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Why Mumbai woke up to a wet morning; IMD attributes unseasonal rain to deep depression in Arabian Sea

Vinson Kurian Thiruvananthapuram | Updated on December 05, 2019 Published on December 05, 2019

A file photo from last month. November saw Mumbai record its highest-ever rainfall. Citizens are worried that more rain will follow this month, delaying winter PAUL NORONHA

Thane, Dadar, Kalyan, and Mulund reported light rain; residents worry more will follow after the record rainfall in November

After heaving a collective sigh of relief that November and its record-high rainfall were behind them, people in some parts of Mumbai were surprised to wake up to an unseasonally wet December morning. The Maximum City’s denizens took to Twitter to express their worry about the implications of the unexpected showers. The rain had come at a time when they were expecting the winter chill to set in. In fact, warm south-westerly to south-easterly winds (instead of cooler north-westerly) had rudely interrupted the build-up to winter.

The India Meteorological Department (IMD) attributed the unseasonal rains to a deep depression in the Arabian Sea that was to intensify as a cyclone yesterday but relented this morning. Light rain was reported from several parts of the city, including Thane, Dadar, Kalyan, and Mulund.

It was enough to ruffle some feathers and tweets flew far and wide talking about global warming/climate change while others posted funny memes. #MumbaiRains ended up trending on Twitter.

Mumbai experiences three distinct seasons: Winter (November to February or mid-March); Summer (February/March to mid-June and September to November); and monsoon: (June to August, at times until October). Thursday morning was special because of the depression. The winds were from the sea and carried moisture; and moisture means warmth. Normally, winter winds in December should originate from North-West India, driven by the seasonal anticyclone that sits over the region.

November record

The monthly rainfall in November has been the highest ever in Mumbai, according to the IMD. The previous all-time high was recorded in November, 1979. Rainfall in November is rare for Mumbai, and this year, it was attributed to the influence of cyclone Maha. In fact, on November 1, unseasonal rain from the afternoon due to cyclone Maha led to Mumbai recording its highest 24-hour November rainfall of 46.3 mm in 10 years.

KS Hosalikar, Deputy Director-General, IMD, Mumbai, tweeted on Thursday morning that a “very light drizzle” was reported from isolated places in the city. It was cloudy over the city and parts of Maharashtra. Partly cloudy conditions were forecast for Mumbai and Thane for today, with chances of light rain or a drizzle.

There are two low-pressure systems in the Arabian Sea, with the one in the east-central Arabian Sea being closer to the Maharashtra-Goa coast. Low-pressure systems often trigger disturbed, wet weather in nearby regions. As of Thursday morning, this depression in the East-Central Arabian Sea was located about 690 km west-southwest of Mumbai (Maharashtra) and 620 km of west of Panjim (Goa).

Combined effect

This rainy weather is basically the combined effect of cyclone Pawan farther away in the South-West Arabian Sea and a depression nearer home over the East-Central Arabian Sea. But the latter is moving away from the West Coast India and hence there was no warning for heavy rainfall at any place in Maharashtra and Goa. But strong winds with speeds reaching up to 40 km/hr may prevail along and off these coasts till Thursday evening.

Mumbai has already received 18.5 cm of rainfall during the post-monsoon season so far from October 1 to December 5, which is 53 per cent above normal. The warmth brought about by the moisture carried from the depression will only delay the arrival of the cooler weather associated with the winter, and that seems to be worrying the Mumbaikars!

 

 

 

 

Published on December 05, 2019
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