A cyclonic circulation over Bangladesh triggered a sharp spell of showers in Calcutta on Monday afternoon and was likely to cause more rain on Tuesday, said Met officials.

There is a possibility of another similar spell in Calcutta before Wednesday morning, said a Met official. The intensity of the showers will dip from Wednesday, according to the forecast.

Between 8.30am and 8.30pm on Monday, the Met office recorded around 45mm of rain in Alipore (Calcutta). More than 60mm in 24 hours qualifies as heavy rain.

The showers offered relief from the soaring humidity that prevailed in the morning, but flooded several roads and crippled traffic across the city on the first working day of the week.

“An upper air cyclonic circulation lies over north Bangladesh and the neighbourhood. A trough extends from north Bihar to Manipur across the above cyclonic circulation. The monsoon trough passes through Purulia and then east-southeastward into the northeast Bay of Bengal,” said a Met report.

Murshidabad, Nadia and North and South 24-Parganas, districts near Bangladesh, received sharp spells because of the circulation. South 24-Parganas, Howrah, Hooghly, West Midnapore, West Burdwan and Bankura districts are expected to get heavy rain on Tuesday.

A Met official said another strong spell of rain was not ruled out in Calcutta. “The intensity of the rain will dip from Wednesday,” he said.

Before the showers, Calcuttans were tormented by extremely sweaty conditions. At 30 degrees, the maximum temperature was two notches below normal.

But the minimum relative humidity — the moisture content in the atmosphere during the driest part of the day — was over 80 per cent.

The sky started changing colours as the day progressed. By 2pm, dark clouds portended a strong spell of rain. The showers started soon and picked up steam.

Around 3pm, the rain was almost blinding. Several students on their way back from school got drenched.

By early evening, stretches of Diamond Harbour Road, Remount Road and Theatre Road had ankle-deep water.

Traffic crawled across the city. Park Street, Camac Street, Theatre Road and AJC Bose Road were particularly affected.

Monsoon rain in lower Gangetic Bengal is dependent on low-pressure systems over the northern parts of the Bay of Bengal. There have been successive weather systems this year to ensure consistent rain in south Bengal.

July, among the rainiest months for Calcutta, usually gets around 345mm of rain.

This year, it has already seen more than 520mm in Alipore (Calcutta), according to Met records. It translates to a surplus of over 50 per cent.