September is one of the warmer months of the year in Saint Helens, with average highs near 16.5°C and lows around 9.4°C (mean 13°C). It is about average for rainfall, averaging 82 mm of rainfall and 87% relative humidity across the period.
September is one of the warmer months of the year in Saint Helens. Across 45 years of records, the warmest September in Saint Helens was 2023 — when the month averaged 15.5°C — while the coldest was 1986 at 10.5°C. Typical September days reach 16.5°C with nights near 9.4°C. The long-term trend is warming, about 0.3°C per decade.
September is about average for rainfall in Saint Helens, averaging 82 mm of rainfall. The wettest September on record was 2000 with 147 mm, while the driest was 1986 at 16 mm.
Relative humidity in Saint Helens during September averages 87%. The most humid September was 2000 at 89%, and the least humid was 1991 at 82%.
September receives about 2.9 kWh/m²/day of solar energy in Saint Helens. The sunniest Septembers were 1986 and 1991 at 3.4 kWh/m²/day, and the cloudiest were 1993 and 2000 at 2.5.
Average wind speed in Saint Helens during September is 3.2 m/s. The windiest September was 1983 at 4.1 m/s, while the calmest was 2014 at 2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 12.4°C | 12.6°C | 13.3°C | 12.9°C | 13.8°C | +1.4°C |
| Avg High | 15.9°C | 16.2°C | 16.9°C | 16.5°C | 17.6°C | +1.7°C |
| Avg Low | 9.0°C | 8.9°C | 9.7°C | 9.3°C | 10.0°C | +1°C |
| Avg Rain | 78 mm | 76 mm | 82 mm | 84 mm | 95 mm | +17 mm |
September temperatures in Saint Helens have risen by about 1.2°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 2.6°C (1986) to a record high of 25°C (2021).
Rainfall in September is about average for rainfall, averaging 82 mm, with a wettest year of 147 mm.
One of the best times to visit Saint Helens
September is one of the best times to visit Saint Helens. Expect days averaging 16.5°C and nights around 9.4°C (mean 13°C) — warmer than Saint Helens's yearly average — with higher rainfall (82 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 | 16.8°C | 13.0°C | 9.3°C | 20.9°C | 3.7°C | 140 mm | 86% | 3.4 m/s | 2.8 |
| 2024 | 16.5°C | 13.0°C | 9.6°C | 23.1°C | 5.1°C | 117 mm | 88% | 3.3 m/s | 2.7 |
| 2023 🔥 | 19.3°C | 15.5°C | 11.6°C | 24.9°C | 7.0°C | 101 mm | 87% | 3 m/s | 2.8 |
| 2022 | 17.2°C | 13.5°C | 9.8°C | 21.4°C | 4.6°C | 93 mm | 86% | 2.9 m/s | 3 |
| 2021 | 18.9°C | 15.0°C | 11.1°C | 25.0°C | 8.1°C | 62 mm | 87% | 2.6 m/s | 2.8 |
| 2020 | 16.9°C | 12.9°C | 8.9°C | 23.9°C | 4.0°C | 53 mm | 86% | 3.1 m/s | 3.1 |
| 2019 | 16.6°C | 13.1°C | 9.6°C | 20.1°C | 5.5°C | 127 mm | 87% | 3.2 m/s | 2.9 |
| 2018 | 16.2°C | 12.6°C | 9.0°C | 21.5°C | 3.5°C | 79 mm | 85% | 3.4 m/s | 2.8 |
| 2017 | 15.8°C | 12.5°C | 9.2°C | 20.9°C | 5.7°C | 112 mm | 89% | 3.4 m/s | 2.7 |
| 2016 | 18.3°C | 14.7°C | 11.1°C | 23.8°C | 7.9°C | 65 mm | 88% | 3.2 m/s | 2.9 |
| 2015 | 15.7°C | 11.7°C | 7.8°C | 18.9°C | 5.6°C | 49 mm | 86% | 2.6 m/s | 3.3 |
| 2014 | 18.2°C | 13.8°C | 9.3°C | 20.5°C | 5.6°C | 18 mm | 86% | 2 m/s | 3.1 |
| 2013 | 16.2°C | 12.6°C | 9.0°C | 21.2°C | 5.9°C | 57 mm | 87% | 3.1 m/s | 2.6 |
| 2012 | 15.0°C | 11.7°C | 8.3°C | 20.6°C | 3.1°C | 141 mm | 88% | 3.6 m/s | 2.8 |
| 2011 | 17.1°C | 13.8°C | 10.5°C | 23.2°C | 8.0°C | 83 mm | 86% | 3.9 m/s | 2.8 |
| 2010 | 16.3°C | 12.8°C | 9.3°C | 20.4°C | 3.2°C | 105 mm | 87% | 3.5 m/s | 2.8 |
| 2009 | 16.4°C | 13.0°C | 9.6°C | 21.8°C | 6.6°C | 43 mm | 88% | 3.3 m/s | 2.8 |
| 2008 | 16.1°C | 12.7°C | 9.3°C | 19.1°C | 6.2°C | 109 mm | 89% | 2.9 m/s | 2.6 |
| 2007 | 16.1°C | 12.7°C | 9.3°C | 20.4°C | 3.9°C | 64 mm | 88% | 3.4 m/s | 2.9 |
| 2006 | 19.1°C | 15.3°C | 11.4°C | 23.9°C | 6.9°C | 77 mm | 87% | 3.2 m/s | 3.1 |
| 2005 | 17.5°C | 13.9°C | 10.3°C | 23.4°C | 6.0°C | 83 mm | 86% | 3.2 m/s | 2.9 |
| 2004 | 16.8°C | 13.5°C | 10.2°C | 23.1°C | 5.6°C | 83 mm | 87% | 4 m/s | 3.1 |
| 2003 | 17.2°C | 13.1°C | 9.0°C | 21.4°C | 5.5°C | 74 mm | 86% | 2.3 m/s | 3 |
| 2002 | 17.0°C | 13.2°C | 9.4°C | 20.5°C | 6.0°C | 48 mm | 86% | 2.2 m/s | 3.1 |
| 2001 | 15.5°C | 12.2°C | 8.9°C | 19.3°C | 6.0°C | 92 mm | 88% | 3.7 m/s | 2.6 |
| 2000 🌧️ | 16.9°C | 13.4°C | 10.0°C | 23.5°C | 4.5°C | 147 mm | 89% | 3.1 m/s | 2.5 |
| 1999 | 18.0°C | 14.3°C | 10.5°C | 23.4°C | 7.1°C | 106 mm | 87% | 3 m/s | 3 |
| 1998 | 16.9°C | 13.5°C | 10.0°C | 22.3°C | 5.3°C | 75 mm | 89% | 3.3 m/s | 3 |
| 1997 | 16.2°C | 12.7°C | 9.3°C | 19.0°C | 6.5°C | 44 mm | 87% | 3.4 m/s | 2.9 |
| 1996 | 16.4°C | 12.5°C | 8.6°C | 20.8°C | 5.5°C | 32 mm | 85% | 3.2 m/s | 3 |
| 1995 | 15.8°C | 12.4°C | 9.0°C | 18.8°C | 4.9°C | 104 mm | 86% | 3 m/s | 3 |
| 1994 | 14.4°C | 11.2°C | 8.0°C | 17.7°C | 5.2°C | 116 mm | 88% | 3.4 m/s | 2.8 |
| 1993 | 15.1°C | 11.3°C | 7.5°C | 20.2°C | 3.1°C | 79 mm | 86% | 3.4 m/s | 2.5 |
| 1992 | 15.7°C | 12.3°C | 8.8°C | 21.5°C | 6.1°C | 86 mm | 87% | 3.7 m/s | 3 |
| 1991 | 17.8°C | 13.4°C | 9.0°C | 24.2°C | 4.4°C | 49 mm | 82% | 3.1 m/s | 3.4 |
| 1990 | 15.2°C | 11.9°C | 8.6°C | 20.3°C | 5.4°C | 67 mm | 83% | 3.4 m/s | 2.8 |
| 1989 | 16.9°C | 13.2°C | 9.6°C | 21.2°C | 6.9°C | 31 mm | 85% | 3 m/s | 2.8 |
| 1988 | 15.0°C | 12.0°C | 8.9°C | 23.1°C | 3.7°C | 72 mm | 87% | 3.8 m/s | 2.6 |
| 1987 | 15.5°C | 12.1°C | 8.8°C | 19.8°C | 4.2°C | 88 mm | 87% | 3.2 m/s | 3.1 |
| 1986 ❄️ | 14.5°C | 10.5°C | 6.6°C | 18.9°C | 2.6°C | 16 mm | 85% | 2.6 m/s | 3.4 |
| 1985 | 16.6°C | 13.2°C | 9.8°C | 21.0°C | 6.9°C | 65 mm | 89% | 3.3 m/s | 2.7 |
| 1984 | 15.5°C | 12.4°C | 9.4°C | 22.1°C | 4.3°C | 130 mm | 85% | 3.5 m/s | 2.7 |
| 1983 | 15.5°C | 12.3°C | 9.1°C | 19.6°C | 5.5°C | 98 mm | 86% | 4.1 m/s | — |
| 1982 | 16.9°C | 13.0°C | 9.1°C | 23.0°C | 4.6°C | 85 mm | 87% | 3.2 m/s | — |
| 1981 | 16.7°C | 13.2°C | 9.7°C | 21.1°C | 6.5°C | 113 mm | 86% | 3.4 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 16.5°C with lows near 9.4°C (mean 13°C), based on 45 years of NASA POWER data.
September averages 82 mm of rainfall in Saint Helens, about average for rainfall. The wettest on record was 147 mm in 2000.
The hottest September reached 25°C in 2021. The coldest dipped to 2.6°C in 1986.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.2°C. Daytime highs moved from 16.2°C to 17.7°C and overnight lows from 9.4°C to 10.3°C over the same span.
September is one of the warmer months of the year in Saint Helens and about average for rainfall, so plan for around 16.5°C daytime highs and 9.4°C at night.
Not quite — September is the 9th coolest month in Saint Helens, averaging 13°C.
For September in Saint Helens, pack light layers you can adjust through the day, with typical highs of 16.5°C and lows of 9.4°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 87% — quite humid.
Average wind speed in September is 3.2 m/s. The windiest September on record averaged 4.1 m/s (1983).
The wettest September on record was 2000 with 147 mm. On average, September sees 82 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 Saint Helens 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.
