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Monsoon arrival expected around June 11, says IMD

PUBLISHED ON JUN 06, 2020 11:37 PM IST

The arrival of the southwest monsoon can be expected over the city next week close to its new normal onset date of June 11, the weather bureau said.

As a low-pressure area (weather system) develops over the Bay of Bengal around June 8, the India Meteorological Department (IMD) said it will enhance rainfall activity over the coast, especially the Konkan region, including Mumbai.

“Based on examples witnessed in previous years, and our weather models, when a low-pressure system develops over the Bay of Bengal, it leads to rainfall activity over the west coast due to changing wind patterns and increased moisture incursions. It is a positive development as it will allow the further advancement of monsoon, and most probably it will meet its new normal onset date of June 11 for Mumbai,” said Mrutyunjay Mohapatra, director-general, IMD.

Last month, IMD revised its normal onset date for major cities across India and declared that the arrival would be delayed by a day (from June 10 to June 11) and withdrawal date by nine days (from September 29 to October 8). This means the southwest monsoon is likely to have an extended stay for eight days from this year onwards, according to IMD.

Independent meteorologists were divided over the possible monsoon onset date.

Sridhar Balasubramanian, associate professor, department of mechanical engineering and associate faculty, IDP Climate Studies, Indian Institute of Technology-Bombay (IIT-B) explained that due to the system over the Bay of Bengal, an offshore trough (weather system due to strong wind currents) would form along with a possible cyclonic circulation (a stream of air flowing at higher altitudes) in the Arabian Sea, close to Gujarat.

“Heavy rains to the tune of 90-100 mm is generally seen over Mumbai. Given these dynamics, June 12 is likely onset over Mumbai followed by some heavy rains anytime between June 13 and 15,” said Balasubramanian adding that the offshore trough will extend from Mumbai to Kerala coasts. “Hence, the west coast will generally see heavy rains between June 10 and 15. The heavy rain window for states will be different given the strength of offshore trough. For eg Kerala and coastal Karnataka are likely to see heavy rains between June 10-12. Goa and Ratnagiri belt (south Konkan) may see heavy rains between June 11-13.”

Akshay Deoras, independent meteorologist and PhD researcher at the University of Reading, UK said several models were suggesting that monsoon would reach Konkan and Mumbai between June 14 and 16. “Proper rainfall is expected to commence in Mumbai from around 12 June. Arrival over interior Maharashtra is expected through the week starting June 15.”

Private weather forecasters Skymet said onset was expected between June 12 and 13.

Meanwhile, the IMD also released the lifecycle of Cyclone Nisarga that battered several areas of the Maharashtra coast, and its final trajectory ending up over parts of southeast Uttar Pradesh and adjoining Bihar as a low-pressure system. This was the first time IMD issued a ‘pre-cyclone watch’ at 2 pm on May 31, at the stage when the weather system was a low-pressure area, 80 hours before the landfall as a severe cyclonic storm. “This was the first time in history where we went a step ahead and issued a cyclone warning to both states before the system developed into depression or deep depression, which is our standard operating procedure. It gave both Maharashtra and Gujarat a day more than usual to prepare for its arrival,” said Mohapatra adding that the very first information about the system was provided on May 29, three days before the formation of a significant system.

Monitored using observations from various satellites, ships, and buoys (instruments which collect weather and ocean data), IMD provided three-hourly bulletins from June 1 to 2, and hourly bulletins on June 3 and 4, including rainfall, wind warnings, affected districts, location of the system, expected property damage, storm surge, and location of landfall.

‘If the location of landfall was more accurate, the response would have been faster’

Though the cyclone brushed past Mumbai not causing much damage to the financial capital, the extent of damage was witnessed along southern talukas of Raigad district. While the extent of landfall area, as per IMD’s prediction, ranged from Daman, south Gujarat to Harihareshwar in Raigad, the forecast till 5am, June 3 read landfall would be ‘close to Alibag’. This allowed necessary responsive measures within that area. However, at 10 am June 3, the location was slightly altered to the south of Alibag, forcing a sudden change in responsive measures. Landfall took place at 12.30 pm near Diveagar between Shrivardhan and Murud, south of Alibag but the extent of damages in these areas were only identified three days after landfall as authorities were unable to reach these areas. Deoras said the landfall process as per the radar commenced around 10am, but IMD’s 12pm bulletin expected it to start during 1230 and 1pm. “In reality, most of the process had finished by 1pm,” he said.

Mohapatra countered stating that the landfall site was accurate as per the large area provided (from Harihareshwar to Daman). “Even the wind speed after landfall was as predicted. It is a dynamic system and can change dramatically closer to land. However, as in the case of Mumbai, it was better to have heightened safety measures than witnessing losses,” he said.

“The landfall hit regions in Raigad district such as Diveagar will also witness proper rainfall from around June 12. This is likely to cause more inconvenience and disruptions in the rehabilitation process,” Deoras added.

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