Most Calcuttans sweated under their winterwear and some even switched on fans on Wednesday, wondering if this was one of the most uncomfortable winter days ever.

It was. With maximum humidity at 100 per cent and the discomfort index touching 61 degrees Celsius, six notches above normal, Wednesday was the hottest December 16 this decade (see chart). The maximum temperature soared to 28.9 degrees Celsius, two degrees above normal and the minimum temperature too was a couple of notches above normal, at 16.4 degrees Celsius.

“A lot of moisture is still coming into the atmosphere over south Bengal from the Bay as a result of a low-pressure area. The moisture is trapping heat and increasing humidity, thus pushing up the discomfort factor,” Gokul Chandra Debnath, the director of the Regional Meteorological Centre at Alipore, told Metro.

The low-pressure area in question is the residue of Cyclone Ward, now lying over the Gulf of Mannar and adjoining Tamil Nadu.

According to meteorologists, the moist and warmer wind from the Bay of Bengal is blocking cool, dry northwesterlies, a key factor for lower temperatures in the city and its neighbourhood this time of the year. Moreover, western disturbances this winter have not only been weak, but few and far between.

Temperatures and humidity have stayed above normal since Friday because of the formation of Cyclone Ward. But the cyclone’s steady dissipation didn’t result in greater comfort for the city.

“These conditions are likely to persist for at least two more days. A drop in humidity would result in a slide in temperatures as well,” said the chief meteorologist of a private agency.

According to a senior scientist at the National Centre for Medium Range Weather Forecasting in Noida, western disturbances are likely to intensify after Monday, by when the low-pressure area should cease to exist. Reduced humidity would clear the path for the entry of northwesterlies over south Bengal, which should lead to a dip in the mercury.