The sun shone through most of Thursday, but the Met office warned of more rain in the next 48 hours.

The Alipore weather office warned of “fairly widespread rain in Calcutta and the districts of Gangetic Bengal” till Saturday. There is a possibility of heavy showers in isolated pockets, it added.

The upper-air cyclonic circulation (anti-clockwise movement of air), that had formed over Jharkhand on Wednesday, shifted slightly on Thursday and now lay over north Orissa and the adjoining areas of Gangetic Bengal and Jharkhand. In addition, there is a monsoon trough over Gangetic Bengal.

“The cyclonic circulation is sucking in moisture from the Bay of Bengal and the monsoon trough is right over Gangetic Bengal. So, we expect fairly widespread rain during the next two days,” said G.C. Debnath, the director of the weather section at the Regional Meteorological Centre in Alipore.

Met officers explained that there is heavy incursion of moisture into the land from the Bay of Bengal which is already laden with moisture from the recent depression that drowned Calcutta and the south Bengal districts.

“There is so much moisture over Gangetic Bengal that tall columns of thunderclouds have formed over land and widespread rain is expected,” a Met official said.