Bengaluru: In a significant development, the India Meteorological Department (IMD) has forecast that the southwest monsoon is likely to make an early onset over Kerala on May 27, five days ahead of the normal date of June 1. If the forecast holds true, it will be the earliest onset since 2009, when the monsoon arrived on May 23.

“The conditions are becoming favourable for the onset of monsoon over Kerala around May 27,” the IMD said on Monday.

A timely and strong monsoon onset is considered crucial for agricultural planning, water reservoir replenishment, and early sowing in rain-fed regions.

The average monsoon onset date over Kerala is June 1, with a standard deviation of about ±7 days. However, such early arrivals are rare. In the last 15 years, only two instances of May arrivals have been recorded: in 2009 (May 23) and 2018 (May 29).

Once the monsoon sets over Kerala, it typically covers the entire Indian mainland by around July 8, progressing northward in phases. It begins to retreat from north-western India around September 17, and usually withdraws fully by October 15.