Monsoon is set to start retreating from Bengal from Monday, the Met office has said.

Calcutta, and much of south Bengal, have been dry for the past two days after a long and incessant period of rain.

“Conditions are favourable for further withdrawal of southwest monsoon from the remaining parts of Maharashtra, Madhya Pradesh, Uttar Pradesh, and Bihar; entire Jharkhand and Chhattisgarh and some parts of Bengal, Sikkim, Odisha and Telangana during the next 24 hours and from Northeast India during the subsequent two to three days,” said a national bulletin issued by the India Meteorological Department.

Met officials were non-committal on whether the monsoon would be gone from Calcutta by Monday.

Weather scientists generally treat three to four rain-free days as a prerequisite to announcing the withdrawal of the southwest monsoon. A dip in the moisture content in the air is another marker of the end of the monsoon. The third, and most significant, marker is a reversal in the flow of winds.

The close of the monsoon period is indicated by the arrival of winds from northern India.. The winds from the direction of the Bay gradually stop flowing into the city.

Dry northwesterly winds are entering south Bengal, even in the lower atmosphere, said a Met official in Alipore.

The usual date of the withdrawal of monsoon from Calcutta is October 10 to 12.

This monsoon has recorded a considerable surplus of rainfall in Calcutta. This month has already been marked by a prolonged wet spell, featuring two days of substantial rain. A combination of weather systems in the Bay of Bengal and vigorous monsoon currents has led to this surplus. The precipitation in October has mainly taken the form of thunderstorms, triggered by the merging of dry winds from the northeast with moist winds from the Bay.

“An upper-air cyclonic circulation lies over the southwest Bay and the adjoining Tamil Nadu coast. But it does not have any impact in south Bengal,” said the Met official.

The forecast for south Bengal says as much. Dry weather is likely across south Bengal, including Calcutta, for the next few days.

The southwest monsoon begins its withdrawal from Rajasthan. The expected date for this is September 17. This year, the withdrawal process started a bit ahead of schedule. However, it was interrupted by systems over the Bay, which escalated into a deep depression when it made landfall in Odisha on Dashami. The withdrawal process restarted after the system lost strength.