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Cyclone damper on monsoon hope

The hot and humid spell is likely to continue longer than the Met office’s prediction on Sunday as the monsoon has been delayed further by a day or two.

A cyclonic circulation over the east-central Bay that was driving the long-overdue monsoon towards south Bengal has veered towards Myanmar, slowing down the march of rain.

Meteorologists had said on Sunday that the south-westerly monsoon would reach Calcutta by Tuesday, factoring in the weather phenomenon over the Bay.

The Met office revised its prediction on Monday, saying the onset could be delayed by a day or two.

The monsoon normally reaches Calcutta between June 8 and 10. By June 15, the northern limit of the monsoon usually covers Bihar and touches Uttar Pradesh.

In the west, too, the monsoon has been making slow progress.

“A cyclonic circulation, being a low-pressure zone, draws air towards itself because of an atmospheric pressure that is lower than that of the surroundings. Had the cyclonic circulation over the east-central Bay not veered towards Myanmar, the monsoon would have arrived sooner,” said G.C. Debnath, director, India Meteorological Department. “At the moment, it seems the south-westerly monsoon would not reach Calcutta at least till Wednesday (June 18).”

Till the end of last week a depression over Arabian Sea, which turned into a cyclone for a couple of days, had been holding back the monsoon.

After the depression dissipated, the cyclonic circulation showed up over the Bay of Bengal, raising hopes that the monsoon would finally arrive in the city.

“Since the formation has drifted away, Calcuttans may have to wait a couple of days more for lasting relief from the hot and humid spell. Till the monsoon comes, the city will have to be content with brief respites resulting from the occasional squall or thundershower,” said a weather scientist.

Monsoon winds which blow from the south-west result in heavy moisture incursion into the continental landmass, especially when the flow is strong. “The clouds that form are generally spread over a larger area than the thunderclouds of summer. So, the monsoon rain lasts longer and cools down the weather,” the scientist said.

On Monday, the city’s maximum temperature was 37.1 degrees Celsius, four notches above normal but 1.2 degrees down from Sunday’s maximum. The relative humidity, however, was high enough throughout the evening to torment Calcuttans.

“There is a cyclonic circulation over Bihar, from which a trough of low pressure has come down to Gangetic Bengal. That’s why moisture is entering the lower levels of the atmosphere and making the weather muggy,” said a weather department official.

Cumulonimbus clouds blew towards the city on Monday, in a rerun of what has been happening over the past week, but that hardly brought any relief.