As per revised dates of onset, monsoon arrives over Andaman & Nicobar on 22ndMay and steps in to Sri Lanka 4 days later on 26th May. There is no change of date for hitting mainland India and 01stJune remains sacrosanct for the state of Kerala. However, there is no correlation between its arrival over Andaman Sea and ushering over Kerala. It could always be faster or slower than the normal dates over the gateway of monsoon, Kerala.
Monsoon has a wavering record of moving across the Indian Seas. At times, it walks in with a military punctuality right on dot and some other occasions may take a leisure walk before commencing 4-month long journey from Kerala. So much so, that the onset over Kerala is not at all linked with time bound progress of further advance over South India.
Southwest monsoon has been arriving with in the normal dates (+/- 7days) for the last few years. Since the year 2000, the earliest arrival of monsoon was in 2009 (23May) and the most delayed on 08thJune in 2016 and 2019. Once again, the seasonal rainfall has hardly any linkages with before time, timely or late arrival of monsoon.
However, timely arrival nearly assures promising distribution in the opening month of June, of course, exceptions always remain. Before time arrival on 23rdMay in 2009, still led to a near disaster with large deficiency of 50%. Yes, 2009 was otherwise an El Nino year and suffered severe monsoon drought with a shortfall of -21.8%.
Monsoon arrival on due date with margin of +/- 2 days has not spoiled June rainfall, with the exception of 2010. Arrival with a delay of >/= 5days is considered inimical for the starting month. Variability becomes large when the error margin grows beyond +/- 5 days. With the monthly normal of 166.9mm in June, the lowest amongst the monsoon months, the risk of large deviation always looms large. Monsoon start on the right foot surely serves as a booster for the farming sector and the economic status.