Monster cloud triggers heavy rain, leaves Kolkata flooded

KOLKATA: A day after a cumulonimbus cloud column plunged the city into darkness, Kolkata woke up to a grey sky and steady showers on Tuesday morning. The peripheral effect of a cyclonic circulation, the showers were heavy in parts of the city. Areas like Behala, Jadavpur, Jodhpur Park and stretches along EM Bypass were left waterlogged.
The Jinjirabajar pumping station in Behala recorded 123mm of rain between 8 and 10 am.
There was little respite in sight for the city with more rains predicted in the next 24 hours. A low-pressure system has started forming on the Bengal coast and is moving northward towards south Bengal, the met department said. "A cyclonic circulation now lies over a low-pressure area that is forming on the Bengal coast. It will lead to rains on Wednesday. There could be heavy spells but the showers would lose their intensity by Wednesday afternoon," said GC Debnath, director of the Alipore weather office.
Even though the rain stopped early in the afternoon, office-goers had a tough time wading along ankle-deep water. Roads were flooded at Ultadanga, Paikpara and Tullah
in north Kolkata. Behala was the worst-affected in the south with Shilpara, Shakherbajar and Taratala being waterlogged for hours. Stretches of Chittaranjan Avenue, Amherst Street and the area around Thanthania were flooded as well. "The showers were the peripheral effect of a cyclonic circulation. Since the moisture incursion was not very high, the clouds dissipated soon," said Devendra Pradhan, deputy director-general, meteorology department. He added that the low pressure that has formed on the coast was not a very alarming one. "It is yet to intensify. It will lead to some rainfall in the city. But the showers should lose intensity by Wednesday afternoon," Pradhan said.
The showers on Tuesday, however, were not triggered by the giant 12 km-tall cumulonimbus column that had formed on Monday afternoon, plunging the city into darkness at noon. Weathermen said had that been the case, it could have led to a deluge strong enough to flood the city. The fact that it brought 67 mm of rain in Salt Lake and 20 mm in Kolkata in just one hour was indicative of its potential, said experts. It was the terrain condition that saved Kolkata. It was a close shave for the city's drainage system that can absorb only 8-10 mm of rain per hour.
Due to the high temperature, the raindrops, ice flakes and snow that formed within the 12 km tall, 100 km long and 50 km wide cloud column were smaller. Had it formed in the hills, where temperatures are lower, the contents of the cloumn would have been bigger, leading to a heavier downpour. That could also have led to a cloudburst. "In the hills, such cloumns almost invariably lead to a clouburst and a disaster. The bigger raindrops, snow and hail make it heavier, leading to a heavy deluge. But due to different orography or terrain condition in the plains, cumulonimbus columns like the one which formed on Monday lead to heavy downpour which lasts for a short period. Since the rain drops and iceflakes are smaller, they start dissolving fast, unlike in the hills," explained Pradhan.
On Tuesday, Ballygunge recorded 51 mm of rain, Jodhpur Park 53 mm, Dhapa 46 mm, Palmer Bazaar 43 mm, Ultadanga 45 mm, Thanthania 49 mm, and Cossipore 46 mm. BT Road, Chittaranjan Avenue, Sukia Street, parts of AJC Bose Road, Behala, Jadavpur, stretches of EM Bypass and Tiljala were left waterlogged