An 88kmph Nor’wester swept through Calcutta on Friday afternoon, bringing blinding rain, uprooting trees, killing at least one person, injuring at least five commuters, disrupting flights and trains, and exposing the city’s vulnerabilities, still in transition after the Assembly election results.

Seven deaths were reported across south Bengal, said a government official. Howrah, Hooghly, East and West Midnapore were among the worst-affected districts.

A young man died of suspected electrocution near Prinsep Ghat around 3pm while collecting mangoes under a tree, police said. Lightning struck the tree, and a branch fell on an overhead wire along the circular railway line. The wires caught fire, stalling trains between Dum Dum and Majerhat for several hours.

At least 60 trees were damaged, with around 40 completely uprooted.

Flight operations at Calcutta airport were suspended for an hour from 2.20pm. Metro services on the Blue Line were halted between Tollygunge and Shahid Khudiram, and from Girish Park to Dakshineswar, for nearly 30 minutes.

A portion of the façade of South City Mall was damaged.

The storm was the fiercest this squall season. At 2.47pm, the Met office recorded a wind speed of 88kmph at Alipore.

On March 16, the onset of the squall season was marked by a Nor’wester that clocked 72kmph at Alipore.

Light rain is likely in and around Calcutta on Saturday as well. “But the intensity will be lower,” said a Met official.

The storm briefly cooled a parched city reeling under heat and humidity.

Traffic was disrupted on major roads due to fallen trees and branches. On Southern Avenue, a large branch fell on a moving car. Trees were uprooted on Harish Mukherjee Road, Race Course, Mayo Road, Red Road and Tallah Park.

Strong winds tore billboard flexes off metal frames. Several stretches remained waterlogged long after the rain stopped.

The Met office recorded 40.5mm of rainfall at Alipore.

The storm began around 2.20pm, with peak intensity lasting till about 3pm.

Flight movement was suspended between 2.21pm and 3.20pm, said an official of the airport. “No flight was cancelled, but around 20 were delayed,” the official said.

At least five flights were diverted. Flights from Bengaluru, Patna, Agartala and Mumbai were affected. Two Bengaluru flights were diverted to Agartala; one each from Patna and Mumbai to Bhubaneswar, while another from Agartala returned to its origin. All later landed in Calcutta after conditions improved.

Metro officials said Blue Line services were stopped on elevated sections from 2.55pm to 3.16pm as a precaution. Normal services across the full stretch between Dakshineswar and Shahid Khudiram (Briji) resumed after 3.16pm.

Train services on the Sealdah North suburban section were also disrupted, especially on the Sealdah-Bongaon line.

A spokesperson for South City Mall said: “A few glass panels on the mall’s façade were damaged in the storm. Our teams cleared the area. No injuries were reported.”

A Nor’wester is a squall that originates over the heated Chota Nagpur Plateau in the afternoon and sweeps across eastern India over three to five hours at speeds above 45kmph. It is usually followed by rain. Friday’s storm ticked all these boxes.

“A change in wind pattern allowed greater moisture incursion into south Bengal, while accumulated heat and humidity aided the formation of tall thunderclouds over the Chota Nagpur Plateau, or the Bengal-Jharkhand border,” said H.R. Biswas, head of the Regional Meteorological Centre in Alipore. “These thunderclouds formed a squall line from Bihar to coastal south Bengal. It intensified as it moved coastward because of moisture from the Bay. By the time it reached Calcutta, the cloud towers were nearly 15km high.”

The taller the clouds, the stronger the winds, a scientist said.

Chief minister Suvendu Adhikari announced an ex gratia of ₹4 lakh for the bereaved families. His office directed Agnimitra Paul, urban development minister, to take stock of the damage.