The monsoon is on course to set foot in Calcutta between Monday and Wednesday, the Met office said.

Sunday began on a rainy note. The morning was overcast, but the sky cleared partially as the day progressed.

A Met bulletin issued on Sunday warned of an increase in rainfall activity across the state.

“Latest meteorological analysis indicates that the conditions are favourable for further advancement of the southwest monsoon over some more parts of Odisha during the next 24 hours; over some parts of Bengal, Jharkhand and Bihar during the subsequent three days,” it said.

The monsoon’s usual arrival date in north Bengal is June 5. For south Bengal, the date is June 10. This year, the southwest monsoon made a premature entry into north Bengal on May 29. But south Bengal is still waiting for it.

“The monsoon currents are active on the Bay of Bengal. Multiple systems are at play. The monsoon is expected to arrive in south Bengal between June 16 and 18,” said a Met official in Calcutta.

The monsoon makes a meek arrival if the monsoon currents are weak on the Bay. A strong system, accompanied by active monsoon currents on the Bay, often propels the monsoon into the land with formidable rainfall.

The Met bulletin issued on Sunday said: “The cyclonic circulation over south Bangladesh and adjoining north Bay of Bengal now lies over northwest Bay of Bengal and the neighbourhood between 3.1 and 7.6km above mean sea level tilting southwestwards with height. The cyclonic circulation over westcentral Bay of Bengal off north Coastal Andhra Pradesh coast at 5.8km above mean sea level has merged with the above cyclonic circulation.”

“Yesterday’s trough now runs from East Madhya Pradesh to Bangladesh across Chhattisgarh, Jharkhand and Gangetic West Bengal and extends up to 1.5km above mean sea level, tilting southwestwards with height,” the bulletin said.

“In view of the above and strong moisture incursion from the Bay of Bengal, enhanced rainfall activity with isolated heavy to very heavy rainfall is very likely in some districts of Bengal,” the bulletin said.

The rain is likely to be uniform and widespread between Monday and Wednesday. North and South 24-Parganas and East and West Midnapore are likely to be among the wettest places in south Bengal. Calcutta is also likely to get at least one spell of heavy rain between Tuesday and Wednesday, Met officials said. Several areas in north Bengal are also likely to get heavy rain.

“The next two weeks are going to be rainy across Bengal. Another system is expected to take shape on the Bay of Bengal next week, said Met officials.