Kolkata: Dusk descended on the city in the afternoon ascloud columns, as high as 8-12 km, engulfed the skies on Thursday. While areas, such as Salt Lake, New Town, Lake Town, Dum Dum and Howrah, were pounded by heavy rain, accompanied by thunder and lightning, the intensity was slightly less in southern and central Kolkata.According to the Met office, the intensity of the rain is likely to reduce but thunderstorms may hit the city on Friday, the day Vishwakarma Puja will be celebrated.The steady downpour for around one-and-a-half hours on Thursday afternoon flooded parts of Salt Lake, including Sector V. “The main reason behind the Thursday thunderstorm was an upper air trough from Sikkim to Odisha across Gangetic West Bengal. The heating, abundant moisture and the diverse wind pattern in different layers played together to pull off intense cloud formation,” said H R Biswas, head at Regional Meteorological Centre (RMC) Kolkata. Dense and high clouds, created by this system, encircled the skies, plunging parts of Kolkata into darkness as early as 1.30 pm. Thunder, lightning and downpour followed, with the intensity of the rain peaking around 2 pm.Salt Lake recorded more than 50 mm of rainfall.In meteorological parlance, a trough is an elongated stretch of low atmospheric pressure. If low-pressure systems are like broad bowls, where air collects, a trough is like an elongated, narrow valley between hills of high pressure. This trough acts as a powerful atmospheric lifting mechanism, forcing warm, moist air upward into an unstable environment to cause intense a thunderstorm. “We can expect thunderstorms in Kolkata and other parts of south Bengal on Friday, too, but the intensity is likely to be less in the city,” added Biswas.On the possibility of a cyclonic storm, which is being discussed on the social media, the RMC Kolkata head clarified that there was indeed an upper air cyclonic circulation over north Thailand but it was not certain if this system would intensify into a cyclone. “This system is likely to emerge over north of the Andaman Sea and propel the formation of a low pressure area by Saturday. There is an indication of the system to further intensify and move towards south Odisha-north Andhra Pradesh. By Sunday or Monday, we will get a clearer picture of whether this system could intensify into a cyclone or not. For now, we see no major weather system, apart for the present condition, impacting the rain pattern here,” added Biswas.While it rained in Kolkata on 10 out of 17 days of Sept so far, the dry spell the past three days had pushed up the maximum temperature above the normal mark.
