The Telegraph
Wednesday , December 18 , 2013
CIMA Gallary

Bay brakes on chill run

A high-pressure belt developing over the Bay of Bengal has threatened to arrest mercury’s slide in Calcutta after cold winds from the north kept the minimum at 13-14 degrees Celsius over the past few days.

The minimum temperature has been dipping since Saturday’s 14.7 degrees Celsius — 14 on Sunday, 13.6 on Monday and 13.3 on Tuesday. That made Tuesday the second coldest December 17 for 10 years, behind 12.2 degrees Celsius in 2011. (See chart)

Met records show that between December 11 and 17, the average minimum has been 14.5 this year. That’s four degrees lower than last year’s average of 18.4 degrees Celsius during the same period.

The weather office said the minimum would crawl back to the 14-degree mark on Wednesday and keep ascending gradually for the next two-three days because of the high-pressure zone over the Bay which would block the cold North Wind’s flow.

“The system is forming along the eastern coast. This would lead to moisture incursion into Calcutta and cut the cold winds from the north. Relative humidity and the minimum temperature would rise concurrently,” said Gokul Chandra Debnath, the director of the India Meteorological Department in Calcutta.

In technical terms, the internal atmospheric pressure is greater than the surrounding area in a high-pressure belt, making winds flow outwards.

Winds radiate in a clockwise direction in the northern hemisphere because of low temperature of the landmass along the coast.

Weather scientists say that all these, simply put, prevent the cold wind from blowing into the city.

The forecast says the minimum may go above 14 degrees Celsius after Thursday, depending on how the Bay system behaves.

“Generally, the impact of a high pressure lingers for a few days because it leaves behind quite a lot of moisture in the air. The moisture is enough to raise the temperature but not good enough to bring rain,” a scientist explained.

Calcutta has been bearing the brunt of Bay depressions over the past month — such as cyclones Helen, Lehar and Madi delaying the cold it had expected.