Mumbai records most delayed south-west monsoon withdrawal since 1975
Prior to this year, the most delayed withdrawal of monsoon from Mumbai was recorded on October 26 in 2010. Monsoon had withdrawn from the city on October 24 in 2011 and 2017Updated: Oct 28, 2020, 14:53 IST
Mumbai reported the most-delayed withdrawal of monsoon since the India Meteorological Department (IMD) started maintaining records in 1975.
The IMD declared the south-west monsoon withdrawal from Mumbai, the rest of Maharashtra and the country on Wednesday (October 28).
Prior to this year, the most delayed withdrawal of monsoon from Mumbai was recorded on October 26 in 2010.
Monsoon had withdrawn from the city on October 24 in 2011 and 2017.
“This is definitely one of the most delayed withdrawal of monsoon from the country. It is also the most delayed withdrawal from Mumbai and Maharashtra,” said M Rajeevan, secretary, Union Ministry of Earth Sciences (MoES).
He attributed the reason to the presence of La Niña.
La Niña is a weather pattern, where the western Pacific Ocean warms up creating a low pressure near Australia, pulling winds from the Indian Ocean and strengthening equatorial dynamics while keeping south-west monsoon circulation active.
“During La Niña years, we tend to get extended monsoon and more rainfall. Conditions were favourable for sustaining those conditions for a longer time. Both the Pacific Ocean and the Indian Ocean were very active this year,” said Rajeevan.
In April, the IMD had announced the new monsoon onset date for Mumbai as June 11, against June 10, and the new withdrawal date as October 8, against September 29.
The normal duration of the monsoon season over Mumbai this year was expected to span over 120 days -- from June 11 to October 8 -- as opposed to 112 days – from June 10 to September 29.
The forecast turned out to be wrong as monsoon spanned over 136 days --from June 14 to October 28.
This year, the onset of monsoon was declared on June 14, three days later than the prediction.
Last year, monsoon withdrawal from Mumbai was declared on October 14. In 2018, it was on October 6.
“In view of significant reduction in rainfall activity over most parts of the country, the south-west monsoon has withdrawn from the entire country on Wednesday. Simultaneously, with the setting in of north-easterly winds in the lower levels of troposphere, the north-east monsoon rainfall commenced over extreme southern peninsular India on Wednesday (October 28),” an IMD release stated.
Rajeevan said delayed withdrawals and late monsoon onset have emerged as a pattern.
“In June, when we revised the onset and withdrawal dates, it was done keeping in mind an extension of the monsoon season. The onset and delayed withdrawal of monsoon has become a recurring phenomenon,” he said.
Over 136 days this monsoon, Mumbai recorded a total rainfall of 3,857.1 millimetres (mm) against the annual average of 2,514 mm.
According to IMD, this is the highest rainfall recorded in at least a decade for the June–October period.
It was the second-highest rainfall (3,687mm) for the June-September period since readings were started to be collated in 1944. The highest all-time seasonal rainfall was recorded at 3,759.7 mm in 1958 .
The official four months of the monsoon season ended just 70 mm short of the all-time record this year.
Maximum rainfall was recorded in July at 1,502.7mm -- the highest since 1944 -- followed by the highest in August at 1,247.6mm since 1959.
However, June recorded the lowest rainfall in five years at 395 mm.
But in September, 60% of excess rainfall was recorded at 549.1 mm.
Mumbai recorded the second-highest October rainfall in 10 years at 170.1 mm -- 27.6 mm short of the decades’ monthly high of 197.7 mm that was recorded in 2012.
Mumbai and Maharashtra recorded 67% and 16% of excess rainfall, respectively, between June and September.
Mumbai and Maharashtra recorded 103% and 75% of excess rainfall, respectively, from October 1 to October 28.
“Mumbai and Maharashtra have reported an exceptional performance as far as rainfall this monsoon is concerned. Now, it’s high time for the monsoon to withdraw,” Rajeevan added.