A rise in moisture incursion from the Bay of Bengal has prompted the Met office to issue an “enhanced thunderstorm” alert for Bengal from April 29 to May 3.
The thunderstorms are likely to be marked by frequent streaks of lightning, strong gusts of wind, sharp spells of rain and, in some places, hailstorms, Met officials said.
“In anticipation of the approach of upper air westerly trough and moisture incursion from Bay of Bengal, enhanced thunderstorms with lightning activity along with gusty wind likely over the districts of West Bengal during April 29 to May 3,” said a bulletin issued on Friday afternoon.
“Kolkata is likely to get more than one spell of thunderstorm in the coming days,” said a Met official.
Thunderstorms do not necessarily mean heavy rain. But tall and powerful cumulonimbus clouds have triggered a downpour in Kolkata several times.
Even if it does not bring heavy rain, the thunderstorms can cause large-scale damage by uprooting trees and poles and causing electrocution.
According to the bulletin, thunderstorms are likely in all the districts from Saturday to Wednesday.
On Saturday, the accompanying gusts of wind are likely to clock up to 40kmph. On Sunday and Monday, the wind speed is likely to go up to 50kmph.
Districts like Birbhum, Purulia, Bankura, Purba and Paschim Bardhaman, Murshidabad and Nadia are likely to get hailstorms on Sunday and Monday.
In north Bengal, heavy rain is expected in Darjeeling and Kalimpong, Jalpaiguri, Coochbehar and Alipurduar districts in the coming days, in addition to streaks of lighting and gusts of wind.
Under the influence of two Western Disturbances over Pakistan, a trough line has taken shape. The trough is expected to move eastwards in the coming days, said Met officials.
“The trough line, combined with increased moisture incursion from the Bay, will create conditions favourable for thunderstorms over the entire state,” said a Met official.
The southerly winds from the Bay are dominant in Bengal now. “Despite the weakening of a cyclonic circulation over Bangladesh, the moisture incursion is still strong,” he said
The Met bulletin has warned people against taking shelter under a tree or an electric pole during a storm. It also advised people against staying in an open area.
Lightning has caused many deaths in Bengal over the past few years.
Thirty-two people died in Bengal on account of lightning strikes in June 2021, of which 27 deaths had been recorded on a single day — June 7.
Bengal recorded the highest number of lightning strikes from cloud to ground per square kilometre in India in 2020, according to the 2020 South Asia Lightning Report.
On January 22 last year, a woman and her son got burn injuries when a thunderbolt hit their house on the ground floor of a three-storey building in a residential area in Bansdroni on Saturday morning.
Several trees were uprooted during Thursday’s thunderstorm in Kolkata. A repeat is not ruled out in the days to come.
Following the Met alert, the directorate of school education issued a notice to the school inspectors in the districts, to do the needful “for making the schools available.. for use as flood shelters during the natural calamities, if required”.
The city received the sharpest thunderstorm so far this season on Thursday evening.
The rain dragged the mercury down. The maximum temperature was 34.2 degrees, a notch below normal. But the relief was offset by the soaring levels of humidity.
The minimum relative humidity, a marker of the moisture content in the atmosphere during the driest part of the day, was 57 per cent.
“For the better part of the day, the humidity level was above 60 per cent. As a result, people sweated profusely,” said a Met official.
“The mercury may rise slightly in Kolkata on Sunday but will fall on Monday,” he added.
The middle of March to the end of May is usually the thunderstorm season in Kolkata.
The city’s quota is around a dozen in this period. But so far this year, there have only been a couple.
“The next few days should tilt the scales,” the Met official said.