The monsoon trough is now the closest to Calcutta that it has been this monsoon, prompting the Met office to forecast a rainy week ahead.

“The monsoon trough at mean sea level now passes through Shri Ganganagar (Rajasthan), Jaipur (Rajasthan), Gwalio (Madhya Pradesh), Sidhi (Madhya Pradesh), Ranchi (Jharkhand), Canning (Bengal) and thence east-southeastwards to Northeast Bay of Bengal,” said a Met report.

Canning in South 24-Parganas is less than 60km from the heart of Calcutta.

“The monsoon trough is now the closest to Calcutta that it has been this season,” said a Met official.

The monsoon trough is an imaginary line connecting various low-pressure points from west to east.

The sky over the city remained overcast on Thursday. Spells of drizzle continued throughout the day.

“A cyclonic circulation lies over Gangetic West Bengal and adjoining Bangladesh and extends up to 7.6km above mean sea level tilting southwards with height,” said Somenath Dutta, head of IMD, Calcutta.

“There is a possibility that the system descends and takes the form of a low-pressure area,” Dutta said.

According to the forecast, on Friday and Saturday, all districts of south Bengal are expected to get widespread rainfall.

All districts of Bengal are expected to get widespread rain between July 29 and
August 1.

The extended range forecast issued by the IMD predicted above-average rain in almost entire south Bengal till August 1.