September is one of the cooler months of the year in Portland, with average highs near 14.2°C and lows around 10.5°C (mean 12.4°C). It is a relatively wet time of year, averaging 77 mm of rainfall and 78% relative humidity across the period.
September is one of the cooler months of the year in Portland. Across 45 years of records, the warmest Septembers in Portland were 2013 and 2023 — when the month averaged 13.6°C — while the coldest was 1992 at 10.7°C. Typical September days reach 14.2°C with nights near 10.5°C. The long-term trend is warming, about 0.2°C per decade.
September is a relatively wet time of year in Portland, averaging 77 mm of rainfall. The wettest September on record was 1996 with 139 mm, while the driest was 2023 at 22 mm.
Relative humidity in Portland during September averages 78%. The most humid September was 2013 at 81%, and the least humid was 1982 at 74%.
September receives about 4 kWh/m²/day of solar energy in Portland. The sunniest September was 1985 at 4.6 kWh/m²/day, and the cloudiest were 2000 and 2016 at 3.5.
Average wind speed in Portland during September is 5.9 m/s. The windiest September was 2003 at 7.4 m/s, while the calmest was 1997 at 4.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 12.2°C | 12.0°C | 12.5°C | 12.4°C | 12.8°C | +0.6°C |
| Avg High | 14.0°C | 13.8°C | 14.4°C | 14.2°C | 14.6°C | +0.6°C |
| Avg Low | 10.3°C | 10.3°C | 10.6°C | 10.6°C | 11.0°C | +0.7°C |
| Avg Rain | 77 mm | 90 mm | 83 mm | 67 mm | 61 mm | -16 mm |
September temperatures in Portland have risen by about 0.8°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 7.2°C (2004) to a record high of 22.8°C (2023).
Rainfall in September is a relatively wet time of year, averaging 77 mm, with a wettest year of 139 mm.
A quieter season to visit Portland
If your dates are flexible, the more temperate months of February and January tend to be the most comfortable for visiting Portland. That said, September — with days averaging 14.2°C and nights around 10.5°C (mean 12.4°C) and moderate rainfall (77 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 | 14.5°C | 12.8°C | 11.1°C | 19.7°C | 8.9°C | 70 mm | 76% | 6.8 m/s | 4.1 |
| 2024 | 14.5°C | 13.0°C | 11.5°C | 18.7°C | 9.6°C | 63 mm | 76% | 6.9 m/s | 3.6 |
| 2023 | 15.8°C | 13.6°C | 11.5°C | 22.8°C | 9.5°C | 22 mm | 75% | 5.4 m/s | 4.5 |
| 2022 | 13.7°C | 12.2°C | 10.7°C | 16.9°C | 8.8°C | 73 mm | 80% | 5.4 m/s | 3.8 |
| 2021 | 14.3°C | 12.5°C | 10.8°C | 20.9°C | 9.2°C | 51 mm | 77% | 6.4 m/s | 4 |
| 2020 | 14.6°C | 12.5°C | 10.4°C | 19.6°C | 8.0°C | 84 mm | 78% | 6.1 m/s | 4.1 |
| 2019 | 13.8°C | 11.9°C | 10.0°C | 18.9°C | 8.3°C | 52 mm | 77% | 5.3 m/s | 4.1 |
| 2018 | 14.0°C | 12.1°C | 10.2°C | 20.0°C | 8.7°C | 25 mm | 75% | 5.9 m/s | 4.1 |
| 2017 | 14.1°C | 12.3°C | 10.6°C | 19.0°C | 8.6°C | 66 mm | 75% | 6.9 m/s | 3.9 |
| 2016 | 13.7°C | 12.0°C | 10.3°C | 17.4°C | 9.1°C | 130 mm | 81% | 5 m/s | 3.5 |
| 2015 | 13.9°C | 12.2°C | 10.4°C | 20.3°C | 8.1°C | 31 mm | 78% | 4.7 m/s | 4.2 |
| 2014 | 14.8°C | 13.0°C | 11.2°C | 21.8°C | 9.6°C | 38 mm | 76% | 5.2 m/s | 4.4 |
| 2013 🔥 | 15.5°C | 13.6°C | 11.8°C | 19.6°C | 9.1°C | 90 mm | 81% | 6 m/s | 3.7 |
| 2012 | 14.3°C | 12.4°C | 10.6°C | 18.4°C | 8.6°C | 74 mm | 77% | 5.8 m/s | 4.2 |
| 2011 | 14.7°C | 12.8°C | 10.9°C | 20.9°C | 9.0°C | 77 mm | 77% | 5.8 m/s | 4 |
| 2010 | 13.0°C | 11.7°C | 10.4°C | 15.7°C | 9.1°C | 81 mm | 79% | 5.9 m/s | 3.7 |
| 2009 | 14.6°C | 12.8°C | 10.9°C | 20.7°C | 9.5°C | 112 mm | 77% | 6.5 m/s | 3.8 |
| 2008 | 14.3°C | 12.2°C | 10.2°C | 18.1°C | 8.2°C | 66 mm | 76% | 6 m/s | 4.2 |
| 2007 | 14.8°C | 12.6°C | 10.5°C | 18.2°C | 7.7°C | 93 mm | 76% | 6.6 m/s | 4 |
| 2006 | 14.5°C | 12.5°C | 10.6°C | 18.4°C | 9.0°C | 67 mm | 74% | 5.8 m/s | 4 |
| 2005 | 14.5°C | 12.7°C | 11.0°C | 20.3°C | 9.5°C | 74 mm | 76% | 5.3 m/s | 4.1 |
| 2004 | 13.8°C | 12.1°C | 10.4°C | 19.6°C | 7.2°C | 76 mm | 80% | 5 m/s | 3.9 |
| 2003 | 13.6°C | 11.7°C | 9.8°C | 18.3°C | 7.5°C | 81 mm | 76% | 7.4 m/s | 4.1 |
| 2002 | 14.2°C | 12.3°C | 10.5°C | 21.4°C | 9.1°C | 77 mm | 75% | 7.1 m/s | 4 |
| 2001 | 15.6°C | 13.5°C | 11.5°C | 20.2°C | 9.4°C | 67 mm | 79% | 5.4 m/s | 3.8 |
| 2000 | 14.5°C | 12.7°C | 11.0°C | 18.3°C | 9.3°C | 122 mm | 80% | 7.3 m/s | 3.5 |
| 1999 | 15.4°C | 13.3°C | 11.3°C | 22.0°C | 9.5°C | 50 mm | 77% | 5.1 m/s | 3.8 |
| 1998 | 15.0°C | 13.0°C | 11.0°C | 18.8°C | 9.0°C | 89 mm | 78% | 5.9 m/s | 3.9 |
| 1997 | 13.8°C | 12.1°C | 10.4°C | 16.0°C | 8.2°C | 74 mm | 80% | 4.2 m/s | 4.2 |
| 1996 🌧️ | 13.4°C | 11.7°C | 9.9°C | 19.2°C | 7.6°C | 139 mm | 78% | 7.3 m/s | 4 |
| 1995 | 13.5°C | 11.7°C | 9.8°C | 17.7°C | 7.3°C | 57 mm | 79% | 5.5 m/s | 4 |
| 1994 | 12.7°C | 11.1°C | 9.6°C | 17.0°C | 8.0°C | 74 mm | 76% | 6.1 m/s | 4.1 |
| 1993 | 14.4°C | 12.4°C | 10.4°C | 20.7°C | 8.8°C | 103 mm | 79% | 5.1 m/s | 4.2 |
| 1992 ❄️ | 12.0°C | 10.7°C | 9.4°C | 14.2°C | 8.3°C | 118 mm | 80% | 5.2 m/s | 3.7 |
| 1991 | 13.8°C | 12.1°C | 10.5°C | 17.6°C | 8.2°C | 110 mm | 79% | 5.8 m/s | 3.8 |
| 1990 | 14.1°C | 12.3°C | 10.5°C | 18.2°C | 9.1°C | 88 mm | 78% | 5.6 m/s | 4.3 |
| 1989 | 14.0°C | 12.0°C | 10.1°C | 18.4°C | 7.9°C | 70 mm | 80% | 5.4 m/s | 4.2 |
| 1988 | 14.9°C | 12.9°C | 10.8°C | 18.8°C | 8.7°C | 87 mm | 79% | 5.6 m/s | 3.9 |
| 1987 | 14.6°C | 12.7°C | 10.8°C | 22.6°C | 8.2°C | 40 mm | 78% | 5.5 m/s | 4 |
| 1986 | 13.5°C | 11.9°C | 10.3°C | 18.8°C | 8.2°C | 92 mm | 80% | 5.8 m/s | 4.1 |
| 1985 | 13.4°C | 11.8°C | 10.1°C | 18.5°C | 8.2°C | 39 mm | 78% | 5.1 m/s | 4.6 |
| 1984 | 12.7°C | 11.1°C | 9.5°C | 17.3°C | 8.3°C | 132 mm | 78% | 5.9 m/s | 3.7 |
| 1983 | 13.8°C | 12.1°C | 10.4°C | 18.7°C | 8.5°C | 126 mm | 78% | 6.5 m/s | — |
| 1982 | 14.0°C | 11.9°C | 9.9°C | 20.1°C | 8.6°C | 54 mm | 74% | 5.9 m/s | — |
| 1981 | 15.0°C | 13.0°C | 11.0°C | 20.1°C | 9.5°C | 49 mm | 80% | 6 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 14.2°C with lows near 10.5°C (mean 12.4°C), based on 45 years of NASA POWER data.
September averages 77 mm of rainfall in Portland, a relatively wet time of year. The wettest on record was 139 mm in 1996.
The hottest September reached 22.8°C in 2023. The coldest dipped to 7.2°C in 2004.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 0.8°C. Daytime highs moved from 13.8°C to 14.6°C and overnight lows from 10.2°C to 11.1°C over the same span.
September is one of the cooler months of the year in Portland and a relatively wet time of year, so plan for around 14.2°C daytime highs and 10.5°C at night.
Not quite — September is the 3rd coolest month in Portland, averaging 12.4°C.
For September in Portland, pack light layers you can adjust through the day, with typical highs of 14.2°C and lows of 10.5°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 78% — quite humid.
Average wind speed in September is 5.9 m/s. The windiest September on record averaged 7.4 m/s (2003).
The wettest September on record was 1996 with 139 mm. On average, September sees 77 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 Portland 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.
