Trough after low pressure prolongs wet spell

Kolkata: The city was drenched by heavy showers on Tuesday that were triggered by a sudden and unpredicted movement of the monsoon trough from the Bay of Bengal to Gangetic Bengal. Along with Kolkata, the neighbouring districts of South 24 Parganas and North 24 Parganas, Howrah and Hoogly, too, were hit by repeated spells of torrential rain that continued through the day. The rain may continue in Kolkata for the next 48 hours, said Met office, though it is likely to be moderate.

A day after intermittent showers lashed Kolkata on Monday — under the impact of a deep depression over Bay of Bengal that moved towards Odisha and central India — heavy showers struck Kolkata early on Tuesday, taking even weathermen by surprise. “While we had expected the rain to lose intensity by Tuesday afternoon since the depression had moved away from Kolkata, the monsoon trough, that was stationed across Bay of Bengal, suddenly surged upwards towards south Bengal. It carried a huge mass of cloud with it that triggered intense showers in Kolkata and its surrounding districts,” said Regional Meteorological Centre (RMC) director GK Das.

With the depression moving away from the state, a ‘pressure gradient’ had been created that pulled the monsoon trough towards south Bengal, added Das. “Now that the depression has moved further away and lost strength, the gradient, too, will wane and the trough will trigger light to moderate rain,” explained Das.

The monsoon trough, though, will continue to pass through south Bengal.

“The system had started moving away from Bengal towards Chhattisgarh and Madhya Pradesh on Monday. So, it was expected to lose intensity. But the monsoon trough sprung a surprise,” said Das.

Another low-pressure may form over Bay of Bengal around September 19 but it was too early to predict its intensity, said the Met office.


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