A mounted policeman patrols rainswept Chowringhee on the eve of Wednesday’s 24-hour Bengal bandh. The city and the south Bengal districts received widespread rain on Tuesday. The Alipore Met office predicted more rain, including spells of isolated heavy showers, over the next 48 hours. The trough of low pressure that develops during monsoon lay close to Calcutta on Tuesday. There is also a strong cyclonic circulation (anti-clockwise movement of air) over Gangetic Bengal and adjoining Bangladesh. “Monsoon has become active under the influence of the two atmospheric systems,” said G.C. Debnath, the director of the weather section at the Regional Meteorological Centre in Alipore. The cyclonic circulation is likely to intensify in the next 24 hours. On Tuesday, the sky was overcast from dawn. The drizzle intensified in the afternoon. The Met office recorded 21.1 mm of rain till 8.30pm. According to the weatherman, monsoon in Calcutta and its adjoining districts was subdued over the past few days. “The monsoon trough lay over Malda. It shifted towards Calcutta on Monday night. The strong cyclonic circulation over Gangetic Bengal and adjoining Bangladesh led to heavy incursion of moisture from the Bay of Bengal and formation of rain clouds. A fairly strong breeze from the sea helped bring in the moisture,” said a Met official. Picture by Pabitra Das