The Celsius dropped below 13 degrees for the first time in Calcutta this season even as the Christmas spirit soared on Tuesday, the chill in the Yuletide air as much a festive accessory as the Santa caps dotting Park Street in the evening.

Kakoli Sengupta skipped her regular morning walk because of the stiff breeze, which combined with clear skies to drag the temperature down to 12.6 degrees Celsius, a notch below normal for this time of the year.

The weather office has forecast a minimum temperature of 12.5 to 13.5 degrees Celsius over the next two days.

'It was so cold in the morning. I usually go out for my morning walk at 7am but did not feel like dragging myself out of bed till 7.30am today,' said Sengupta, who teaches international relations at Jadavpur University and lives in the Jatin Das Road neighbourhood.

The breeze, which had been blowing at a speed of 7 to 9kmph from the northerly direction in the morning, made the weather feel even colder than the Celsius reading suggested.

According to AccuWeather.com, the temperature was 13 degrees Celsius at 7 in the morning but the breeze made it feel like 12 degrees Celsius on the skin. 'A T-shirt and a sleeveless sweater over it had worked for me until Monday. But the cold, steady breeze on Tuesday morning made this combination inadequate,' said Arun Roye, a 35-year-old out on a walk.

The Met office said there was no weather system in the vicinity to pump in moisture, which is why the northerly and northwesterly winds were blowing freely into south Bengal.

'In some of the south Bengal districts, the temperature has plunged three degrees below normal. This weather is likely to continue for a couple of days at least,' said G.K. Das of the India Meteorological Department, Calcutta.

He said the North Wind might pick up on Christmas Day, adding to the chill.

Since there isn't much moisture in the air, the skies should be clear, as was the case on Tuesday. The absence of clouding allowed the sun to beat down on the city during the day and the lower atmosphere absorbed the radiation, which is why the temperature rose as the day progressed. But the breeze kept blowing till 2pm.

'After that, the direction of the wind shifted to a westerly direction and stayed so till 5pm. That is when some amount of moisture incursion took place,' a Met official said.

Arindam Ganguly, whose job involves being outdoors for long periods, felt the fluctuation in temperature. 'I wore a thick T-shirt under a full-sleeve sweater when I stepped out for work. Around 3pm, I was suddenly sweating,' he said.

Such weather is likely to continue for some time. Some clouding is expected early next week and only then will both the minimum and maximum temperature come down simultaneously, the weather office said.