September is one of the warmer months of the year in Merton, with average highs near 19.5°C and lows around 10.1°C (mean 14.8°C). It is about average for rainfall, averaging 54 mm of rainfall and 81% relative humidity across the period.
September is one of the warmer months of the year in Merton. Across 45 years of records, the warmest September in Merton was 2023 — when the month averaged 18.4°C — while the coldest was 1986 at 11.9°C. Typical September days reach 19.5°C with nights near 10.1°C. The long-term trend is warming, about 0.4°C per decade.
September is about average for rainfall in Merton, averaging 54 mm of rainfall. The wettest September on record was 2000 with 107 mm, while the driest was 1997 at 15 mm.
Relative humidity in Merton during September averages 81%. The most humid September was 2000 at 86%, and the least humid was 1990 at 73%.
September receives about 3.2 kWh/m²/day of solar energy in Merton. The sunniest September was 1991 at 3.6 kWh/m²/day, and the cloudiest was 2000 at 2.6.
Average wind speed in Merton during September is 3.2 m/s. The windiest Septembers were 1983 and 2025 at 3.9 m/s, while the calmest were 2003 and 2014 at 2.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 14.3°C | 14.4°C | 15.1°C | 14.7°C | 16.0°C | +1.7°C |
| Avg High | 19.0°C | 18.9°C | 19.7°C | 19.6°C | 20.9°C | +1.9°C |
| Avg Low | 9.7°C | 9.8°C | 10.4°C | 9.9°C | 11.2°C | +1.5°C |
| Avg Rain | 51 mm | 69 mm | 49 mm | 47 mm | 54 mm | +2 mm |
September temperatures in Merton have risen by about 1.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 2.5°C (2003) to a record high of 31.1°C (2023).
Rainfall in September is about average for rainfall, averaging 54 mm, with a wettest year of 107 mm.
One of the best times to visit Merton
September is one of the best times to visit Merton. Expect days averaging 19.5°C and nights around 10.1°C (mean 14.8°C) — warmer than Merton's yearly average — with moderate rainfall (54 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 20.2°C | 15.3°C | 10.4°C | 26.7°C | 5.4°C | 43 mm | 77% | 3.9 m/s | 3.4 |
| 2024 | 19.7°C | 15.3°C | 10.8°C | 27.0°C | 4.4°C | 91 mm | 83% | 3.2 m/s | 2.9 |
| 2023 🔥 | 23.4°C | 18.4°C | 13.4°C | 31.1°C | 8.0°C | 41 mm | 80% | 2.8 m/s | 3.3 |
| 2022 | 20.1°C | 15.4°C | 10.8°C | 25.2°C | 5.1°C | 58 mm | 78% | 2.8 m/s | 3 |
| 2021 | 21.4°C | 16.5°C | 11.6°C | 27.2°C | 5.9°C | 46 mm | 83% | 2.7 m/s | 3.2 |
| 2020 | 20.6°C | 15.3°C | 10.1°C | 26.7°C | 5.1°C | 44 mm | 77% | 3.3 m/s | 3.5 |
| 2019 | 20.3°C | 15.1°C | 10.0°C | 25.5°C | 5.7°C | 76 mm | 78% | 3.5 m/s | 3.4 |
| 2018 | 19.9°C | 14.7°C | 9.5°C | 24.2°C | 4.2°C | 38 mm | 76% | 3.3 m/s | 3.4 |
| 2017 | 18.7°C | 14.0°C | 9.4°C | 22.8°C | 5.1°C | 56 mm | 82% | 3.2 m/s | 2.9 |
| 2016 | 21.5°C | 16.7°C | 11.9°C | 27.9°C | 6.4°C | 34 mm | 82% | 3.1 m/s | 3 |
| 2015 | 17.5°C | 12.9°C | 8.3°C | 20.2°C | 4.9°C | 55 mm | 83% | 2.9 m/s | 3.4 |
| 2014 | 20.8°C | 15.9°C | 10.9°C | 23.0°C | 6.0°C | 17 mm | 83% | 2.2 m/s | 3.2 |
| 2013 | 19.0°C | 14.3°C | 9.5°C | 27.9°C | 5.6°C | 49 mm | 83% | 2.7 m/s | 2.9 |
| 2012 | 18.5°C | 13.6°C | 8.6°C | 25.8°C | 4.4°C | 52 mm | 80% | 3.2 m/s | 3.5 |
| 2011 | 20.8°C | 15.9°C | 11.0°C | 26.6°C | 7.7°C | 36 mm | 81% | 3.7 m/s | 3.3 |
| 2010 | 18.5°C | 14.1°C | 9.6°C | 22.8°C | 4.2°C | 54 mm | 83% | 3.3 m/s | 3 |
| 2009 | 20.1°C | 15.3°C | 10.5°C | 24.5°C | 7.8°C | 25 mm | 78% | 3.4 m/s | 3.4 |
| 2008 | 18.3°C | 14.0°C | 9.8°C | 22.1°C | 6.7°C | 55 mm | 81% | 3.2 m/s | 2.9 |
| 2007 | 19.2°C | 14.4°C | 9.5°C | 23.7°C | 5.5°C | 26 mm | 81% | 3.2 m/s | 3.3 |
| 2006 | 22.5°C | 17.7°C | 13.0°C | 27.5°C | 8.2°C | 70 mm | 81% | 3.2 m/s | 3.4 |
| 2005 | 21.1°C | 16.1°C | 11.0°C | 26.8°C | 4.2°C | 51 mm | 81% | 2.8 m/s | 3.3 |
| 2004 | 19.9°C | 15.2°C | 10.5°C | 25.9°C | 4.8°C | 26 mm | 81% | 3.8 m/s | 3.4 |
| 2003 | 20.4°C | 14.8°C | 9.1°C | 25.2°C | 2.5°C | 17 mm | 78% | 2.2 m/s | 3.5 |
| 2002 | 19.0°C | 14.5°C | 10.0°C | 22.1°C | 7.4°C | 39 mm | 82% | 2.7 m/s | 3.3 |
| 2001 | 17.4°C | 13.3°C | 9.2°C | 21.3°C | 7.0°C | 71 mm | 84% | 3.6 m/s | 2.8 |
| 2000 🌧️ | 19.4°C | 15.2°C | 11.1°C | 25.5°C | 6.1°C | 107 mm | 86% | 3.2 m/s | 2.6 |
| 1999 | 20.4°C | 16.2°C | 11.9°C | 27.1°C | 9.1°C | 100 mm | 85% | 3.2 m/s | 3.2 |
| 1998 | 19.5°C | 15.2°C | 11.0°C | 23.5°C | 6.5°C | 103 mm | 84% | 3.4 m/s | 3.1 |
| 1997 | 19.9°C | 15.1°C | 10.2°C | 24.2°C | 6.2°C | 15 mm | 80% | 2.9 m/s | 3.4 |
| 1996 | 18.3°C | 13.8°C | 9.4°C | 21.8°C | 6.4°C | 29 mm | 79% | 3.4 m/s | 3.1 |
| 1995 | 18.2°C | 13.8°C | 9.4°C | 21.0°C | 4.7°C | 105 mm | 81% | 3.2 m/s | 3 |
| 1994 | 17.1°C | 13.1°C | 9.0°C | 20.6°C | 5.2°C | 83 mm | 84% | 3.4 m/s | 2.9 |
| 1993 | 16.8°C | 12.6°C | 8.4°C | 21.5°C | 5.7°C | 95 mm | 84% | 3.1 m/s | 2.7 |
| 1992 | 18.4°C | 13.8°C | 9.2°C | 22.7°C | 5.3°C | 82 mm | 84% | 3.3 m/s | 3.1 |
| 1991 | 21.3°C | 15.9°C | 10.4°C | 27.4°C | 5.7°C | 44 mm | 76% | 2.8 m/s | 3.6 |
| 1990 | 19.2°C | 14.1°C | 9.0°C | 25.8°C | 5.8°C | 36 mm | 73% | 3.2 m/s | 3.1 |
| 1989 | 20.5°C | 16.0°C | 11.4°C | 25.6°C | 7.7°C | 32 mm | 78% | 3.2 m/s | 3 |
| 1988 | 18.4°C | 13.9°C | 9.5°C | 23.4°C | 3.0°C | 54 mm | 82% | 3.7 m/s | 2.8 |
| 1987 | 18.8°C | 14.2°C | 9.7°C | 24.5°C | 3.8°C | 41 mm | 83% | 3 m/s | 3 |
| 1986 ❄️ | 16.9°C | 11.9°C | 7.0°C | 20.6°C | 3.6°C | 34 mm | 80% | 2.6 m/s | 3.4 |
| 1985 | 19.8°C | 14.9°C | 10.0°C | 25.4°C | 5.0°C | 19 mm | 82% | 3 m/s | 3.3 |
| 1984 | 18.2°C | 13.9°C | 9.6°C | 25.0°C | 6.1°C | 68 mm | 80% | 3.6 m/s | 2.9 |
| 1983 | 18.5°C | 14.1°C | 9.7°C | 24.1°C | 5.3°C | 63 mm | 82% | 3.9 m/s | — |
| 1982 | 20.3°C | 15.2°C | 10.0°C | 26.2°C | 6.3°C | 59 mm | 83% | 2.8 m/s | — |
| 1981 | 19.4°C | 15.0°C | 10.7°C | 24.7°C | 6.4°C | 92 mm | 82% | 3.3 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 19.5°C with lows near 10.1°C (mean 14.8°C), based on 45 years of NASA POWER data.
September averages 54 mm of rainfall in Merton, about average for rainfall. The wettest on record was 107 mm in 2000.
The hottest September reached 31.1°C in 2023. The coldest dipped to 2.5°C in 2003.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.6°C. Daytime highs moved from 19.2°C to 21°C and overnight lows from 10°C to 11.4°C over the same span.
September is one of the warmer months of the year in Merton and about average for rainfall, so plan for around 19.5°C daytime highs and 10.1°C at night.
Not quite — September is the 9th coolest month in Merton, averaging 14.8°C.
For September in Merton, pack light layers you can adjust through the day, with typical highs of 19.5°C and lows of 10.1°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 81% — quite humid.
Average wind speed in September is 3.2 m/s. The windiest September on record averaged 3.9 m/s (1983).
The wettest September on record was 2000 with 107 mm. On average, September sees 54 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Merton behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
