A cloud cover and a hint of cold balanced out a Celsius spike on Sunday when the minimum temperature rose six degrees above normal, aided by a new wind formation that stuffed the air with moisture and obstructed the North Wind.

The weather office said that the air would be heavy with water vapour at least till Tuesday, after which the mercury would start its descent. The minimum temperature would remain in the range of 19 to 21 degrees Celsius over the next couple of days before touching 18 degrees on Thursday, which would still be a couple of notches higher than normal for this time of the year.

The minimum temperature on Sunday was 21.6 degrees Celsius while the normal reading in the first week of December is around 16 degrees Celsius. On Saturday, the corresponding reading was 20.5 degrees Celsius, five rungs above normal.

Meteorologists said the minimum temperature was on its way down since the influence of a Western Disturbance passed at the end of last week, only for the process of cooling to be thwarted by a cyclonic circulation over Bangladesh and adjoining south Bengal.

"The cyclonic circulation will clear in the next two to three days, although that will not bring about an immediate drop in temperature because the moisture accumulated in the air would take time to disperse," said Gokul Chandra Debnath, deputy director-general of the India Meteorological Department (IMD), Calcutta.

A cyclonic circulation has internal pressure lower than its surroundings, because of which it draws air. In this case, being positioned near the Bay of Bengal, the circulation has been drawing air heavy with moisture from sea to land, triggering a rise in relative humidity. This has come in the way of North Wind.

"The North Wind ferries cold to Calcutta and its surroundings. On Sunday, this wind died down and was replaced by a wind blowing from the southeast, or the direction of the Bay of Bengal. Throughout the day, a southerly or south-easterly wind blew across Calcutta at 2-6kmph," said a senior official of the IMD.

The moisture-laden wind coming inland from the sea also caused clouds to form over the Calcutta sky. As a result, the sun's rays were filtered and solar radiation received by the lower atmosphere diminished, causing the maximum temperature to fall from 29.2 degrees Celsius to 27.6, which is normal for this day of the season.

According to AccuWeather.com, RealFeel temperature was around 30 degrees Celsius even when the sun was out in the afternoon.

RealFeel is a measure of the combined effect of heat and humidity on your skin.

Mist has been forecast on Monday and Tuesday because of the presence of additional water vapour in the atmosphere.