The India Meteorological Department (IMD) has predicted that the southwest monsoon is likely to hit Kerala on May 27, marking an early arrival compared to the normal onset date of June 1. 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% of the long-period average (LPA) of 87 cm -- within a model error margin of 5%. This forecast also indicates a minimal impact of El Nino conditions, which typically reduce rainfall in the Indian subcontinent.
Rainfall between 96% and 104% of the LPA is considered normal. Rainfall below 90% is classified as deficient, between 90% and 95% as below normal, 105% to 110% as above normal, and more than 110% as excess.
The monsoon is critical for India’s agriculture sector, which supports over 42% of the population and contributes 18.2% to the national GDP. It also plays a vital role in replenishing water reservoirs essential for drinking water and hydroelectric power.