KOLKATA: A nor’wester breezed through Kolkata on Monday evening at a wind speed of 32 km/hr after lashing East and West Midnapore, Howrah, Hoogly, North 24 Parganas and eventually striking South 24 Parganas. It triggered a drizzle across central and south Kolkata. This was the sixth thunderstorm of the season.
Even though it’s steadily getting warmer in Kolkata, it could have been worse. Three squalls and five thunderstorms have struck the city since March, bringing the mercury down at regular intervals after a temperature surge. The number of rainy days, too, have been higher this year than 2017, keeping the summer heat at bay. On Monday, Kolkata recorded a maximum temperature of 35.8°C.
This year, squalls — thunderstorms accompanied by a wind speed of at least 45km/hr that lasts a minute — struck Kolkata on April 1, 7 and 17. The last one turned out to be a devastating one with a peak wind speed of 98km/hr. Between March and April 2017, too, the city had received three squalls. But what has made the difference this time is the regular occurrence of thunderstorms that border on squalls.
“We have had six thunderstorms so far that have had a cooling effect, very similar to that of a squall. In fact, there is a very thin difference between a squall and thunderstorm. So, if the latter keeps happening regularly, the summer heat remains in check,” said
GK Das, director of the
Regional Meteorological Centre (RMC). Last year, the city was lashed by squalls on March 10, 11 and April 19.
The number of rainy days, too, has been higher this time. “We have had nine rainy days so far. It was far less last year. Whenever it rains, the mercury slides and the stifling humidity disappears,” said Das. Only thunderstorms can neutralize the effect of scorching winds blowing into
Gangetic Bengal from central India in summer, said a weather scientist. “A thunderstorm or a squall can pull the mercury down by anything between 2°C and 10°C. This is exactly what has happened this time. Last Tuesday’s squall brought the mercury down by 9°C, which was a big difference. The effect lasted the next day,” he said.
Three factors contribute to a squall or a thunderstorm — moisture incursion from the sea, heating of land in Gangetic Bengal and Jharkhand and cyclonic circulations. All of them have been happening quite regularly this season, pointed out Das. “It is a normal phenomenon, though. In some years, the frequency of the contributing factors go down. So, thunderstorms turn rarer,” said Das.
A 20-year analysis of the city’s weather puts the average April mean temperature (maximum) at 30.2°C. It rises to 30.7°C in May, which is the hottest month of the year. The city receives around a dozen thunderstorms between March and May on an average.
