A deep depression triggered heavy overnight rain in Kolkata while it was moving from Bangladesh towards Jharkhand via south Bengal.
The bulk of the rain came down while the city was asleep. But many Kolkatans were jolted out of their slumber by the clap of thunder late on Tuesday.
Between 10pm on Tuesday and 6am on Wednesday, the Met office recorded a little over 60mm of rain in Alipore. Based on figures obtained from the pumping stations of the civic body, Garia, Behala and Ballygunge got around 90mm of rain in the same period.
In Met parlance, 60mm of rain in 24 hours qualifies as heavy.
The showers came in phases throughout Tuesday but picked up steam at night.
A Met official said the system was closest to Kolkata between 10.30pm and 11.30pm, when it was passing through Basirhat in North 24-Parganas, around 75km from the heart of the city.
“The deep depression over Gangetic West Bengal moved west-northwestwards with a speed of 20kmph during the past six hours and lay centred at 8.30am... close to Bankura. It was 70km from Purulia and 180km from Ranchi. It was likely to move west-northwestwards across Jharkhand and weaken gradually into a depression,” a Met bulletin issued on Wednesday afternoon said.
Though the sky remained cloudy almost throughout Wednesday, the rain was negligible in Kolkata.
“Thursday is expected to be brighter. But some moisture is there in the atmosphere as remains of the system. If there is sufficient heating, thundershowers are expected in Kolkata on Thursday,” said G.K. Das, director, India Meteorological Department, Kolkata.
The deep depression, the most powerful system on the Bay this season, led to the highest volume of rain that Kolkata has seen in 24 hours since the arrival of the monsoon on June 19.
The system is likely to remain active for three more days, triggering rain in central and northwestern India, Das said.
“The districts of north Bengal may get more rain in the next few days,” a Met official said.