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Chilly spell back, wind block ahead

The cold made a comeback in Calcutta on Tuesday courtesy a strong northerly wind but a cyclonic circulation brewing over central India could cut short the chill. Again.

Weather satellites have picked up signals of the circulation moving east. It will start drawing moisture from the Bay of Bengal once it’s within striking distance of Calcutta and could nick the cold North Wind’s flow, a phenomenon that’s become all too familiar this winter.

The mercury plunged overnight because of the brisk northerly wind and dense fog that hung loose over the city till late in the morning. The minimum fell by 2.3 degrees Celsius from Monday to reach 13.5, a rung below normal, while the maximum slipped by 1.7 degrees to settle at 22.3.

If Tuesday’s maximum was two notches below normal, the weather office said it could dip further on Wednesday.

“We expect the minimum temperature in Calcutta to drop to 13 degrees Celsius and stay in that range on Thursday. But we expect a rise in temperature from Friday because a cyclonic circulation, currently hovering over central India, would push up the relative humidity in the city and its surrounding areas,” said G.K. Das, a meteorologist at the Regional Met Office in Alipore.

A similar circulation passed the region last Saturday, making the minimum temperature jump to 16.4 degrees Celsius. Weather scientists said these systems were induced by Western Disturbances over northern India.

The minimum might have fluctuated but day temperatures have been low in the city from the beginning of the year. The last time the maximum crossed the normal mark was on January 2.

Relative humidity was high on Tuesday morning — 90 per cent at 8.30am — as overcast skies spawned dense fog across the city, especially on open spaces such as the Maidan and the riverfront.

“The Maidan was under a blanket of fog even at 10am and people on the streets were wrapped in woollens. The day stayed cold even after the sun peeked out after noon,” said 27-year-old Rakhi Roy, who crosses the stretch every weekday on the way to her Camac Street office.

Meteorologists warned that foggy conditions would prevail on Wednesday and Thursday as well.

Foggy conditions occur when the air becomes saturated with moisture and the temperature dips below the dew point — the point at which vapour in a volume of humid air condenses into water.

“Fog happens when relative humidity is over 78 per cent and the temperature is close to zero. If the humidity is more, fog can happen at temperatures much more than zero (the temperature was 14.9 degrees Celsius at 8.30am),” said a weather expert.

The fog forced the mercury to stay put in the 16-degree range till 11am. “The cloud cover shielded the earth’s surface from the sun,” the weather expert said.

Dense fog has affected the movement of trains while flight schedules have gone haywire over the past two-three days.

“Visibility sometimes comes down to a few metres in winter. Train drivers are told to maintain a restricted speed to avoid untoward incidents in such conditions. This leads to delays,” said an official of Eastern Railway.