Blinding rain and relentless streaks of lightning swept through Calcutta on Thursday afternoon, flooding hospitals, choking traffic and throwing life out of gear.
The downpour made the already challenging rescue operation at the site of the Garden Reach warehouse collapse even more gruelling. The site was waterlogged and rescue personnel had to deploy suction jets to drain out water.
If the rain was intense, the lightning unnerved many across the city. Blinding violet-white flashes repeatedly tore through the dark sky, forcing many indoors and thinning traffic on the roads.
“I was watching news channels showing images of the quake-ravaged Venezuela. But after a while, I switched off the TV because of the lightning streaks. The windows were shut, but every now and then a flash seemed to pierce through,” said Sarbani Ganguly of New Alipore.
A Met official said the flashes appear closer during cloud-to-ground strikes such as those seen on Thursday. These are the bolts that kill people. Fortunately, no casualties had been reported till evening.
A flash of lightning is an electrical discharge triggered by an imbalance between clouds and the ground, or between clouds themselves. The discharge heats the surrounding air to temperatures far higher the surface of the sun, causing the air to explode outward and generate the thunder that follows.
At SSKM Hospital, a group of relatives of patients admitted to the trauma care unit rushed indoors when a bolt appeared to strike near a row of parked cars in the compound.
Waterlogging
The compounds of SSKM Hospital and RG Kar hospital were flooded by 3.30pm. Hassled relatives of patients struggled to move between different wings of the sprawling campuses, which lack basic passenger amenities.
School dispersal was delayed as buses were stranded on waterlogged roads.
The Met office recorded close to 85mm of rain in Alipore between 8.30am and 5.30pm on Thursday. Most of it fell between 2pm and 3.30pm, a Met official said.
Kalighat received 90mm of rain and Behala 85mm, according to readings at civic body pumping stations there. North Calcutta was hit harder. Belgachia received 114mm during the same period. In Met parlance, 60mm of rain in 24 hours qualifies as “heavy rain”.
Thursday’s peak wind speed was 63kmph, recorded around 2pm.
Traffic hit
Vehicles crawled across the city through the afternoon and evening. A journey from Sector V to New Town, which usually takes around 15 minutes in modest traffic, stretched beyond an hour.
Even after the rain had eased into a drizzle, travelling from Park Circus to Esplanade took over an hour in the evening. Camac Street, Park Street, Theatre Road, Sarat Bose Road, Central Avenue, MG Road and College Street were among the roads where vehicles moved at a snail’s pace.
Red alert
The sky was partly cloudy in the morning. As the day progressed, the clouds grew steadily darker. Minutes before 2pm, it had become so dark that many motorists switched on their headlights. What began as a light shower intensified rapidly into a fierce spell of rain.
Around 2.15pm, the Met office issued a “severe thunderstorm and intense rain” warning. It was a red alert, advising people to take evasive action.
For most Calcuttans, it came a little too late. They already knew this was not just another thunderstorm.
This was the third spell of heavy rain in Calcutta in less than a week.
Unusual monsoon
The monsoon arrived in Calcutta on June 11. But these spells are not the typical monsoon rain that Calcutta is used to. All three spells over the past week have been thunderstorms, more commonly associated with the pre-monsoon months of April and May.
A Met official explained the reason.
“Monsoon may be vigorous in Bengal, especially north Bengal, but not in the rest of the country. The monsoon currents are weak across swathes of central India,” said H.R. Biswas, head of the Regional Meteorological Centre in Alipore.
“In such a situation, Bengal is witnessing a difference in moisture content across different layers of the atmosphere. Closer to the surface, moisture-laden southerly and southwesterly winds are dominant. But higher up, dry-weather winds prevail. With sufficient heating, the interaction between the moist and dry winds is leading to the formation of strong thunderclouds,” he said.
That also explains the frequent lightning. The stronger the thunderclouds, the greater the chances of lightning.
While monsoon currents remain stronger in north Bengal, south Bengal is likely to continue witnessing thunderstorms over the coming days, although the intensity may vary.