Middle of September, brings the southwest monsoon closer to the date of commencement of withdrawal process. As per normal records, monsoon starts its withdrawal from extreme western parts of Rajasthan from 17September. Within a window of 5 days, from 25th to 30th September, withdrawal gets completed from the state. During this period, monsoon also retreats from Kutch, Jammu & Kashmir, Ladakh, Himachal Pradesh, Punjab, Haryana and Delhi.
Monsoon onset and withdrawal dates were revised by the National Weather Service, in 2020. Based on data from 1961 to 2019, withdrawal dates were delayed by 7-14 days from different parts of the country. Earlier scheduled withdrawal of 01Sep from extreme West Rajasthan was revised to 17thSeptember. Final withdrawal date of 15 October from South Peninsula remained sacrosanct.
Despite revision of dates of withdrawal, monsoon does not seem to be keeping the timelines. Immediately after the revival year, the monsoon withdrawal got unduly delayed to 06 October in 2021, itself. Last year, of course, the delay was marginal and the process started on 20thSeptember. This year, it is likely to overshoot the timelines by more than a week.
Monsoon withdrawal normally gets completed in about 30days. But the process has occasionally been rather abrupt. In 2019, the most delayed withdrawal, commenced on 09thOctober and got completed by 17thOctober, taking merely 8 days. Withdrawal of monsoon from any region is generally retrospective, as the weather features need to be consistent for few days.
Monsoon withdrawal is not attempted before 01st September. The synoptic features which need to be considered for the first withdrawal from northwest India include the Cessation of rainfall activity over the area for 5 consecutive days, the Establishment of anticyclone in the lower levels of atmosphere and a considerable drop in humidity levels as inferred from water vapour imageries
These conditions are unlikely to be met for the next 10 days or even more. The well-marked low-pressure area over the Bay of Bengal will push its way, right up to West Madhya Pradesh and North Madhya Maharashtra. Rains may spill over from this system to cover South and East Rajasthan, intermittently, till 22nd-23rd September. Moist easterly winds will continue to sweep most parts of the state. Accordingly, withdrawal of monsoon may roll over to the last week of September.