Monsoon in India is more than a seasonal phenomenon. Everything is hinged on these rains, from economic growth to farmers' fate and even spiritual well-being. This annual feature drenches Africa, Australia and Asia but it is on the Indian sub-continent that the monsoon casts a spell. It comes calling in early June and spreads across the landmass taking more than one month. It is also truant in nature, knocking sometimes with absolute punctuality or may even leave anxious moments for everyone by delaying arrival. Monsoon remains unpredictable in behaviour and decoding remains a challenge, year after year.
The onset date of the monsoon is more of academic interest as it does not find any connection with seasonal performance. Arrival date has an even poor relationship with its progress, pace and intensity. While a delayed arrival may catch up quickly to make rapid advancement along and off the coast, an early onset does not assure timely monsoon bursts. Monsoon, off late, is found to be in the habit of languishing over some part or the other of our country during the onset month of June.
Southwest monsoon arrived as early as on 18 May 2004 and delayed its landing to 18th June 1972. Incidentally, both these years ended up with drought. Monsoon season finished with a big surplus of 13% rainfall in 1983 despite starting its mainland journey on 13th June. As such, based on long-period data, the onset of monsoon has a standard deviation of one week. On more than 95% of the occasions, the arrival date strikes between 25th May and 08th June which is discreetly considered as normal.
The onset date of monsoon does not have a strong correlation with June rainfall. Last year, the monsoon arrived on 29th May and left the month of June with a shortfall of 8%. The year prior to that in 2020, the monsoon touched down on 03rd June and dumped 18% excess rainfall during the onset month. The pace and progress of monsoon after onset matter more than being sacrosanct of its normal date of 01st June.