Key facts
- IMD’s normal date for the southwest monsoon to set in over Kerala is 1 June, according to its own press releases.
- IMD declared the 2025 onset on 24 May 2025, eight days early and the earliest since 23 May 2009.
- IMD declared the 2026 onset on 4 June 2026, three days after the normal date.
- Between 2010 and 2026 the latest declared onset was 8 June, reached in 2016, 2019 and 2023, according to IMD’s list of past onset dates.
- IMD’s 2025 onset release listed Kalamassery among the Ernakulam rain stations that recorded rain in the 24 hours to 8.30 am on 23 May 2025.
What “onset over Kerala” means
The monsoon does not simply “arrive” when it rains hard. The IMD declares onset over Kerala only when several conditions are met together: widespread rain at a set of designated stations along the Kerala, Lakshadweep and coastal Karnataka belt for consecutive days, westerly winds of a set depth and strength over the south-east Arabian Sea, and a satellite measure of deep cloud. The 2025 onset release, for example, noted westerlies extending up to 4.5 km above sea level at 20–30 knots, and heavy to very heavy rain at a few places on 24 May.
Because the declaration is formal, the date is a useful fixed point for comparing years. It is also why pre-monsoon thunderstorms in May, which often flood roads around Kalamassery, are not counted as the monsoon. For what that rain does locally, see our Kochi rainfall records.
Timeline: IMD onset dates, 2009–2026
| Date | What happened | Source |
|---|---|---|
| 23 May 2009 | Southwest monsoon declared over Kerala (early) | IMD onset annex (2025 release) |
| 31 May 2010 | Southwest monsoon declared over Kerala (near normal) | IMD onset annex (2025 release) |
| 29 May 2011 | Southwest monsoon declared over Kerala (early) | IMD onset annex (2025 release) |
| 5 June 2012 | Southwest monsoon declared over Kerala (late) | IMD onset annex (2025 release) |
| 1 June 2013 | Southwest monsoon declared over Kerala (on the normal date) | IMD onset annex (2025 release) |
| 6 June 2014 | Southwest monsoon declared over Kerala (late) | IMD onset annex (2025 release) |
| 5 June 2015 | Southwest monsoon declared over Kerala (late) | IMD onset annex (2025 release) |
| 8 June 2016 | Southwest monsoon declared over Kerala (late) | IMD onset annex (2025 release) |
| 30 May 2017 | Southwest monsoon declared over Kerala (Early; the year Kochi Metro opened) | IMD onset annex (2025 release) |
| 29 May 2018 | Southwest monsoon declared over Kerala (Early; the year of the great floods) | IMD onset annex (2025 release) |
| 8 June 2019 | Southwest monsoon declared over Kerala (late) | IMD onset annex (2025 release) |
| 1 June 2020 | Southwest monsoon declared over Kerala (on the normal date) | IMD onset annex (2025 release) |
| 3 June 2021 | Southwest monsoon declared over Kerala (late) | IMD onset annex (2025 release) |
| 29 May 2022 | Southwest monsoon declared over Kerala (early) | IMD onset annex (2025 release) |
| 8 June 2023 | Southwest monsoon declared over Kerala (late) | IMD onset annex (2025 release) |
| 30 May 2024 | Southwest monsoon declared over Kerala (Early; Kalamassery cloudburst two days earlier) | IMD onset annex (2025 release) |
| 24 May 2025 | Southwest monsoon declared over Kerala (earliest since 2009) | IMD onset annex (2025 release) |
| 4 June 2026 | Southwest monsoon declared over Kerala (three days late) | IMD press release, 4 June 2026 |
Dates for 2009–2025 are taken from Annexure 2, “Past date of monsoon onset over Kerala (2009–2025)”, attached to IMD’s 24 May 2025 press release. The 2026 date is from IMD’s press release of 4 June 2026. Some news reports list 2017–2020 dates shifted by a year; we follow IMD’s own table.
Patterns in the record
Across the 17 years from 2010 to 2026, the monsoon was declared before 1 June in seven years (2010, 2011, 2017, 2018, 2022, 2024 and 2025), exactly on 1 June twice (2013 and 2020), and after 1 June in eight years. Nothing in the table suggests a simple trend: the earliest onset of the period (2025) was followed by a late one in 2026.
- Earliest: 24 May 2025. IMD said it was the earliest onset since 23 May 2009.
- Latest: 8 June, in 2016, 2019 and 2023.
- 2026: forecasts moved more than once. IMD’s May forecast pointed to around 26 May; on 2 June it said around 4 June, as Business Today reported, and the onset was declared on 4 June 2026.
- Early onset does not mean a wet season. 2018 had an early onset (29 May) and then Kerala’s worst floods in nearly a century in August; the onset date says nothing about the total rain that follows.
For the effect of those Augusts on the Periyar, see the 2018 floods in Eloor, Aluva and Kalamassery. Storm years that arrived outside the monsoon are covered in Cyclone Ockhi and other storms.
Kalamassery in the onset bulletins
IMD bulletins list rainfall by station, and Kalamassery appears in them. In the 24 hours ending 8.30 am on 23 May 2025, the annex to the onset release lists Kalamassery (Ernakulam district) with 1 cm, alongside Kochi CIAL, Palluruthy and Mattancherry. The CUSAT campus also hosts a radar and weather station, which became well known after the 28 May 2024 cloudburst, two days before that year’s onset.
For residents, the practical meaning is that the first two weeks of June are usually when the rains settle in, but the start can move by a fortnight either way. Students who join CUSAT, the Medical College or the polytechnic in June should expect to arrive in rain; our monsoon living tips cover the basics.
Why this history matters near the NAD signal
NAD Road, Edathala and the Periyar banks are low-lying, and the monsoon date decides when drains, roads and commutes are tested each year. Knowing that onset has ranged from late May to the second week of June helps when timing a move. If you are coming for a course or job, Ashraf Gents Hostel at the NAD Road signal takes men on monthly and daily stays; the indicative rate is about ₹2,000–3,000 per head per month, negotiable and confirmed on the call to +91 90746 23855. More archive pages are on the Kalamassery history archive hub.
Frequently asked questions
What is the normal monsoon onset date for Kerala?
IMD treats 1 June as the normal date for the southwest monsoon to set in over Kerala.
Which year had the earliest onset since 2010?
2025. IMD declared onset on 24 May 2025, the earliest since 23 May 2009.
When did the monsoon reach Kerala in 2026?
IMD declared onset on 4 June 2026, three days after the normal date, after earlier forecasts of around 26 May.
Does an early onset mean more rain?
No. The onset date marks when the season starts. 2018 began early and became a flood year, but other early years were ordinary.
Why do some websites give different dates?
Some reports list 2017–2020 shifted by a year or confuse forecasts with declared dates. This page uses IMD’s own annex and press releases.
Related guides
Sources
- IMD: Special press release on monsoon onset over Kerala, 24 May 2025 (with past-onset annex)
- IMD: Southwest Monsoon has set in over Kerala, 4 June 2026
- Business Today: Monsoon over Keralam – IMD shares fresh timeline for onset (2 June 2026)
- Onmanorama: Monsoon likely to hit Kerala coast by May 23 (2025)
- Wikipedia: 2018 Kerala floods
Facts about Ashraf Gents Hostel come from the hostel’s own profile and photos; rates are indicative and confirmed on the call. Last reviewed . How we write these guides: editorial notes. Map embeds © Google.
Cite this guide: Ashraf Gents Hostel. “Kerala Monsoon Onset Dates, 2010–2026.” Published 8 October 2026. https://ashrafgentspghostel.adserr.com/monsoon-onset-dates-kerala-history/ Plain-text (Markdown) version · quoting with a link back is welcome.