Monsoon ends 70mm short of all-time high in Mumbai; 67% excess rain over four months

As the curtains came down on the official four months of the southwest monsoon, Mumbai recorded its second-wettest monsoon in history, just 70mm short of the wettest-ever.

As the curtains came down on the official four months of the southwest monsoon, Mumbai recorded its second-wettest monsoon in history, just 70mm short of the wettest-ever.

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The highest all-time seasonal rainfall was recorded in 1958 at 3,759.7mm, according to the India Meteorological Department (IMD); making monsoon 2020 rainfall the highest in 61 years.

This year monsoon onset was officially declared on June 14, three days beyond its normal onset date. However, southwest monsoon from June to September came to an end with almost 1,500mm more rain than the average rainfall during the four months.

Santacruz weather station, representative of the suburbs and Mumbai, recorded 3,687mm rain against the seasonal average of 2,260 mm between June 1 and September 30, which means an excess of 1,481mm or 67% rain.

Similarly Colaba weather observatory, representative of south Mumbai, recorded 3,202.5mm during the same period, against the average of 2,066mm. South Mumbai received 1,181.5mm or 58% excess rain for the season, which is the highest since 1984.

“Total seasonal rainfall for Colaba and Santacruz from June to September has been exceedingly well with departures of more than 1,000mm. Day-wise rainfall progress from June to September indicated that the rain pattern in the city and suburbs almost remained identical till August and it slowed down from September, apart from a major rain spell during the third week,” said KS Hosalikar, deputy director general, western region, IMD.

Over the four months, the season saw four extremely heavy rain events — one in July, two in August, and one in September, 11 very heavy rain events between July to September, and nine heavy rain days, calculated over 24 hours for Colaba and Santacruz. The heaviest one-day rain spell this season was on August 5-6 at 332.1mm rain at Colaba followed by 286.4mm rain on September 22-23 at Santacruz. Mumbai also recorded 268.6mm rain on August 3-4 and 200.8mm between July 4 and 5.

Maximum rain was recorded in July at 1,502.7mm, the highest since the weather bureau started collating records in 1944, followed by the highest August rainfall since 1959 at 1,247.6mm. While June recorded its lowest rainfall in five years at 395mm, 60% excess rain was recorded in September at 549.1mm.

IMD has predicted monsoon withdrawal from Mumbai and Maharashtra between October 9 and 15. Independent meteorologists said that from this weekend, the Mumbai Metropolitan Region (MMR) could once again witness post-noon thunderstorms. “This is likely to continue until the middle of next week. Monsoon’s withdrawal from the region appears unlikely before October 10. The most probable window as per the current forecast seems to be between October 15 and 20,” said Akshay Deoras, independent meteorologist and PhD researcher at the University of Reading, the United Kingdom.

Overall, Maharashtra witnessed 16% excess rain with 1,165mm recorded over four months against the average of 1,004.2mm. Central Maharashtra and Marathwada recorded 29% and 30% excess rain. Only three districts in Vidarbha — Akola, Amravati, and Yavatmal — recorded 27%, 20%, and 24% deficient rain in Maharashtra this season. Sindhudurg recorded maximum rainfall over four months at 4,485.4mm which is 53% more than the average.

“Maharashtra witnessed satisfactory seasonal rainfall in 2020 with Marathwada witnessing excess rains. The overall distribution of rains remained good throughout, leading to a good monsoon season for farmers in the state,” said Hosalikar.

MONSOON 2020 ACROSS INDIA

India witnessed ‘above normal’ rainfall at 109% of the long period average (LPA) this year. India defines average or near-normal rainfall as rainfall between 96% and 104% of a 50-year average of 89cm for four months. Pan-India, 957.6mm rain was recorded against the normal of 880.6mm; this makes this the second best monsoon since 1994, the best being 2019 which ended with 110% of LPA.