Downpour...

The city has so far received 2,366mm rain between June 1 and August 5 (8.30pm) against its seasonal average of 2066mm. The Santacruz weather station, representative of the suburbs, has recorded 2,356.9mm rain during the same period against its seasonal average of 2260.4mm. In 59 hours till 8.30pm on Wednesday, the city has received 456mm rain.

The weather bureau, however, said rain intensity is likely to reduce from Thursday and a yellow alert (heavy rain in isolated areas) has been issued after two days of red alert.

“South Mumbai witnessed 30-50mm rain per hour, falling under the very intense rain spell category, on Wednesday. The low pressure area over north Bay of Bengal adjoining Odisha draws winds (pull-effect) from the Arabian Sea over coastal areas, and the upper air cyclonic circulation over parts of south Gujarat. Both activate strong monsoon conditions. These high speed winds characterise the intensity over coastal areas,” said Mrutyunjay Mohapatra, director-general, IMD, adding that the systems draw moisture from the sea, leading to convective cloud formation, which intensified over south Mumbai and later moved towards the suburbs. “Although similar weather conditions will last till Wednesday night, the situation is likely to improve on Thursday.”

Mahesh Palawat, vice-president (meteorology and climate change), Skymet, said, “The formation of such convective clouds (10-14km above mean-sea level) witnessed over south Mumbai on Wednesday was a rare event. We are witnessing such events, where convective clouds are dissipating and regenerating continuously due to overall changing weather patterns. This is a pre- or post-monsoon type rain phenomenon capable of giving high speed surface winds drawing continuous moisture from the sea.”

Independent meteorologists said the wind pattern exhibited anti-clockwise nature due to a vortex formation (spinning column of air caused by weather factors enhancing monsoon conditions). “This brought rain clouds and pushed them to move over south Mumbai. They weakened rapidly after crossing south Mumbai, thereby leading to less rain over the suburbs,” said Akshay Deoras, independent meteorologist and PHD researcher at the University of Reading, the United Kingdom.

Meanwhile, water stock across seven lakes supplying water to Mumbai was 35% of the required amount. It was 90% last year by this time. “With very heavy showers underway over these areas, we expect improvement in levels over the next 48 hours,” said an official from the Brihanmumbai Municipal Corporation (BMC).

Deoras said Thursday evening onwards the weather in Mumbai region would stabilise. “No severe weather threat is expected during the weekend since at the most intermittent light showers are possible,” he said.