Southwest monsoon over the Indian subcontinent is the largest global event spread over time and space. Though it largely impacts Asia and Africa, but also leaves indelible marks over other continents, albeit more prominently in the Northern Hemisphere. The four-month-long journey between June and September is flanked by the inner and outer wings of May and October. Monsoon has precedence of arriving as early as 18th May in 2004 and withdrawn as late as 28th October in 2020, overlapping with the onset of Northeast Monsoon.
The month of June is obsessed as a viral marker of Monsoon but factually it may not hold ground statistically. Firstly, the early or late arrival of monsoon has got a very little bearing on its overall performance. In 2004, Monsoon landed on mainland Kerala on 18th May, 2 weeks ahead of its normal date. The month of June clocked 100% rainfall of LPA (long period average). National Weather Agency predicted the ISMR (Indian Summer Monsoon Rainfall) to be 100% of LPA. However, the season ended with drought with an overall deficiency of 13.8%. In 1983, the Monsoon announced its arrival over Kerala on 13th June, with a delay of nearly 2 weeks. The month of June remained deficient by 16% rainfall but the season finished with a record excess of 12.6%.
In the recent past, seasonal rainfall found hardly any correlation with June performance. It is an opening month leading to phenomenal environmental changes, specially the oceans on either side of the Indian coastline. Continental and oceanic heat potential, the driving force behind the monsoon activity, changes drastically. The month of June accounts for the stabilization of these changes and is therefore susceptible to large variations in the rainfall pattern.
June 2021 has been an undulating month with large daily variations. For the 1st three weeks, daily rainfall generally remained above normal except on 2 days (07th and 08th) when it was deficient by 44% and 33% respectively. Monsoon advanced with a speedy pace covering 80% area in just 10days. Delhi missed an early arrival by a whisker and may observe substantial delay now. In the absence of any fresh monsoon system, the northern limit of monsoon (NLM) is stuck on the outskirts of Delhi and short of Punjab and Haryana.
Rainfall surplus had sustained above 30% during the 3rd week and even climbed to 41% on 19th and 20th June. The spurt in the monsoon activity has now dipped and is mostly confined to east and northeast India. The surplus rainfall got consumed in the 4th week and now the month of June has ended with a monthly total of 110% of LPA (Long Period Average). However, June rainfall need not be construed as any lead to the seasonal performance as such.