September is one of the cooler months of the year in Horsham, with average highs near 17.6°C and lows around 5.5°C (mean 11.6°C). It is about average for rainfall, averaging 45 mm of rainfall and 75% relative humidity across the period.
September is one of the cooler months of the year in Horsham. Across 45 years of records, the warmest September in Horsham was 2023 — when the month averaged 13.6°C — while the coldest was 1992 at 9.1°C. Typical September days reach 17.6°C with nights near 5.5°C. The long-term trend is warming, about 0.2°C per decade.
September is about average for rainfall in Horsham, averaging 45 mm of rainfall. The wettest September on record was 2016 with 117 mm, while the driest was 1987 at 14 mm.
Relative humidity in Horsham during September averages 75%. The most humid September was 1992 at 84%, and the least humid was 1982 at 61%.
September receives about 4.5 kWh/m²/day of solar energy in Horsham. The sunniest September was 2023 at 5.1 kWh/m²/day, and the cloudiest were 2016 and 2022 at 4.
Average wind speed in Horsham during September is 2.9 m/s. The windiest September was 1996 at 3.7 m/s, while the calmest was 1997 at 2.3 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 11.2°C | 11.1°C | 11.9°C | 11.6°C | 12.1°C | +0.9°C |
| Avg High | 17.3°C | 17.0°C | 18.2°C | 17.8°C | 18.2°C | +0.9°C |
| Avg Low | 5.1°C | 5.2°C | 5.6°C | 5.5°C | 6.1°C | +1°C |
| Avg Rain | 41 mm | 53 mm | 41 mm | 44 mm | 46 mm | +5 mm |
September temperatures in Horsham have risen by about 1.1°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -0.4°C (1995) to a record high of 30.7°C (1987).
Rainfall in September is about average for rainfall, averaging 45 mm, with a wettest year of 117 mm.
A quieter season to visit Horsham
If your dates are flexible, the more temperate months of February and January tend to be the most comfortable for visiting Horsham. That said, September — with days averaging 17.6°C and nights around 5.5°C (mean 11.6°C) and moderate rainfall (45 mm) — can still be rewarding for travellers who don't mind the cooler conditions, and often means fewer crowds.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 18.0°C | 12.0°C | 6.1°C | 24.5°C | 0.2°C | 31 mm | 73% | 3.2 m/s | 4.4 |
| 2024 | 18.8°C | 12.4°C | 6.0°C | 26.3°C | 1.1°C | 43 mm | 70% | 3.3 m/s | 4.5 |
| 2023 🔥 | 20.7°C | 13.6°C | 6.5°C | 29.2°C | 1.8°C | 16 mm | 68% | 2.5 m/s | 5.1 |
| 2022 | 16.3°C | 11.1°C | 5.8°C | 20.2°C | 1.6°C | 71 mm | 81% | 2.8 m/s | 4 |
| 2021 | 17.5°C | 11.6°C | 5.8°C | 25.4°C | 1.2°C | 56 mm | 76% | 2.9 m/s | 4.5 |
| 2020 | 17.6°C | 11.9°C | 6.2°C | 24.0°C | 0.8°C | 59 mm | 76% | 3.1 m/s | 4.4 |
| 2019 | 17.2°C | 10.9°C | 4.6°C | 25.1°C | 0.4°C | 35 mm | 74% | 2.6 m/s | 4.7 |
| 2018 | 17.4°C | 10.6°C | 3.9°C | 24.4°C | 0.8°C | 14 mm | 71% | 2.7 m/s | 5 |
| 2017 | 17.0°C | 11.3°C | 5.5°C | 25.9°C | 1.5°C | 43 mm | 73% | 3.4 m/s | 4.6 |
| 2016 🌧️ | 16.1°C | 10.8°C | 5.4°C | 22.4°C | 2.7°C | 117 mm | 81% | 2.7 m/s | 4 |
| 2015 | 18.9°C | 12.1°C | 5.2°C | 28.4°C | 1.5°C | 32 mm | 69% | 2.5 m/s | 4.6 |
| 2014 | 19.3°C | 12.7°C | 6.0°C | 29.0°C | 2.0°C | 20 mm | 70% | 2.8 m/s | 4.8 |
| 2013 | 18.9°C | 13.2°C | 7.6°C | 24.9°C | 3.6°C | 59 mm | 78% | 3.1 m/s | 4.1 |
| 2012 | 18.4°C | 12.1°C | 5.8°C | 27.1°C | 2.1°C | 34 mm | 71% | 3 m/s | 4.4 |
| 2011 | 18.9°C | 12.3°C | 5.8°C | 28.4°C | 1.1°C | 30 mm | 71% | 3 m/s | 4.6 |
| 2010 | 15.5°C | 10.2°C | 4.9°C | 18.1°C | 1.4°C | 55 mm | 82% | 2.6 m/s | 4.2 |
| 2009 | 18.1°C | 11.9°C | 5.7°C | 27.8°C | 2.9°C | 63 mm | 73% | 3.2 m/s | 4.2 |
| 2008 | 18.2°C | 11.7°C | 5.2°C | 28.7°C | 1.7°C | 23 mm | 70% | 2.9 m/s | 4.8 |
| 2007 | 18.7°C | 12.1°C | 5.5°C | 25.2°C | 2.4°C | 24 mm | 68% | 3.3 m/s | 4.6 |
| 2006 | 20.0°C | 12.7°C | 5.5°C | 29.1°C | 1.3°C | 32 mm | 64% | 3 m/s | 4.8 |
| 2005 | 18.0°C | 12.1°C | 6.2°C | 25.8°C | 2.1°C | 37 mm | 73% | 2.7 m/s | 4.1 |
| 2004 | 17.2°C | 11.4°C | 5.7°C | 27.5°C | 2.2°C | 40 mm | 78% | 2.5 m/s | 4.1 |
| 2003 | 16.2°C | 10.4°C | 4.6°C | 25.3°C | 0.3°C | 32 mm | 78% | 3.5 m/s | 4.5 |
| 2002 | 18.8°C | 12.0°C | 5.2°C | 27.1°C | 0.2°C | 31 mm | 65% | 3.5 m/s | 4.4 |
| 2001 | 19.2°C | 12.9°C | 6.6°C | 29.4°C | 1.5°C | 68 mm | 74% | 2.8 m/s | 4.2 |
| 2000 | 17.7°C | 11.9°C | 6.2°C | 24.3°C | 3.0°C | 62 mm | 79% | 3.3 m/s | 4.3 |
| 1999 | 19.4°C | 13.0°C | 6.5°C | 27.4°C | 1.6°C | 25 mm | 71% | 2.8 m/s | 4.6 |
| 1998 | 19.0°C | 12.7°C | 6.3°C | 27.2°C | 2.2°C | 43 mm | 75% | 3.1 m/s | 4.5 |
| 1997 | 17.4°C | 11.4°C | 5.5°C | 20.6°C | 1.8°C | 83 mm | 77% | 2.3 m/s | 4.6 |
| 1996 | 15.6°C | 10.3°C | 4.9°C | 24.4°C | -0.1°C | 90 mm | 78% | 3.7 m/s | 4.3 |
| 1995 | 16.5°C | 10.6°C | 4.7°C | 21.9°C | -0.4°C | 21 mm | 79% | 2.6 m/s | 4.4 |
| 1994 | 16.4°C | 9.9°C | 3.5°C | 22.7°C | 0.0°C | 19 mm | 71% | 2.9 m/s | 4.4 |
| 1993 | 17.3°C | 11.6°C | 5.9°C | 26.6°C | 0.8°C | 74 mm | 78% | 2.9 m/s | 4.3 |
| 1992 ❄️ | 14.1°C | 9.1°C | 4.0°C | 16.7°C | 0.7°C | 91 mm | 84% | 2.6 m/s | 4.1 |
| 1991 | 16.1°C | 10.7°C | 5.2°C | 20.6°C | 1.4°C | 64 mm | 81% | 3 m/s | 4.5 |
| 1990 | 17.9°C | 11.8°C | 5.6°C | 26.7°C | 1.5°C | 24 mm | 74% | 3 m/s | 4.7 |
| 1989 | 16.8°C | 10.8°C | 4.7°C | 23.7°C | 2.4°C | 41 mm | 79% | 2.9 m/s | 4.7 |
| 1988 | 18.0°C | 11.9°C | 5.9°C | 24.7°C | 1.1°C | 71 mm | 76% | 2.9 m/s | 4.3 |
| 1987 | 18.9°C | 12.2°C | 5.5°C | 30.7°C | 0.3°C | 14 mm | 73% | 2.7 m/s | 4.5 |
| 1986 | 16.5°C | 10.9°C | 5.2°C | 21.6°C | 1.6°C | 51 mm | 81% | 3 m/s | 4.3 |
| 1985 | 17.1°C | 10.7°C | 4.3°C | 23.6°C | 1.2°C | 32 mm | 74% | 2.7 m/s | 4.8 |
| 1984 | 15.3°C | 9.8°C | 4.3°C | 22.2°C | 0.1°C | 47 mm | 77% | 3.1 m/s | 4.5 |
| 1983 | 16.2°C | 10.7°C | 5.2°C | 23.7°C | 1.0°C | 76 mm | 81% | 3.1 m/s | — |
| 1982 | 19.1°C | 11.9°C | 4.6°C | 28.2°C | -0.1°C | 14 mm | 61% | 3.1 m/s | — |
| 1981 | 17.9°C | 12.0°C | 6.2°C | 26.7°C | 3.0°C | 26 mm | 80% | 2.8 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 17.6°C with lows near 5.5°C (mean 11.6°C), based on 45 years of NASA POWER data.
September averages 45 mm of rainfall in Horsham, about average for rainfall. The wettest on record was 117 mm in 2016.
The hottest September reached 30.7°C in 1987. The coldest dipped to -0.4°C in 1995.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.1°C. Daytime highs moved from 17.1°C to 18.3°C and overnight lows from 4.9°C to 6°C over the same span.
September is one of the cooler months of the year in Horsham and about average for rainfall, so plan for around 17.6°C daytime highs and 5.5°C at night.
Not quite — September is the 4th coolest month in Horsham, averaging 11.6°C.
For September in Horsham, pack warm layers and a jacket for chilly mornings, with typical highs of 17.6°C and lows of 5.5°C.
Relative humidity in September averages 75% — moderately humid.
Average wind speed in September is 2.9 m/s. The windiest September on record averaged 3.7 m/s (1996).
The wettest September on record was 2016 with 117 mm. On average, September sees 45 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 Horsham 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.
