Across the 34 years of record to 2024, the monsoon's first sustained rain reaches Mumbai around 4 June on average. That is an average, not a forecast for this year.
In half of those years it arrived between 1 June and 8 June. That 7-day window is the number worth planning around. Mumbai is one of the more dependable places in this respect — the date moves, but not far.
Why this differs from the official date
IMD puts the normal onset of the monsoon over Mumbai at about 11 June. Our figure is around a week earlier, and the gap is not noise - it is what the two are measuring. IMD declares onset for a city only once the large-scale monsoon circulation has established over it, using wind and outgoing-radiation fields as well as rain. We look only at rainfall, and on the Konkan coast the pre-monsoon showers that arrive with the first onshore winds are already heavy and persistent enough to satisfy our test. Both dates are correct answers to different questions: ours asks when the sustained rain starts, IMD asks when the monsoon has arrived.
The full range is much wider: earliest 13 May 2000, latest 19 June 2009 — 37 days apart.
Common questions about the monsoon in Mumbai
When will the monsoon reach Mumbai?
Around 4 June on average, and between 1 June and 8 June in half of years. The exact date in any single year cannot be known in advance; the window can.
When does it rain in Mumbai?
94% of the 1977 mm this city receives in a year falls between June and September. July is the wettest month — 687 mm across about 31 days of rain.
How long does the monsoon last in Mumbai?
About 138 days, with withdrawal around 17 October.
What changes when it arrives
The clearest change is heat. April averages a daily maximum of 32.8°C; by July that has fallen 4.9°C. Rain days rise too: roughly 111 days of rain across June to September.
The last 12 years
This is Mumbai's own record, not a regional average.
| Year | Monsoon onset | Withdrawal | Days |
|---|---|---|---|
| 2013 | 31 May | 15 October | 137 |
| 2014 | 11 June | 21 September | 102 |
| 2015 | 6 June | 13 October | 129 |
| 2016 | 9 June | 13 October | 126 |
| 2017 | 28 May | 9 December | 195 |
| 2018 | 3 June | 29 September | 118 |
| 2019 | 8 June | 10 November | 155 |
| 2020 | 30 May | 31 October | 154 |
| 2021 | 13 May | 9 December | 210 |
| 2022 | 6 June | 26 October | 142 |
| 2023 | 9 June | 9 October | 122 |
| 2024 | 4 June | 30 October | 148 |
Where these numbers come from
Source: Open-Meteo's historical weather archive, whose default model blends ERA5 and ERA5-Land reanalysis with ECMWF IFS HRES from 2017 — 1991-2024 (34 years). Open-Meteo offers no rainfall from ERA5-Land, so the rain figures come from ERA5 and IFS. Temperatures are monthly averages of daily highs and lows; rainfall is the average monthly total. A grid estimate can differ from a local weather station. The grid point used for Mumbai sits about 3 km from the city. Onset dates are worked out from the same source's daily rainfall.
Our definition of onset is the first day on or after 1 May on which the five days starting that day bring at least 20 mm of rain, the ten days after those bring at least 30 mm, and each of the three ten-day periods starting that day brings at least 20 mm. The last condition is there to screen out cyclones; it was added after an earlier version of the rule recorded cyclone Tauktae, in May 2021, as the monsoon's arrival in four cities hundreds of kilometres apart. It narrows that problem without removing it: where a cyclone's rain runs straight into a wet June, the rule can still return a May date. Withdrawal is the last day of the last ten-day period, starting between 1 June and 30 November, that brings at least 20 mm.