At over 300mm, Mumbai records season’s first day of extreme rainfall

Mumbai: Heavy rains lashed most parts of the city late at night on Sunday and Monday, with several places registering over 300mm rainfall in a span of six hours. The heaviest downpour was recorded between 2.30am and 5.30am, mainly in the eastern and western suburbs, making Monday the season’s first day of extreme rainfall in the city. This was contrary to forecasts of moderate rainfall issued by various weather agencies, who attributed the spike to an offshore trough along the western coast. At 5.30pm on Monday, the India Meteorological Department (IMD) placed Mumbai under a red alert, effective till 8.30am Tuesday.

According to the IMD, in the 24 hours between 8.30am on Sunday and 8.30am on Monday, Santacruz recorded 268mm of rainfall while Colaba trailed behind at 84mm. According to data from the Brihanmumbai Municipal Corporation’s (BMC) automatic weather systems (AWS), between 8am on Sunday to 8am on Monday, the average rainfall in the island city, the western suburbs and the eastern suburbs was 115.63mm, 165.93mm and 168.68mm, respectively. The places that received nearly 300mm rain between 1am and 7am on Monday were Bhandup (315.6mm), Powai (314.6mm), Malpa Dongari in Andheri East (292.2mm) and Chakala (278.2mm).

The island city received heavy rain throughout the day on Monday, with Colaba recording 134.8mm compared to Santacruz at 72.2mm between 8.30am and 8.30pm. Rain in the suburbs picked up after the IMD issued a red alert in the evening, with Andheri West, Ghatkopar and Kurla receiving the most showers.

All weather agencies had forecast moderate showers in the city on Monday. The IMD had issued a yellow alert for the day, indicating heavy rainfall at isolated places, while Skymet had forecast light to moderate rains. Even IIT Bombay’s Climate Studies Department failed to forecast any extremities despite the deployment of a new forecasting model.

“There was an offshore trough along Gujarat stretching all the way till the north Kerala coast, which strengthened along the north Konkan coast around midnight,” said Sushma Nair, scientist at IMD Mumbai. “Such small-scale weather systems are hard to predict, as they develop quickly and occur over a limited spatial area and span of time.” The IMD had issued an orange alert at 12:30am, she added, forecasting heavy to very heavy rainfall with thunder, lightning and gusty winds.

“All our weather forecasting models failed us,” said Subimal Ghosh, convener of IIT’s climate studies programme. Echoing Nair, he said some weather systems were hard to predict, especially because Mumbai was located along the coast, with varied terrains in the vicinity. “We will have to understand what transpired and incorporate the lessons into our models to let it learn from nature,” said Ghosh.

The offshore trough along the south Gujarat-north Kerala coast still persists along with a sheer zone and it is likely to bring more rain to the city, said Nair.

“We have issued a yellow alert for Tuesday, indicating heavy rains at isolated areas, followed by a green alert for Wednesday. Another active spell of rain is forecast on July 11,” she said.