Alipore: A change in the wind flow and rise in the moisture content of the air pushed the city's RealFeel above the 40-degree mark for the first time this season on Tuesday even though the actual temperature was much lower.
RealFeel, devised by weather portal Accuweather.com, is a measure of the effect of the temperature, relative humidity, wind and the angle of the sun on the human skin.
The Alipore weather office recorded a maximum temperature of 35.6 degrees Celsius, two degrees above normal. The RealFeel around that time read 41 degrees Celsius.
"It's unusual for the RealFeel to cross the 40-degree mark in the first fortnight of March," a weather scientist said.
The spike is being attributed to a change in the direction of the wind.
"South-westerly wind from the Bay of Bengal is blowing across the city, replacing dry wind from the north-west. The change has resulted in the city air being loaded with moisture, pushing up the discomfort index and the RealFeel. Around noon, the relative humidity varied between 40 and 50 per cent," the scientist explained.
The wind flow has changed because of the development of a low-pressure trough over Uttar Pradesh.
Later in the afternoon, however, the relative humidity dipped with the direction of wind changing from south-westerly to north-westerly. This happened as the trough shifted from Uttar Pradesh and stretched over east Bihar to Manipur.
"With the low-pressure trough shifting, we expect discomfort levels to come down in the city from Wednesday," said Sanjib Bandyopadhyay, deputy director general, India Meteorological Department, Calcutta.
The average maximum temperatures for the first 13 days of March over the past five years years show that the weather this year has been unusually warmer at the start of summer (see chart).