Most Calcuttans woke up to heavy rain on Tuesday, accompanied by the occasional gust of wind. By daybreak, some of the city’s busiest roads — BB Ganguly Street, Central Avenue, Camac Street, Park Street, Chowringhee and Prince Anwar Shah Road — were under water.

Attendance was thin in schools as many parents did not send their children. In some schools, attendance was as low as 25 per cent. Several teachers could not make it to school either.

A low-pressure area that stayed much longer over coastal south Bengal than expected triggered the heavy overnight rain in the city and adjoining districts. Strong monsoon currents teamed up with the system to cause the downpour.

In Calcutta, widespread rain started around midnight. The intensity peaked between 4am and 8.30am on Tuesday, a Met official said.

The spread and intensity of the rain reduced from the afternoon, but the day remained sunless and gloomy.

The Met office has predicted that conditions will improve from Wednesday. It is still likely to be wet but not as rainy as Tuesday, according to the forecast.

Between 5.30pm on Monday and 5.30pm on Tuesday, Alipore received around 90mm of rain. Of the total volume, only around 11mm was between 8.30am and 5.30pm on Tuesday, according to the Met readings.

Dum Dum got close to 100mm between Monday evening and Tuesday evening, most of it between 5am and 8.30am.

More than 60mm of rain in 24 hours qualifies as heavy.

The low-pressure area, which took shape over Gangetic Bengal on Sunday, was supposed to move slowly west-northwest towards Jharkhand. But it hardly moved, said a Met official.

“Most of south Bengal got rain. It was most intense in Calcutta and the adjoining districts of South and North 24-Parganas, Howrah and Hooghly,” said H. R. Biswas, head of the weather section at the Regional Meteorological Centre in Alipore.

The low-pressure area was over “Gangetic West Bengal and the neighbourhood” at 8.30am on Tuesday, said a Met bulletin. Exactly 24 hours earlier, it was over “south-west Gangetic Bengal”, which means it was almost stationary, said the Met official.

“It is likely to move slowly west-northwestwards across Jharkhand and north Chhattisgarh by Thursday,” said the bulletin.

The monsoon trough now passes through Bhatinda (Punjab), Rohtak (Haryana), Kanpur (Uttar Pradesh), Daltonganj (Jharkhand), before moving through the centre of the low-pressure over south Bengal into the northeast Bay of Bengal, the bulletin said.

“The southwest monsoon has been vigorous over Gangetic Bengal,” it said.

As the low-pressure area moves towards Jharkhand, heavy rain is expected in
West Burdwan, Purulia,
Jhargram and Bankura districts on Wednesday.

“Calcutta is likely to get more rain. But the spread and intensity of the showers are likely to dip and the interval between two spells is likely to go up,” said a Met official.

The run-up to the monsoon has also been rainy this year. The monsoon has been generous so far. Continuous rain and already-brimming city canals led to the waterlogging, the civic body said.

The pumping stations of the civic body recorded 96mm of rain in Maniktala between midnight and noon on Tuesday. Palmer Bridge received 97mm, Ultadanga 88mm, Thanthania 93mm, Ballygunge 78mm and Behala 70mm.