Calcutta got a feel of summer-like conditions ahead of time on Thursday with the minimum temperature soaring from 9 degrees Celsius eight days ago to 16.6 and peaking at 28.4, the highest it has been since December 11.
Only nine days ago, the maximum reading was 19.3 degrees Celsius, seven notches below normal.
Keeping the Celsius company in the day's summer preview was the maximum relative humidity of 98 per cent, the highest it has been in the last 96 days.
The last time humidity was that high in the city was on October 13.
Thursday was also the first day since December 11 when both the minimum and maximum readings were above normal by more than a degree.
The muggy weather through the day forced many to discard their pullovers and jackets while on the move.
"It got so hot in the afternoon that many of my fellow bus passengers took off their sweaters. It felt more like April and May than January," said trader Diptangshu Mitra, who was headed for Gariahat by bus from Behala Chowrasta around 2pm.
The day temperature is likely to "stabilise" around 28 degrees Celsius in the next two or three days but the minimum will continue its upward march, according to the weather office.
"There is an anti-cyclonic circulation over Jharkhand, Bihar and parts of Odisha. This is causing heavy incursion of moisture, blocking the north wind," a senior official of the India Meteorological Department said.
An anti-cyclonic circulation draws moisture towards itself just like a cyclonic circulation, but the wind moves clockwise. "Moisture incursion is responsible for the high relative humidity and the foggy mornings. The trend will continue on Friday and Saturday," the official said.
The anti-cyclonic circulation is likely to stay active for at least another day. What might bring relief is rain in Jharkhand or north Bengal because of cloud formation triggered by the wind system.
"Rain is not expected anywhere near Calcutta because the clouding has not really happened here. But if it rains in Jharkhand or north Bengal, the moisture in the air in those places will subside and the northern wind that blows the cold into these parts will pick up," a weather scientist said.
There is time yet for another spell of cold in Calcutta, though the intensity is unlikely to be like the sub-10 temperatures recorded at Alipore on January 9 and 10. On January 9, Dum Dum had recorded a minimum of 6.6 degrees Celsius.