March 10: The season's first thunderstorm hit the city this evening, accompanied by intense rain that brought traffic to a crawl.

The weather department said rainfall would continue tomorrow but might lose some intensity on Dol (Sunday) and could dry up on Holi (Monday).

"The three weather systems that caused today's rain are still intact and drawing moisture from the Bay of Bengal, leading to the formation of rain-bearing, cumulonimbus clouds. Under their impact the city would keep receiving rain for a couple of days," a weather department official said.

The daily rain over the past few days has left students sitting for their board exams anxious.

Several students appearing for the ICSE exams, which started today, said they were worried whether they would be able to reach the exam venues in time if it rained in the morning. Their fear, however, did not come true as the morning was dry.

Several schools said they had made arrangements so examinees were not inconvenienced even if it rained.

"We had asked our guards to stand at the gate with towels and umbrellas. Had it rained the guards would have escorted the children to the school building with umbrellas," said Richard Gasper, the principal and secretary of St. Augustine's Day School.

"All students have been advised to be careful and take necessary precautions so they do not get drenched," said Terence Ireland, the principal of St. James' School.

The Calcutta sky took turns to be sunny and cloudy since morning and the clouds started building up in the evening.

The rain started a little after 6pm and continued for an hour, while the storm hit the city around 6.30. The weather office recorded a maximum wind speed of 56kmph - at 6.40pm - which sustained for three minutes.

"The clouds came over the city from a north-westerly direction. A cyclonic circulation over north Chhattisgarh and an anti-cyclonic circulation over the Bay of Bengal triggered a strong flow of moisture from the sea into the air over the land," said Sanjib Bandyopadhyay, deputy director general, India Meteorological Department, Calcutta.

The cyclonic circulation, which extended up to 2.1km from the surface, was quite strong, meteorologists said.

Apart from the cyclonic circulation and the anti-cyclonic flow, the third factor that led to the formation of rain-bearing clouds was a trough of low pressure, which stretched from west Uttar Pradesh to Assam.

"The thunderclouds formed over the western districts of south Bengal in the afternoon and moved towards the city," a weather department official said.

The civic body said the city received an average rainfall of 25mm in the evening. The downpour, coinciding with the evening rush, resulted in traffic snarls across the city.

The worst-hit pockets included Baguiati, Shyambazar, Brabourne Road, Strand Road, Esplanade, Park Street, Camac Street and Gariahat.

Ankur Jaiswal, a trader in Burrabazar, said it took him around an hour to reach his home in Howrah by bus, against the average commute time of half an hour.

In the New Market area, the pavements were packed with people standing under tarpaulin or plastic sheets of stalls to protect themselves from rain.

Taxi drivers refused people at will. Rajarshi Deb, a Golf Green resident, had come to a shoe store on Lindsay Street. He spotted a yellow taxi and went running after it, only to be refused.

Another asked for Rs 100 plus the normal fare. "I was drenched. I was forced to pay the extra money and take that cab," he said.

App cabs had a field day, too, with surge pricing clocking thrice the normal fares.

Some stretches of Park Street, Camac Street and JL Nehru Road went under water.

The rain disrupted the first day of Outlawed, a three-day annual cultural fest of The West Bengal National University of Juridical Sciences, being held in association with t2. Chords of Fusion, the singing competition, which was scheduled for 7pm on Friday, had to be cancelled and a performance by Delhi-based band The Local Train, which was to be held in the open, was shifted to the auditorium on the campus.