The chilly wind was back in Calcutta on Friday after about 10 days, bringing with it the promise of a three-degree drop in the mercury by Saturday. The cold phase, however, is unlikely to last beyond the weekend.
Friday’s minimum temperature, recorded at dawn, was 15.6 degrees, three notches above normal. But a cool northerly wind started blowing during the day, catching Calcuttans who had stepped out without adequate warm clothes on the wrong foot.
The maximum temperature dropped from 26.6 on Thursday, two notches above normal, to 23.1 on Friday, two degrees below normal.
According to meteorologists, the northerly wind will bring the minimum temperature down to 13 degrees on Saturday. There might be a further fall of a degree on Sunday but after that the wind is likely to be blocked again and the mercury will gradually rise.
“A cyclonic circulation has developed near Rajasthan. This is likely to travel east. Even if the system comes till Bihar or Jharkhand, it will boost moisture flow from the Bay into south Bengal, resulting in a renewed rise in the mercury,” said an official at the India Meteorological Department, Calcutta.
A cyclonic circulation, with an atmospheric pressure lesser than its surroundings, pulls matter towards itself. In this case, it would pull moisture-laden air from the sea towards the land, blocking the chilly wind from the north and pushing up the relative humidity in places close to the coast, such as Calcutta.
The northerly wind was denied a free flow in eastern India for about 10 days because of a high-pressure belt in central India. The rise in the minimum temperature to 15.6 degrees on Friday was because of a cyclonic circulation over and around Bangladesh. These two systems, however, weakened on Friday, leading to a revival of the North Wind.