Southwest Monsoon 2021 has completed withdrawal from the entire country on 25thOctober. It shares the date with monsoon 2017. Most delayed withdrawal was in 2020 on 28th October. The withdrawal 2021 coincides with the onset of northeast monsoon over south India, as it also happened last year in 2020.
Normal date of onset of monsoon over mainland is 01stJune and withdrawal from the last post is taken as 15thOctober. This year the onset was on 03rdJune and final exit on 25thOctober, making it a duration of 145 days. Irrespective of early onset or late withdrawal, the seasonal rainfall is limited to 4 months and the records get closed on 30thSeptember.
Active monsoon period is the shortest for the state of Rajasthan (nearly 2 months) and complete 4 months for the central and eastern parts of the country. A total of 880.6mm rainfall (LPA) is realized during the season, with July and August as core monsoon months delivering rains over all parts of the country.
Withdrawal of monsoon need to satisfy a set of criterion including rainfall activity ceases over the area for 5 consecutive days, reversal in the wind pattern with establishment of anticyclone, moisture content to reduce as inferred from water vapour imageries.
Between 1960 & 2021, the earliest of monsoon withdrawal was 23rd September 1963 and the most delayed on 28th October 2020. The pattern of monsoon withdrawal is somewhat skewed wherein Before 30 September- the withdrawal was seen 8 times, Between 01-05 October - 11 times, Between 06-10 October - 17 times, Between 11-15 October - 16 times and between 16-28 October - 8 times
It is very evident from the data, that on more than 50% of the occasions, the withdrawal took place between 06th and 15th October. However, it seems as if the withdrawal is getting further delayed in the recent times. Since 2011, the earliest withdrawal was October 16, in 2019 and the most delayed on October 28, in 2020 :
The commencement of withdrawal from West Rajasthan in the last 6 years was earliest in 2016 (16 September) and most delayed in 2019 (09 October). The earliest onset during this period was in 2018(29 May) and the most delayed in 2016( 08June).