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Helen takes wind out of winter sails

A satellite image on Friday shows cyclone Helen’s trajectory and the cloud cover over Calcutta

Winter has knocked on the door but Helen and similar systems over the Bay of Bengal have conspired to delay the chill, despite the city recording the nippiest November in a decade during the first half of the month.

Cyclone Helen has pushed up the minimum temperature in Calcutta by nearly two notches by partially restricting the flow of the cold, dry Northerlies and Northwesterlies — the wind systems that determine the city’s chill factor.

Though the cyclone made landfall on the Andhra Pradesh coast on Friday afternoon, the residual impact is expected to affect Calcutta’s weather over the next 24 hours.

An India Meteorological Department official said night and morning temperature would always remain slightly up on the warmer side during overcast conditions in the November-February period. “The cloud cover acts like a blanket, trapping thermal air rising from land and denying entry of cold winds blowing from the Himalayas. Which is why the minimum temperature does not dip.”

The cloud quilt traps moisture as well and Friday’s maximum humidity touched 86 per cent, around 15 per cent higher than normal for this time of the year.

The Helen effect left many Calcuttans feeling hot. “I carried a windcheater to work… given the evening nip of the past few days. Today was different. It was warm. The nip was missing,” said 30-year-old techie Samrat Datta, who drives through the EM Bypass to his Kasba office.

The weather office said the weekend would be partially overcast because of a Helen after-effect and another low-pressure system over Andaman Sea that might intensify into a cyclonic storm.

“Cyclonic storms drastically, but temporarily, alter weather patterns in a vast area around them. Helen, though it stayed hundreds of miles away from the Bengal coast, halted winter’s progress after the first half of this month was the coolest November in a decade,” a Met official said.

“If another cyclone brews over the Bay, it will defer the city’s date with winter by a week or so,” he added.

“The Celsius can dip only if the skies are clear and blue. If there are substantial atmospheric formations over the Bay, they delay the progress of winter,” the official added.

Gokul Chandra Debnath, the director of the Regional Meteorological Centre at Alipore, said the cloud cover would remain for the good part of next week as well but the possibility of rain was remote.

“Calcutta will have to wait till the end of this month for the minimum temperature to dip further. Whether the low-pressure system (over Andaman Sea) evolves into a cyclone or not, it is likely to affect the city’s weather for several days,” he said.

During the weekend, the maximum temperature is likely to stay near the 29-degree mark and the minimum may not go below 18 degrees Celsius.

“The weather will be colder from December 1. Winter usually arrives in the city around December 7 and stays till the third week of February. Calcutta is currently going through a pre-winter transition phase,” a weather scientist said.