Winter has hit town more than a fortnight ahead of time with the hottest first half of November in five decades making way for what could be the coolest second half of November in a decade.

“We have analysed the data and concluded that Sunday marks the onset of winter in Calcutta,” said Gokul Chandra Debnath, the director of the Regional Meteorological Centre at Alipore.

Sunday’s minimum temperature of 15.2 degrees Celsius was two degrees below normal.

The last time winter had set in more than a fortnight earlier than usual was in 1999. The official record for that year is November 16, when the mercury dipped to 14.3 degrees Celsius, three notches below normal.

In the past five years, the only time winter arrived in November was in 2005 (see box). The date in the records was November 26, when the minimum temperature was 16.8 degrees Celsius.

The weather anomalies through the year — a premature monsoon dragged in by Cyclone Aila; three heat wave-like spells in April, May and June; two record-shattering warm phases in August and November; and now an early winter — are seen as the most erratic in the city’s Met history.

So does the weather hold any more surprises like a longer winter or the coldest one yet?

“Winter’s early arrival does not mean that it will stay longer. In fact, it could leave earlier than usual (around February 20 in a normal year),” said O.P. Sharma, the chief meteorologist in an independent Met agency.

But for Calcuttans longing for winter after a sultry November that hardly mattered on Sunday. The moisture-laden winds from the Mediterranean Sea — called “western disturbance” — and the free play of Northwesterlies over south Bengal resulted in the party season of the year officially arriving in the city.

“The nip in the air was prominent, and it felt like winter even when the sun was out at 11am. I love this season, though going to work at 8am in winter is such a pain. My warm clothes have just come home from the dry cleaners,” smiled bank employee Mansi Sharma, 26.

Monday will be “a bright day with clear blue skies and a further drop in temperatures”, according to the weatherman.

Not that Calcutta needs prodding to bring out the woollens. Stores selling winter wear, especially those in New Market, were teeming with customers throughout Sunday.

Jagbir Singh, the director of the Noida-based National Centre for Medium Range Weather Forecasting, said temperatures had dipped drastically over the weekend at most places south of the sub-Himalayan belt and “Calcutta is no exception”.