Southwest monsoon 2021 is likely to commence withdrawal, tentatively from 06th October. Possibly, it is going to be rapid retreat from entire northwest India, both hills and plains. It may linger on for another one week or more over central and eastern parts, covering Gujarat, Madhya Pradesh and Maharashtra (including Mumbai).
In view of the likely establishment of anticyclone circulation in the lower tropospheric levels over western parts of Northwest India and commensurate reduction in the moisture and rainfall, southwest monsoon is expected to withdraw from most parts of Rajasthan, Punjab, Haryana and the northern hilly states.
The mercury already has started shooting and crossed even 38°C at Ganganagar. National capital Delhi has also crossed 36°C. However, the humidity level is still high and awaits complete reversal of winds to drop below the threshold markers.
The country has witnessed an extended monsoon spell on account of increased rainfall over north India, in the last lap. It never showed any signs of retreat till fag end of September. Month of September was the 2nd wettest since 1983 as it ended with a huge surplus of 35% of long period average.
September 2019 remains the highest, with over 70years record of 52% surplus. During 2019, southwest monsoon also holds a record of being ‘most delayed’ withdrawal which commenced on 09thOctober, albeit also became the ‘quickest’ to get completed in just one week.
Prior to 2019, the normal date of start of withdrawal from West Rajasthan was considered as 01stSeptember. This date got revised to 17thSeptember, based on withdrawal data from 1971 to 2019.
Retreat of monsoon from most other parts also got revised and delayed by 7-14 days, from the then existing dates. However, final withdrawal date of 15thOctober from South Peninsula remained sacrosanct in view of likely onset of Northeast Monsoon anytime around 20thOctober.
As per existing criteria, if after 17thSep, rainfall ceases in an area for continuous 5days in northwest India; there is an establishment anticyclone in the atmosphere at about 5000’ above mean sea level and considerable reduction in moisture content as inferred from the water vapour imageries (satellite picture), then the 1st withdrawal of the monsoon is announced. Withdrawal of monsoon from a region may not be construed as complete absence of rain for a long period.