The past few days have been hot and humid for the city. The dry winds from north India, which bring a hint of cold around this time of the year, are absent.

A system over Bay of Bengal is behind the ordeal for Calcuttans. It is tipped to make the run-up to Kali Puja wet, a Met official said on Tuesday.

The maximum temperature had been two notches above normal on Friday, Saturday and Sunday.

On Monday and Tuesday, it remained a notch above normal. The minimum temperature, too, has been on the higher side. The relative humidity has been hovering in the mid-90s, making Calcuttans sweat more.

After Durga Puja, the moisture content in the air was low and dry northwest winds had just started blowing in. But that was for a brief time and the fluctuations in temperature and humidity levels have caught several Calcuttans off guard and in the grip of fever and respiratory problems.

“A low-pressure area over westcentral and adjoining southwest Bay of Bengal is moving towards Andhra Pradesh and Chhattisgarh. The system is sucking in a lot of moisture from the sea and is tipped to trigger rain and thundershowers in several districts of Bengal between October 23 and 26,” the Met official said.

The western and central districts of Bengal are likely to get more rain under the impact of the system. Calcutta is tipped to get light to moderate rain, he said.

“The moisture incursion from Bay of Bengal is preventing the dry winds from north India from entering the state. A low-pressure area over the Arabian Sea is proving to be another stumbling block for the winds, which herald the onset of winter in Calcutta,” Sanjib Bandyopadhyay, deputy director-general, India Meteorological Department, Calcutta, said.

The moisture in the atmosphere is causing the rise in the mercury, he said.

The monsoon had officially left the city this year on October 14. Weather officials had then spotted wind blowing from north India instead of southwest, the direction of the Bay of Bengal. That means dry winds from north India had started replacing the moisture-laden winds from the Bay of Bengal.

The minimum relative humidity, a measure of moisture in the air during the day, had decreased to less than 50 per cent on three days between October 12 and 15.

“The moisture will be sucked out of the atmosphere after the system passes by, paving the way for the dry northwest winds to enter the city and reduce the temperature,” a weather scientist said.