Suburban Mumbai — representative of the entire city — on Friday witnessed the season’s heaviest rainfall with the India Meteorological Department’s (IMD) Santacruz observatory recording 253.3 mm of showers – the second-highest rainfall in 24 hours in a decade between July 15-16.
In 2019, between July 1-2, the Santacruz observatory had reported 375.2 mm of rainfall, which had been the highest one-day rain recorded so far in the last 10 years. With the Thursday night downpour, the city has recorded 70.5 per cent of the average July rainfall, in 16 days. The average July rainfall is 827.5 mm.
South Mumbai, meanwhile, was relatively dry with IMD’s Colaba observatory recording light rain at 12.8 mm.
The difference in rainfall in the city and suburbs was one of the largest spatial discrepancies over the 25 km distance between the two observatories.
The rainfall recorded by the Santacruz observatory falls in the “extremely heavy rain” category. However, an extremely heavy rain warning was not issued by the IMD for Mumbai or adjoining areas for Friday. The district forecast warning had issued a yellow alert of heavy rainfall at isolated places.
When asked, Jayanta Sarkar, head of the Regional Meteorological Centre in Mumbai, said: “There are two components in forecasting – intensity and distribution. We predicted the distribution of rainfall correctly, but the intensity, which was confined to the western suburbs, could not be predicted given that the cloud cover formed extremely quickly and during the early hours.”
As per the regional forecast issued by IMD, Konkan region, including Mumbai, is likely to receive widespread rainfall till July 20. A widespread rainfall distribution signifies that 76-100 per cent of stations in a region will receive rainfall. The IMD said Mumbai is very likely to get heavy rain at isolated places on Saturday. From Sunday till Tuesday, it is very likely to receive heavy to very heavy rain at isolated places.
While IMD officials said that they are studying the reasons behind the sudden influx of extremely heavy rain, independent meteorologists said localised weather systems contributed to the heavy rainfall.
“Satellite images show that a strong thunderstorm formed over the suburbs early in the morning. As it matured, winds from the east moved it away from the city, resulting in very less rain over Colaba and southern parts of the city. It was not the usual heavy rainfall event in which Mumbai-MMR witnesses widespread and sustained heavy downpour. Mountains in the suburbs could have played an important role in triggering the thunderstorm,” said Akshay Deoras, independent meteorologist and PhD researcher at the department of meteorology, University of Reading, UK.
Deoras added in such events, doppler radars are crucial in sending out heavy rainfall warning alerts. “It will be surprising if any of the current operational weather models predicted a localised event like this. This is why we need doppler radars, which tell you where clouds are forming, how intense they are and which regions will be impacted. If the doppler radar at Mumbai was working well and scanning at an interval of 10-15 minutes, it would have helped a meteorologist to send timely alerts.”
The IMD in the morning updated Friday’ forecast – heavy to very heavy rain at isolated places – with an orange alert. However, the island city and suburbs received light rain through Friday. In nine hours beginning from 8,30 am, the Santacruz observatory recorded 14.1 mm of rain while Colaba centre recorded 4 mm rain.
BMC’s rain data showed that between 4 am and 9 am on Friday, maximum of 186 mm of rainfall was recorded in H-East ward, which includes parts of Bandra East, Kalina and Vakola. It was followed by M West ward (Chembur), which received 175.5 mm of rainfall. Other wards that saw high rainfall were K West (Andheri) at 159 mm.