September is one of the warmer months of the year in Portland, with average highs near 17.9°C and lows around 13.9°C (mean 15.9°C). It is one of the drier months, averaging 94 mm of rainfall and 83% relative humidity across the period.
September is one of the warmer months of the year in Portland. Across 45 years of records, the warmest September in Portland was 2015 — when the month averaged 17.7°C — while the coldest was 1986 at 13.9°C. Typical September days reach 17.9°C with nights near 13.9°C. The long-term trend is warming, about 0.6°C per decade.
September is one of the drier months in Portland, averaging 94 mm of rainfall. The wettest September on record was 2008 with 268 mm, while the driest was 2020 at 28 mm.
Relative humidity in Portland during September averages 83%. The most humid September was 2011 at 88%, and the least humid was 1995 at 75%.
September receives about 4.2 kWh/m²/day of solar energy in Portland. The sunniest September was 1984 at 4.8 kWh/m²/day, and the cloudiest was 1996 at 3.5.
Average wind speed in Portland during September is 3 m/s. The windiest Septembers were 1988, 1991 and 2020, among others at 3.4 m/s, while the calmest was 2003 at 2.6 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 15.0°C | 15.1°C | 15.9°C | 16.7°C | 17.0°C | +2°C |
| Avg High | 17.2°C | 17.1°C | 17.8°C | 18.6°C | 18.9°C | +1.7°C |
| Avg Low | 12.8°C | 13.2°C | 13.9°C | 14.7°C | 15.1°C | +2.3°C |
| Avg Rain | 76 mm | 111 mm | 102 mm | 96 mm | 81 mm | +4 mm |
September temperatures in Portland have risen by about 1.8°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 4.8°C (1992) to a record high of 25.6°C (1989).
Rainfall in September is one of the drier months, averaging 94 mm, with a wettest year of 268 mm.
One of the best times to visit Portland
September is one of the best times to visit Portland. Expect days averaging 17.9°C and nights around 13.9°C (mean 15.9°C) — warmer than Portland's yearly average — with higher rainfall (94 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 | 19.2°C | 17.1°C | 15.1°C | 22.1°C | 11.8°C | 55 mm | 83% | 2.7 m/s | 4.5 |
| 2024 | 18.6°C | 16.7°C | 14.8°C | 21.7°C | 12.8°C | 31 mm | 84% | 2.9 m/s | 4.4 |
| 2023 | 19.2°C | 17.5°C | 15.9°C | 24.9°C | 11.5°C | 105 mm | 87% | 2.7 m/s | 4 |
| 2022 | 18.6°C | 16.5°C | 14.5°C | 22.7°C | 9.9°C | 89 mm | 82% | 3.2 m/s | 4.1 |
| 2021 | 19.3°C | 17.6°C | 15.9°C | 21.1°C | 12.0°C | 175 mm | 85% | 3.2 m/s | 4 |
| 2020 | 18.5°C | 16.6°C | 14.6°C | 22.2°C | 9.4°C | 28 mm | 79% | 3.4 m/s | 4.3 |
| 2019 | 18.2°C | 16.2°C | 14.2°C | 21.8°C | 10.1°C | 53 mm | 81% | 3.1 m/s | 4.4 |
| 2018 | 19.0°C | 17.2°C | 15.5°C | 25.3°C | 10.3°C | 144 mm | 83% | 2.9 m/s | 3.9 |
| 2017 | 19.0°C | 16.9°C | 14.8°C | 21.2°C | 11.6°C | 67 mm | 84% | 2.8 m/s | 4.2 |
| 2016 | 19.2°C | 17.2°C | 15.2°C | 24.0°C | 10.4°C | 39 mm | 81% | 3 m/s | 4.2 |
| 2015 🔥 | 19.9°C | 17.7°C | 15.5°C | 24.7°C | 10.8°C | 160 mm | 83% | 2.8 m/s | 4.7 |
| 2014 | 18.2°C | 16.2°C | 14.1°C | 23.4°C | 8.7°C | 29 mm | 82% | 2.8 m/s | 4.6 |
| 2013 | 17.5°C | 15.4°C | 13.3°C | 22.9°C | 9.0°C | 166 mm | 83% | 3 m/s | 4.3 |
| 2012 | 18.1°C | 16.3°C | 14.4°C | 21.3°C | 11.6°C | 109 mm | 83% | 3.2 m/s | 4 |
| 2011 | 18.4°C | 16.8°C | 15.2°C | 20.8°C | 10.8°C | 104 mm | 88% | 2.8 m/s | 4 |
| 2010 | 18.7°C | 16.9°C | 15.1°C | 25.3°C | 11.4°C | 85 mm | 83% | 3.3 m/s | 4 |
| 2009 | 17.1°C | 15.2°C | 13.3°C | 20.4°C | 8.6°C | 41 mm | 84% | 3.1 m/s | 4.7 |
| 2008 🌧️ | 17.2°C | 15.5°C | 13.9°C | 21.3°C | 9.7°C | 268 mm | 87% | 2.8 m/s | 4.1 |
| 2007 | 18.1°C | 16.0°C | 13.9°C | 22.4°C | 10.7°C | 73 mm | 82% | 2.7 m/s | 4.5 |
| 2006 | 17.3°C | 15.5°C | 13.8°C | 20.1°C | 9.5°C | 91 mm | 86% | 2.9 m/s | 4.1 |
| 2005 | 18.7°C | 16.7°C | 14.6°C | 22.6°C | 10.5°C | 71 mm | 84% | 2.9 m/s | 4.4 |
| 2004 | 17.5°C | 15.6°C | 13.7°C | 20.3°C | 10.4°C | 90 mm | 84% | 2.9 m/s | 4.4 |
| 2003 | 18.0°C | 16.3°C | 14.5°C | 20.3°C | 12.1°C | 124 mm | 86% | 2.6 m/s | 4.1 |
| 2002 | 18.7°C | 16.6°C | 14.6°C | 25.6°C | 10.2°C | 110 mm | 82% | 3 m/s | 4.2 |
| 2001 | 18.2°C | 16.1°C | 14.0°C | 22.2°C | 9.7°C | 82 mm | 80% | 3.2 m/s | 4.5 |
| 2000 | 17.3°C | 15.2°C | 13.0°C | 23.1°C | 6.7°C | 66 mm | 80% | 3.1 m/s | 4 |
| 1999 | 18.8°C | 17.1°C | 15.4°C | 23.2°C | 11.1°C | 216 mm | 88% | 3.2 m/s | 4 |
| 1998 | 18.0°C | 15.8°C | 13.6°C | 22.0°C | 9.3°C | 56 mm | 83% | 2.9 m/s | 4.5 |
| 1997 | 16.8°C | 14.9°C | 13.0°C | 19.9°C | 8.0°C | 74 mm | 83% | 3 m/s | 4 |
| 1996 | 16.5°C | 14.8°C | 13.2°C | 22.2°C | 8.8°C | 131 mm | 87% | 3.2 m/s | 3.5 |
| 1995 | 16.8°C | 14.7°C | 12.6°C | 22.4°C | 8.8°C | 60 mm | 75% | 3.3 m/s | 4.3 |
| 1994 | 16.6°C | 14.7°C | 12.8°C | 20.8°C | 10.2°C | 169 mm | 83% | 3.3 m/s | 3.9 |
| 1993 | 17.1°C | 15.1°C | 13.1°C | 21.3°C | 7.9°C | 104 mm | 81% | 3.3 m/s | 3.7 |
| 1992 | 16.6°C | 14.5°C | 12.5°C | 20.3°C | 4.8°C | 76 mm | 83% | 3.1 m/s | 4.3 |
| 1991 | 16.7°C | 14.5°C | 12.3°C | 20.6°C | 6.1°C | 153 mm | 81% | 3.4 m/s | 4.2 |
| 1990 | 17.1°C | 15.2°C | 13.4°C | 21.7°C | 8.5°C | 69 mm | 82% | 3.2 m/s | 3.8 |
| 1989 | 17.4°C | 15.2°C | 13.0°C | 25.6°C | 7.1°C | 102 mm | 82% | 3.1 m/s | 4.2 |
| 1988 | 16.8°C | 14.5°C | 12.3°C | 20.0°C | 8.6°C | 51 mm | 81% | 3.4 m/s | 4.5 |
| 1987 | 16.9°C | 14.9°C | 13.0°C | 20.9°C | 8.7°C | 151 mm | 83% | 3.4 m/s | 4 |
| 1986 ❄️ | 16.0°C | 13.9°C | 11.7°C | 20.8°C | 6.1°C | 70 mm | 82% | 3.1 m/s | 3.9 |
| 1985 | 17.4°C | 15.1°C | 12.9°C | 21.8°C | 10.1°C | 86 mm | 82% | 2.9 m/s | 4.1 |
| 1984 | 16.8°C | 14.5°C | 12.3°C | 21.8°C | 7.6°C | 29 mm | 77% | 3.1 m/s | 4.8 |
| 1983 | 19.3°C | 16.7°C | 14.1°C | 23.9°C | 9.6°C | 30 mm | 78% | 2.7 m/s | — |
| 1982 | 17.1°C | 15.1°C | 13.2°C | 22.3°C | 11.4°C | 51 mm | 84% | 2.8 m/s | — |
| 1981 | 17.5°C | 15.3°C | 13.1°C | 21.0°C | 7.2°C | 117 mm | 81% | 3.2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 17.9°C with lows near 13.9°C (mean 15.9°C), based on 45 years of NASA POWER data.
September averages 94 mm of rainfall in Portland, one of the drier months. The wettest on record was 268 mm in 2008.
The hottest September reached 25.6°C in 1989. The coldest dipped to 4.8°C in 1992.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.8°C. Daytime highs moved from 17.6°C to 19°C and overnight lows from 13.1°C to 15.2°C over the same span.
September is one of the warmer months of the year in Portland and one of the drier months, so plan for around 17.9°C daytime highs and 13.9°C at night.
Not quite — September is the 10th coolest month in Portland, averaging 15.9°C.
For September in Portland, pack light layers you can adjust through the day, with typical highs of 17.9°C and lows of 13.9°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 83% — quite humid.
Average wind speed in September is 3 m/s. The windiest September on record averaged 3.4 m/s (1987).
The wettest September on record was 2008 with 268 mm. On average, September sees 94 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.
