The southwest monsoon set in over Kerala on Saturday, slightly ahead of the normal June 1 onset. It is the earliest monsoon onset on the Indian mainland since 2009, when it began on May 23.
In recent years, the monsoon reached Kerala on May 30 in 2023, June 8 in 2022, May 29 in 2021, June 3 in 2020, June 1 in 2019, June 8 in 2018, and May 29 in 2017. However, experts caution that an early onset does not always ensure steady or well-distributed rainfall. It can sometimes signal delays in monsoon progression across the rest of the country and erratic rainfall patterns.
According to a research paper from the Indian National Centre for Ocean Information Services (INCOIS) by P A Francis and Sulochana Gadgil, the 2009 monsoon—despite its early onset—began with a 48% rainfall deficit across India in June. While July rainfall that year was close to normal, August saw a deficit of 27%. Notably, the broader climate conditions in 2009, including the El Nino–Southern Oscillation (ENSO) and the equatorial Indian Ocean Oscillation, were unfavourable.
“We have predicted an above-normal monsoon this time. The variability and distribution of the monsoon depend on multiple factors that develop throughout the season,” said Neetha K Gopal, IMD Director for the Kerala region.
According to the IMD’s long-range forecast, the southwest monsoon is expected to be above normal, with seasonal rainfall likely to reach 105% of the Long Period Average (LPA) with a margin of ±5%.
“Monsoon progression is rarely uniform- it moves forward in phases. Following the onset, we expect a good amount of rain in the last week of May. However, rainfall may decrease in the first week of June. Precipitation is likely to pick up again once conditions become favourable,” she added.
A key influence on the Indian monsoon is the El Nino–Southern Oscillation (ENSO). This year, ENSO conditions are neutral—typically a good sign for monsoon performance.
Speaking on Onmanorama’s podcast News Brake, Dr Sinan Nisar, junior scientist at the Institute of Climate Change Studies (ICCS), Kottayam, said that “Though the correlation between El Nino and Kerala’s rainfall isn’t always strong, neutral conditions are promising,” Dr Nisar explained. “We are also seeing favourable signals from other teleconnections like the Indian Ocean Dipole and Eurasian snow cover, which should support monsoon strength.” In climate science, teleconnections refer to links between weather patterns or climate anomalies occurring far apart across the globe.
At present, neutral Indian Ocean Dipole (IOD) conditions are prevailing, and the latest climate models suggest these are likely to continue through the monsoon season. Another encouraging sign is the below-normal snow cover observed in the Northern Hemisphere and Eurasia during January–March 2025—typically associated with stronger Indian summer monsoons.
Yet even if the total rainfall falls within the normal range, climate change drives higher variability in how that rain is distributed. According to Dr Nisar, recent years have increased extreme rainfall events (EREs), marked by short but intense downpours and longer dry spells.
“The same total rainfall may now fall over fewer days, in more intense bursts—this is the hallmark of climate-induced variability,” Dr Nisar said. “Such extreme rainfall events are likely to increase this year.”
While the IMD’s seasonal forecasts have become significantly more reliable since the early 2000s, short-term forecasts—critical for local disaster preparedness—remain challenging in Kerala due to its complex topography and sparse observation infrastructure.
“Kerala has highly localised rainfall patterns, and we need a denser network of observation stations to improve short-term accuracy. To address this gap, new radar stations are being installed, and collaborative efforts are underway between the IMD, ICCS, and the state government to expand the data-gathering network,” Dr Nisar noted.
As extreme weather events become more frequent, better coordination between weather data agencies is also essential. ICCS is developing a mobile app to consolidate temperature and rainfall data from multiple sources.
“Right now, there’s no common platform for observational data,” Dr Nisar said. “This app will help screen and standardise information so that agencies like IMD and ICCS can use it for more accurate and timely forecasts.” The app is expected to launch by mid-monsoon.