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Cloud over chill but not for long

The weekend blip in Calcutta’s coolest November in a decade was caused by a depression over the Tamil Nadu coast that could weaken by Monday, clearing the way for the return of the north-westerly wind.

Sunday was cloudy and warm, the minimum temperature of 21.7 degrees Celsius being the highest since November 5.

“A depression down south triggered moisture incursion all along the coastline, including Gangetic West Bengal. The relative humidity in Calcutta immediately shot up and the flow of the cool north-westerly wind was blocked by the cloud cover,” a senior official of the India Meteorological Department, Calcutta, said.

A depression is a strong low-pressure system in which the atmospheric pressure drops lower than in the surrounding areas, drawing winds from there towards itself.

The system that triggered rain and thundershowers in Tamil Nadu and Puducherry on Sunday had developed over the Bay in the middle of last week.

“There is no weather system in the sea close to Calcutta as of now. So relative humidity is expected to stay in check. Fog isn’t expected in the next few days either,” the Met official said.

The minimum temperature had dropped below 18 degrees Celsius by Tuesday and touched the season’s low of 17.3 degrees on Thursday before going up as the depression approached land.

By Saturday, the minimum reading had increased to 19.2 degrees. On Sunday, it was 20.6 degrees Celsius, two notches above normal for this time of the year.

The forecast is for the minimum to get back to 19 degrees Celsius by Monday and 17 degrees on Tuesday.

The first fortnight of November was the coolest in 10 years, making winter-loving Calcuttans rejoice at the prospect of an early start to the season of chill.

“On Sunday, I took a look at the cloudy sky and thought it might rain, in which case the weather would have been colder. Sadly, the chill seems to have gone away,” said Aparna Roy Chowdhury, a 32-year-old homemaker from Cornfield Road.

The regional Met office in Alipore said rain was unlikely in the city because of its distance from the southern coast, where the depression made landfall.

Calcutta gets 30.7mm of rainfall in November on an average, most of it in the first half of the month. This calculation is based on 30-year data, starting 1971.

While October was rainy this year, November hasn’t seen even a drizzle.

While the minimum temperature increased along with relative humidity, the cloudy sky on Sunday brought the maximum reading down by almost three degrees, from 31.3 on Saturday to 28.4 degrees Celsius.

It is tipped to return to 30 degrees by Tuesday.