KOLKATA: An unexpected change in the trajectory of a low-pressure system, brought on by a retreating monsoon, was responsible for the devastating rain that crippled the north Bengal plains and hills.
The system, which formed over Bay of Bengal on Sept 30, hit land in Odisha as a depression and was sailing north-northwestward towards Chhattisgarh when it suddenly recurved towards north Bihar, coming dangerously close to north Bengal.
Despite gradual weakening since entering land, the system was strong enough to dump heavy rain on Kalimpong, Kurseong, Alipurduar, Cooch Behar, Jalpaiguri and Darjeeling, flooding vast swathes of north Bengal.
'Westerly winds brought system closer to state' The system weakened into a 'well-marked low-pressure area' on Saturday and was hovering over north-east Bihar as a cyclonic circulation on Sunday. Meteorologists said the system was headed towards Chhattisgarh on Friday when it suddenly took a north-eastern turn due to strong westerly winds.
"Since the monsoon is now retreating from north India, there were strong westerly winds that diverted the system towards north Bihar, bringing it closer to north Bengal. It was prevented from approaching central India... The 'recurve' was unexpected but not unusual," said a meteorologist.
The system moved towards N Bihar while it was still a 'well-marked low-pressure' belt. "Though not very intense, these systems spread across a wide region. North Bengal fell within its periphery. In fact, Kolkata, too, continues to be impacted by the system," he said. Even though it weakened into a low-pressure area from depression, it affected N Bengal significantly due to strong winds and moisture incursion, said Sourish Bandopadhyay, RMC scientist.
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