Nisarga, a possible severe cyclonic storm that is expected to result from a depression forming in the southeast and adjoining east-central Arabian Sea and Lakshadweep area will impact Mumbai city which may experience high speed winds and extremely heavy rainfall, the India Meteorological Department (IMD) said Monday as it issued a red alert for six other districts including Palghar, Thane, Raigad, Dhule, Nandurbar and Nashik between June 3 and 4.

On Monday, the depression lay 310 km southwest of Panjim in Goa, 570 km south-southwest of Mumbai in Maharashtra and 800 km south-southwest of Surat in Gujarat. The depression is likely to move northwards till June 2 morning and then re-curve north-northeastwards and cross north Maharashtra and south Gujarat coasts during June 3 afternoon, which is when it is likely to make landfall. As per the current IMD forecast, the entire region between Daman (near Gujarat) and Harihareshwar in Raigad — comprising the Konkan coastline, which encompasses Mumbai — as well as some inland districts of Maharashtra, stand to be affected. However, the next 48 hours may bring further changes to the forecast Sunitha Devi, in-charge of cyclones at the IMD, said.

"The landfall is expected towards the south of Mumbai. Since the Arabian Sea system is dynamic there are a few predictability issues. There might be further changes in the coming 48 hours depending on how the [weather] system moves," she said. "An orange alert (to be prepared) will be issued 48 hours before the landfall while a red alert (to take action) will be issued 12 to 24 hours for the affected areas," she said.

Also read: Here's how to live track Cyclonic storm Nisarga

"It will pass over this region as a severe cyclone but there is a marginal reduction in wind speed expected. Mumbai is likely to experience high speed winds as the cyclone makes landfall south of the city," Devi said.

"We haven't given an exact location of landfall yet. It will be shared as soon as reliable information is available but Mumbai will be impacted," M Mohapatra, director general, IMD confirmed.

Scientists said that Nisarga, which is likely to make landfall on June 3 afternoon could inundate low lying areas especially in cities like Mumbai and cause structural damage from falling trees and power poles. This has raised concern over how the city, already strained for healthcare resources on account of the Covid-19 pandemic, will cope. What's more, each year the monsoon brings the city to a halt as train lines, streets and drains get flooded leaving lakhs of commuters stranded for hours.

A red alert — which indicates the possibility of extremely heavy rain of more than 204.5 mm — is a warning for residents to take action and keep safe from adverse impact. It has been sounded for seven districts including Mumbai for Wednesday, and additionally on Thursday for Palghar. An orange alert has been sounded for Mumbai and Thane for Thursday.

"The wind speed along with rough sea conditions in the landfall region will be capable of damaging weak structures such as huts, and thus affect poor people and fishermen who live on the coastline," Akshay Deoras, independent meteorologist and doctoral researcher at the University of Reading, United Kingdom, said.

While it is still early to ascertain where the storm might make landfall, the experience of cyclone Amphan — which the eastern coastline on May 21 and left 86 dead as well as millions homeless — is still fresh in national memory. "In the interest of public safety, local evacuation is advisable in such areas, which is likely to be challenging in the ongoing Covid-19 scenario." Mumbai is facing a severe healthcare infrastructure crunch as hospitals and care facilities are unable to cope with the high number of cases, which stood at 41,099 cases as on June 1.

"Central and state government agencies are trying to take all steps possible to prevent damage. We are specially advising fishermen in Maharashtra, Kerala, Coastal Karnataka, Gujarat, Goa, Lakshadweep to avoid going to the sea till June 4. Those out at sea should return immediately as sea can be very rough from now on," Mohapatra said.

According to the IMD bulletin, the system is expected to become a cyclonic storm by 11.30 am and a severe cyclonic storm by 5.30 pm on June 2. It is likely to make landfall by Wednesday afternoon. The wind speed is expected to be 105-115 kmph gusting to 125 kmph over east-central and northeast Arabian Sea along and off Maharashtra coast.

"It is very unusual for a cyclone to make landfall in or near Mumbai or even on the Maharashtra coast. The storms that form during monsoon onset over Arabian Sea usually move towards Oman. Cyclone Phyan had impacted these districts in 2009 and even Mumbai had recorded extremely heavy rains," Devi said.

With the formation of two cyclones — in the Bay of Bengal (Amphan) and Arabian Sea (yet to be formed Cyclone Nisarga) — within two weeks of each other, scientists warn about the possibility of more pre-monsoon cyclonic storms in coming years due to warmer ocean temperatures.

Dr. Roxy Mathew Koll, senior scientist, Indian Institute of Tropical Meteorology (IITM) Pune said, "We already see a detectable increase in the number of post-monsoon tropical cyclones over the Arabian Sea— and we need to ask if we are we moving towards a similar trend during the pre-monsoon also. We don't know yet if this is part of a rising trend."

Scientists argue that anomalously warm ocean temperatures have aided in the genesis and rapid intensification of recent cyclones. The sea surface temperature in the Arabian Sea presently is as high as 32°C compared to a normal of 28°C expected during this season.

However Mohapatra said that other parameters also need to be considered in the case of the expected cyclone.

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