The monsoon trough that was playing truant with the city is now passing through it and the result was rain throughout Tuesday night and another sharp spell on Wednesday morning.
A trough of low pressure that was south of Calcutta climbed north on Tuesday night, propelling the rain-bearing clouds towards the city, the Met office said.
The trough is tipped to rise further north. The Met office has issued an “enhanced rain” alert for north Bengal till July 2.
South Bengal, including Calcutta, will see the sky clearing up over the next 48 hours, the Met office said.
The rain, the season's heaviest so far, became more intense as the night progressed. A brief pause in the morning was broken by another sharp spell that began around 7am. The showers subsided by 9am.
The rest of the day saw a drizzle or two. But the conditions remained gloomy.
Between 2am and 9am, Ballygunge received close to 90mm of rain, according to data from the drainage pumping stations of the Calcutta Municipal Corporation. Some parts around Garia received over 130mm around the same time. In Met parlance, 60mm of rain in 24 hours qualifies as heavy.
Parts of EM Bypass near Dhapa got around 48mm, Topsia got 56mm and Behala got 40mm around the same time. In the north, Maniktala received 30mm and Ultadanga 35mm, said an official in the drainage department of the civic body.
The Met office recorded around 41mm of rain in Alipore between 8.30pm on Tuesday and 8.30pm on Wednesday.
“A trough of low pressure extends from northwest Rajasthan to the northeast Bay of Bengal. It is passing directly through Gangetic Bengal, including Calcutta. Till yesterday, the trough was south of coastal Bengal and ended in the northwest Bay, which is closer to Odisha and Andhra coasts,” said G.K. Das, director, India Meteorological Department, Calcutta.
“As the trough moved north, it carried the strong clouds that were over the Bay of Bengal. The clouds triggered the rain in Calcutta and adjoining areas,” he said.
Parts of the Sagar island, around 100km from Calcutta, received over 100mm of rain through the night, said Met officials.
“Calcutta and other coastal areas in south Bengal are expected to get one or two spells of rain on Thursday. But the sky is expected to start clearing from Thursday evening or Friday,” said Das.
The rain and clouds dragged the maximum temperature down to 28.3 degrees, five notches below normal, on Wednesday.“The Celsius is likely to rise gradually from Friday. By the weekend, the maximum temperature is tipped to be around 33 degrees,” said an official.