Clouds at the rear of a Bay system brought rain to the city.

The Met office recorded around 50mm of rain between 5.30pm on Sunday and 5.30pm on Monday. A bulk of the rain happened in the early hours of Monday.

Heavy rain was in store for the city, courtesy of a depression on the Bay of Bengal, the Met office had warned. In Met parlance, that means more than 60mm in 24 hours.

Many Calcuttans thought the system was a damp squib because they were asleep when most of the rain happened.

The system, which had intensified into a depression, hit land in Odisha near Balasore on Sunday afternoon. It moved northwest through north Odisha towards Jharkhand and Chhattisgarh.

“A depression is a large system. Fed by the monsoon currents, numerous circular bands of cloud are part of the system. The outer bands in the tail of the system brought rain to Calcutta and neighbouring regions,” said a Met official in Alipore.

On Monday morning, the system was still a depression over south Jharkhand, 70km south-southwest of Ranchi.

Districts like Birbhum and Purulia got heavy rain on Monday. Calcutta remained mostly cloudy, but the rain was minimal.

The maximum temperature in Calcutta dropped to 29° Celsius, close to four notches below normal.

The sky will be sunny and cloudy in phases from Tuesday. Light rain is expected on Tuesday and Wednesday.

“Thunderstorms are not ruled out,” said a Met official.

But the intensity and spread of the rain in south Bengal will gradually decrease, the official added..

Alert for north Bengal

The seasonal trough is tipped to rise again and reach the foothills of the Himalayas. As a result, north Bengal is bracing for yet another spell of heavy rain. The Met office has issued a red alert for north Bengal.

“The wind pattern will be such that moisture from the Bay of Bengal as well as the Arabian Sea would converge in north Bengal,” said a Met official.

Heavy to very heavy rain is likely in Darjeeling and Kalimpong. Jalpaiguri, Coochbehar, Alipurduar districts may get “extremely heavy rain” (more than 200mm in 24 hours), the Met predicts.