Several parts of the city and its northern and southern fringes received thunderstorms, which brought temporary relief from the sultry conditions, late on Monday.
What started as strong gusts of wind and streaks of lightning gave way to rain.
Many hundred kilometres away, a cyclonic circulation is set to take shape over the Bay of Bengal on Wednesday, said Met officials.
The timing has set off a flurry of posts on social media about its possible intensification into a cyclone. The fear has its footing in history. The month of May has consistently offered what Met officials call the “best climatological conditions” for a weather system to intensify into a cyclone.
Five years ago, on May 13, satellite images showed the “remnant of a low-pressure area” over the south Andaman Sea and adjoining southeast Bay of Bengal. The system snowballed into Amphan, one of the fiercest cyclones on the Bay that ravaged coastal Bengal and Calcutta on landfall near the Sunderbans on May 20, 2020.
The Met office has not issued any such alert so far.
“A cyclonic circulation in the upper air is likely to take shape over southeast Bay of Bengal around May 14. As of now, there is nothing more to it,” said a Met official.
An extended-range IMD forecast last week also predicted a “low to medium” probability of a cyclogenesis (the process of development and intensification of a system, often leading to a cyclone) on the Bay in the second week of May.
“In May, the sea surface temperature is on the warmer side. A storm draws on the heat and moisture to gain strength on the sea. A strong vertical wind shear can be detrimental for a cyclone. But at this time of the year, the wind shear is unlikely to be very strong,” said a retired Met official.
Last year, between the night of May 26 and the morning of May 27, Cyclone Remal landed in the Sunderbans in Bangladesh. In the 24 hours between May 26 and 27, Calcutta was battered by around 190mm of rain, among the heaviest it had seen in the past few years.
Met officials said any comparison was premature. “The circulation will take shape far away from the Bengal coast. What happens to the system depends on a host of factors,” said one of them.
Monsoon
A Met bulletin issued on Monday said southwest monsoon was at the threshold of the southernmost tip of India.
“Conditions are favourable for advancement of southwest monsoon into some parts of the Andaman Sea, south of Bay of Bengal and Andaman and Nicobar Islands by May 13,” it said.
The normal date of the monsoon’s advance over Kerala is June 1 and the Northeast June 5, based on long-term weather data.
The monsoon moves across the subcontinent in phases, covering Bengal, eastern and central India by June 15 and reaching Delhi and northwestern India by June 30.
Heatwave
South Bengal is still reeling under the twin assault of heat and humidity.
In Calcutta, the maximum temperature dropped marginally to 38.6 degrees on Monday. It was still three notches above normal.
The humidity quotient was still high and people sweated profusely.
Dum Dum saw a maximum temperature of 40.3 degrees on Monday.
At the same time, thunderstorms are also likely to continue in some parts of the state.
Earlier in the day, the Met bulletin said: “Mainly dry westerly to north westerly winds are likely to prevail at lower levels over the region and consequently hot andhumid conditions are likely over the districts of south Bengal. Heatwave conditions are likely over some districts of west Bengal. A trough runs from central parts of Bihar to south Jharkhand and extends upto 1.5km above mean sea level.”
“In view of availability of moisture and heating impact, possibility of enhanced thunderstorms with heavy rainfall activity is likely over some districts of north Bengal and isolated thunderstorm activity is likely over some districts of south Bengal.”
An official at the Regional Meteorological Centre in Alipore said: “Thundershowers are likely in several districts, including South and North 24-Parganas, on May 13 and 14 as well. Since the two border the city, some rain is not ruled out here.”