Cyclone Nisarga is expected to make landfall on Maharashtra's coast on 3 June | Image: IMD

Cyclone Nisarga makes landfall in Maha; clear links to warming Arabian Sea

A red alert has been issued by the India Meteorological Department (IMD) for the first cyclone in June to make landfall in Mumbai in 129 years. Cyclone Nisarga, according to the IMD, made landfall between Alibaug and Mumbai around 1pm on June 3 with sustained wind speeds of 100-110 kmph and gusts of about 120 kmph.

The MET department expects the cyclonic storm to maintain intensity for about 6 hours after making landfall while it traverses the western coast towards Gujarat. Low-lying areas of Mumbai, Raigad, Thane and Ratnagiri have been put on alert for inundation due to a likely storm surge 0.5-2m beyond the astronomical tide levels from the storm. Fishermen have been advised not to venture out to sea as more than 21,000 people from low-lying villages in Palghar district have been evacuated. Another 20,000 vulnerable people from Gujarat’s coastal villages are also being evacuated in preparation for the cyclone. The National Disaster Response Force (NDRF) is on standby with 33 teams in place across the two states. Four and six teams of the State Disaster Response Force (SDRF) have also been deployed in Maharashtra and Gujarat respectively.

Nisarga is the second pre-monsoon cyclone to hit the subcontinent’s coasts, about two weeks after Cyclone Amphan battered the Gangetic delta in the east coast around West Bengal and Bangladesh. The Arabian sea hosted record cyclone activity in 2019 with four cyclones forming off the coast of India during the year as compared to the long-term average of just one. While most of the increase has been attributed to a rise in the post-monsoon cyclone season during October-November, cyclone formation over the past few years indicates a detectable increase in the pre-monsoon season as well. While Nisarga makes its way towards India, another low-pressure area, that is likely to move towards the Arabian peninsula, has already formed over the Arabian Sea. The Arabian Sea has already birthed one significant low depression in May this year, bringing records levels of rain to Oman and causing the deaths of at least three people.Scientists believe the recent increases of tropical cyclone activity in the north Indian Ocean are a part of the global pattern of increasing cyclone frequency, intensity and duration due to warming trends in Earth’s atmosphere and seas. The intensity of cyclones, in particular, is linked heavily with sea surface temperatures as cyclones are fueled by available heat, and are hence made stronger by warming oceans. A recent study found that warming oceans had increased the proportion of the strongest and most destructive cyclonic storms by 8% over a 39-year period. The strength and rapid intensification of Amphan, which hit India’s east coast and Bangladesh in May, have been linked to high sea-surface temperatures in the Bay of Bengal. The Arabian Sea, which usually seas an average surface temperature of 28-29.5 degrees Celsius in May-June, has also recorded similar deviations from the normal in the run up to the development of Nisarga.

Sea-surface temperatures in the Arabian Sea were observed to be around 3.5 °C above normal on 29 May 2020, as Cyclone Nisarga rapidly built up | Image: NASA/ Null School

“In the case of both the recent cyclones — Amphan and now Nisarga — the anomalously warm ocean temperatures are proving to give them a major boost. While temperatures in the Bay of Bengal were between 30-33°C prior to Amphan, surface temperatures over the Arabian Sea was recorded at 30-32°C prior to the depression, which is now evolving into Cyclone Nisarga. Such high temperatures aid rapid intensification of these cyclonic systems, which many weather models fail to capture,” says Indian Institute of Tropical Meteorology (IITM) scientist Roxy Mathew Koll, who is also a lead author with the Intergovernmental Panel on Climate Change (IPCC).

While the IMD has said that the cyclone will aid the monsoon, a similar formation in 2019, Cyclone Vayu, ended up disrupting monsoon progress for around two-weeks after onset. This year, the IMD announced monsoon onset over Kerala on June 1.

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