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Nippy North Wind revives winter

Tuesday: 18.3

Wednesday: 15.6

Thursday: 13.3

Friday forecast: 12

Calcutta has become colder by five degrees Celsius in two days.

Maya Bhowmick felt the nip in the North Wind the moment she stepped onto the balcony of her 23rd floor residence at South City and immediately rushed back in for her shawl. Sushanta Sahu felt it while walking by the Dhakuria lakes.

The number of elderly people taking a morning walk by the lakes too dropped suddenly on Thursday. And just as Calcuttans complain when winter isn’t cold enough, many complained out of habit that it was “very cold”.

Winter is already severe in north India and the weather office says the city will get colder over the next two days. “A high-pressure belt along the eastern coast last week had caused a lot of moisture incursion towards land, resulting in the Celsius rising in Calcutta and its surroundings. It took time for that water vapour to be blown away by the northerly winds. Now the chill is being felt,” a weather scientist said.

The normal minimum temperature for this time of the year is 14 degrees Celsius. The gusty northerly wind ensured that the reading for Wednesday was a degree below normal. The forecast is for the minimum temperature to slump by another degree on Friday and remain there, if not drop further, over the weekend.

On Thursday, the minimum temperature fell by 2.3 degrees Celsius to reach 13.3 from 15.6 on Wednesday, continuing the slide that had started the day before. Wednesday had seen a 2.7-degree fall from 18.3 on Tuesday.

The maximum temperature too stayed low at 23.1 degrees Celsius on Thursday.

Snowfall in Jammu and Kashmir has resulted in cold-wave conditions in the north — when the minimum temperature there is five degrees below normal in winter — and that has had a bearing on the Calcutta weather.

“The flow of northerly and northwesterly winds primarily brings chill to the city and its adjoining areas. So if north India feels the chill, Calcutta’s winter picks up too,” a weather scientist said.

On Thursday, the lowest minimum temperature in the plains was 0.9 degrees Celsius, recorded at Churu in Rajasthan.

What sometimes plays spoilsport for Calcutta despite north India experiencing the chill is the growth of pressure systems over the Bay of Bengal that fill the city’s air with excess moisture, thereby impeding the flow of the north wind.

Cyclone Madi had denied Calcutta the sub-16 Celsius hat-trick that would have signalled the advent of winter within the second week of December. November had also seen two cyclonic circulations in south Bay of Bengal affect Calcutta’s transition to winter.

Although no such system exists at the moment, the high-pressure belt on the eastern coast along the Bay of Bengal had resulted in a rise in temperatures after the minimum dropped to 13.3 degrees Celsius on December 17.

As the wind system blew moisture from the sea away from itself due to the high atmospheric pressure within it in comparison to its surroundings, places like Calcutta near the coast also saw relative humidity rise.

“It is because of this system that Calcutta had a warm phase where the minimum stayed between 16 and 19 degrees Celsius. After the system became weak around Christmas, the moisture content in the city air diminished and the Celsius started falling again. The strength of the North Wind added to the chill,” the weather scientist said.

Christmas and Boxing Day this year don’t rank among the coldest in the city, though.

The minimum temperature on Christmas was higher compared to that on the same day in the past 10 years.

There was an improvement in the ranking of the Boxing Day minimum (see chart), but Thursday’s minimum reading was the highest for this day in the last five years.