A low-pressure area over south Bengal intensified into a depression on Monday, triggering rain across south Bengal.

Calcutta spent another sunless day that saw persistent rain.

Tuesday is also likely to remain overcast and rainy, the sky is expected to get clearer from Wednesday, said a Met official.

“The well-marked low-pressure area over southeast Gangetic Bengal and adjoining Bangladesh concentrated into a depression over the region. On Monday afternoon, it was positioned around 70km from Calcutta and 100km from Burdwan. The system was northeast of Calcutta and was likely to move in a west-northwest direction across Gangetic Bengal,” said a Met official.

The system is unlikely to gain much more steam because it is on land and facing a lot of resistance in the form of buildings, trees and poles, said the official.

The official forecast for south Bengal is “light to moderate rainfall at most places”.

Most Calcuttans woke up to rain on Monday.

Children went to school clad in raincoats. Crowded platforms of suburban railway stations had waves of umbrellas surging forward at coaches of local trains.

Between 5.30pm on Sunday and 5.30pm on Monday, the Met office recorded around 10mm of rain in Alipore. In a Monday morning bulletin, the Met office had warned that Calcutta would end up recording heavy rain by Tuesday morning.

The showers cooled the city. Saturday morning was hot and humid until a cyclonic circulation — the precursor to the depression — over south Bengal led to multiple sharp spells of rain.

The Met office on Monday recorded a maximum of 28.4 degrees in Alipore, down by more than four degrees from what is normal for mid-July.

The Met bulletin predicted “light to moderate rain/thundershower in most places” in south Bengal on Tuesday. In some places, the showers will be accompanied by light gusts of wind.

Heavy rainfall (7-11cm) is expected in Purulia, Bankura, East and West Burdwan, Birbhum and Murshidabad.

In north Bengal, light to moderate rain/thundershower is expected in “many places”. Some areas in Darjeeling, Kalimpong, Jalpaiguri, Cooch Behar and Alipurduar may end up getting heavy rain, according to the forecast.

The run-up to the monsoon had been rainy this year. Almost a month into its arrival in south Bengal, the monsoon has so far recorded surplus rain in south Bengal, according to the Met office.

June and July so far have seen at least five weather systems over south Bengal, including the one active now.

“It is about normal. The entire monsoon season sees around 10 to 12 systems,” said a Met official.