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Pressure shift may spare city weekend deluge

The mass of cloud that brought heavy rainfall to Calcutta over the past week is inching towards Bihar and its course over the next two days would determine how Calcutta would spend its weekend.

Satellite pictures on Friday evening showed thick clouds to the east and west of Calcutta following a west-ward drift of the low-pressure area that was responsible for the downpours in and around the city between Monday night and Thursday.

“As the weather system is shifting slowly, we expect some rain in Gangetic Bengal on Saturday as well, interspersed with sunny phases. The sky is likely to clear a bit more on Sunday,” said Gokul Chandra Debnath, the director of the India Meteorological Department, Calcutta.

“There is no possibility of heavy rainfall in Calcutta over the weekend. There can, however, be a light drizzle in some parts of the city,” he added.

The wind charts show that the flow of the south-westerly monsoon is strong at the moment — which means it is drawing in loads of moisture from the Bay of Bengal.

With the low-pressure area shifting towards north, the winds are converging more towards Bihar and the northern districts of Bengal.

The atmospheric pressure of a low-pressure area is less than its surroundings. So it pulls winds, in this case air rich in water vapour, from the Bay, leading to the formation of clouds.

From Sunday such clouds would be formed to the north and north-west of the city, which is why heavy rainfall is expected in the north Bengal districts and Bihar, Debnath said.

Calcutta wouldn’t be entirely dry through the weekend as one or two spells of drizzles are expected, especially on Saturday.

“I am tired of the downpours. Waterlogging makes travelling a nightmare in Calcutta. For outdoor activities, an overcast sky is fun but not rain,” said Sonal Singh, a resident of Ekdalia.

If the Met office’s prediction turns out to be correct, the weekend weather will be like what Sonal has been asking for.

On Friday, there was a constant pitter-patter in Calcutta since morning. With the sun remaining behind the clouds, the mercury took a plunge.

The maximum temperature dropped to 27.9 degrees Celsius, the coolest daytime temperature experienced in Calcutta since May 27, when Calcutta recorded a maximum of 27 degrees in the middle of another rainy spell.

The Met office feels the maximum temperature will rise to 32 degrees Celsius on Saturday.

With the moisture still flowing in, the relative humidity on Friday stayed high, varying between 95 and 85 per cent. According to the Met office, the relative humidity will come down gradually.

July — traditionally the wettest month in Calcutta — has got off to a flying start in terms of rainfall. The city received 240mm of showers on the first four days of the month, against the July average of 399.9mm.

The monsoon had arrived in the city on June 18, 10 days behind schedule. But the showers over the weekend has helped erase the deficit in most districts of Bengal, including Calcutta.