Southwest monsoon likely to hit Kerala by May 27, says IMD

If the forecast holds, it would be the earliest monsoon onset over the Indian mainland since 2009, when it arrived on May 23.

The arrival of the monsoon in Kerala signals the beginning of the country’s primary rainy season, which typically extends from June to September.

The IMD formally declares the onset of the monsoon once specific meteorological conditions are met over the southern state. From there, the monsoon generally spreads across the entire country by July 8, begins retreating from northwest India around September 17, and withdraws fully by October 15.

In recent years, the onset dates have varied. The monsoon reached Kerala on May 30 last year, on June 8 in 2023, May 29 in 2022, June 3 in 2021, and June 1 in 2020. In 2019, it arrived on June 8, while in 2018, it set in on May 29.

An IMD official clarified that the timing of the monsoon’s arrival in Kerala does not directly correlate with the total rainfall expected during the season across the country.

“An early or late onset over Kerala doesn’t necessarily mean the same for the rest of India. The monsoon system is influenced by large-scale atmospheric dynamics and regional weather patterns,” the official said.

The IMD had earlier forecast above-normal cumulative rainfall for the 2025 southwest monsoon season, with rainfall expected to be around 105 per cent of the long-period average (LPA) of 87 cm -- within a model error margin of five per cent.

This forecast also indicates a minimal impact of El Nino conditions, which typically reduce rainfall in the Indian subcontinent.

Rainfall between 96 per cent and 104 per cent of the LPA (Long Period Average) is considered normal. Rainfall below 90 per cent is classified as deficient, between 90 per cent and 95 per cent as below normal, 105 to 110 per cent as above normal, and more than 110 per cent as excess.

The monsoon is critical for India’s agriculture sector, which supports over 42 per cent of the population and contributes 18.2 per cent to the national GDP. It also plays a vital role in replenishing water reservoirs essential for drinking water and hydroelectric power.