3rd highest single-day rainfall in Kolkata after 1978, 1986: Was it a cloudburst? Here’s what IMD says

“The city of Kolkata received 251.4 mm of rainfall, a figure recorded at 8:30 am on September 23,” said an official. Kolkata Mayor Firhad Hakim had earlier said that he hadn’t seen such flooding since the major floods of 1978.

“Although the highest hourly rainfall was 98 mm, it did not meet the criteria for a cloudburst, which typically requires more than 100 mm per hour,” said a senior official of the IMD.

Causes and IMD forecast

The heavy rainfall was triggered by a low-pressure area that formed on September 22. This system moved towards the coastal areas of Gangetic West Bengal and adjoining regions, leading to a strong convergence of moisture over Kolkata. “Doppler weather radar images showed high moisture content with clouds reaching heights of 5 km to 7 km, contributing to the intense downpour,” said the IMD.

People row a boat in a waterlogged area following rainfall, in Kolkata, Tuesday. (PTI photo)

The low-pressure system is expected to persist until Wednesday before becoming less marked. However, another low-pressure area is predicted to form over the Bay of Bengal around September 25, which could intensify into a depression and cross the South Odisha-North Andhra Pradesh coasts around September 27.

This developing weather pattern is expected to bring widespread light to moderate rainfall, with isolated heavy to very heavy rainfall possible in some districts of South Bengal over the next seven days.

Hakim described the flooding as unprecedented in his memory, noting that even neighbourhoods near the Adiganga, which normally drain well, were overwhelmed. The overflowing of the Adiganga, a canalized river, prevented natural water runoff.

In response to the flooding, authorities have opened several school buildings to provide shelter for people from low-lying areas and those living on the streets. The Corporation and the police have been tasked with arranging food for the displaced. The Mayor expressed hope that the water would recede by night if no further rain occurred.

The heavy rain has also led to a warning for fishermen, advising them not to venture into the sea along the West Bengal-Odisha coast until September 27 due to rough sea conditions and squally weather. “Residents are also advised to avoid taking shelter under trees or electric poles and to be cautious of lightning strikes,” read an IMD alert.