomla
Published: Monday 01 June 2020
The Cyclone Nisarga system lay as a depression around 340 kilometres south west of Panjim and 630 km south-south west of Mumbai at 11.30 am on June 1 Photo: Twitter / @Indiametdept

Cyclone Nisarga may make landfall near Mumbai on June 3, 2020, bringing strong winds, heavy rain and a possible storm surge to the city before the monsoon season begins in the region, according to the India Meteorological Department (IMD).

The southwest monsoon season reached Kerala on June 1, the IMD said.

The system lay as a depression around 340 kilometres south west of Panjim and 630 km south-south west of Mumbai at 11.30 am on June 1. It will intensify into a cyclone on June 2 evening, after which it will move north to begin with, but recurve north east to the Maharashtra coast.

Nisarga will be the first cyclone to hit the Maharashtra coast in June since 1891, according to data from the IMD. 

Cyclone Vayu formed in June last year and was set to make landfall along the Maharashtra coast for a while. The cyclone, however, moved towards Gujarat.

Most of the June cyclones in the past have either moved to the Gujarat and Pakistan coasts or further west to Oman and Yemen.

The European Centre for medium-range weather forecasts predicts the cyclone will lose some intensity after it makes landfall, but will move further inland as a depression towards Maharashtra and Madhya Pradesh, causing rainfall.

When the monsoon onset happens, south westerlies become strong and go several kilometres up from the surface, said Raghu Murtugudde, climate scientist at the University of Maryland, US.

As the cyclone moves north along the coast, its counter-clockwise winds enhance the south westerlies to its south, feeding itself and growing, along with moving further north, Murtugudde pointed out.

“Depending on the energy it has and its extent over the ocean, it may remain active quite far onto land before losing steam and dying away,” he added.

Cyclones generally form and move over warm sea water with temperatures greater than 27 degrees Celsius (°C). Their track usually indicates warmer sea surface temperatures and low vertical wind shear (change in winds in the vertical direction) the areas which they pass, allowing the cyclone to suck in moisture and grow.

During Cyclone Amphan, sea surface temperatures were around 32-33°C — one of the highest-ever recorded — which allowed the cyclone to become the strongest one recorded in the Bay of Bengal through rapid intensification.

Some scientists also attributed Amphan’s strength and rate of growth to decreased aerosol emissions resulting from the lockdowns in south Asia to curb the spread of the novel coronavirus disease (COVID-19) pandemic.

Aerosols in the atmosphere generally cause premature rainfall which does not allow the cyclone to increase in intensity. Similar reduced aerosol conditions are present in the case of Nisarga.

Amphan surprised the residents of Kolkata with its wind speeds of 130 kmph. Mumbai seems to be in Nisarga’s path.

It is the second cyclone in the North Indian Ocean (NIO) region this year after Amphan in the Bay of Bengal, which made landfall along the Sunderbans region of West Bengal on May 20 and caused heavy destruction in the coastal areas of south Bengal and Kolkata.

“In the case of both the recent cyclones — Amphan and now Nisarg — the anomalously warm ocean temperatures aided their genesis and rapid intensification,” said Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology, Pune.

Ocean surface temperatures were consistently above 30°C prior to the formation of both the cyclonic systems, sometimes crossing 32 or 33°C, Koll said.

“Such high temperatures aid rapid intensification of these cyclonic systems. Many weather models, however, fail to capture this rapid intensification due to high temperatures, which is why we have a hard time predicting it accurately,” he said.

According to him the atmospheric conditions over the Indian mainland will take some time to settle down after the cyclone and this might lead to a lull in the progression of the southwest monsoon.

Last year, the Arabian Sea recorded five cyclones out of the total eight in the NIO region, the highest since 1902.

This indicated the Arabian Sea was warmer than usual in 2019. The highest ocean heat content ever recorded was also witnessed last year.

This is a direct consequence of global warming as 90 per cent of the heat trapped by greenhouse gas emissions goes into the world’s oceans.

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