September is one of the warmer months of the year in Duluth, with average highs near 29.1°C and lows around 16.7°C (mean 22.9°C). It is one of the drier months, averaging 97 mm of rainfall and 70% relative humidity across the period.
September is one of the warmer months of the year in Duluth. Across 45 years of records, the warmest September in Duluth was 2019 — when the month averaged 27.7°C — while the coldest was 1994 at 20.3°C. Typical September days reach 29.1°C with nights near 16.7°C. The long-term trend is warming, about 0.5°C per decade.
September is one of the drier months in Duluth, averaging 97 mm of rainfall. The wettest September on record was 2009 with 274 mm, while the driest was 1984 at 10 mm.
Relative humidity in Duluth during September averages 70%. The most humid September was 1992 at 84%, and the least humid was 1999 at 52%.
September receives about 4.7 kWh/m²/day of solar energy in Duluth. The sunniest September was 2019 at 5.8 kWh/m²/day, and the cloudiest was 2009 at 3.8.
Average wind speed in Duluth during September is 1 m/s. The windiest September was 2004 at 1.5 m/s, while the calmest were 2014, 2023 and 2025 at 0.8 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 22.0°C | 22.7°C | 22.6°C | 24.1°C | 23.1°C | +1.1°C |
| Avg High | 28.1°C | 29.0°C | 28.7°C | 30.5°C | 29.2°C | +1.1°C |
| Avg Low | 15.9°C | 16.3°C | 16.6°C | 17.8°C | 17.1°C | +1.2°C |
| Avg Rain | 95 mm | 98 mm | 114 mm | 74 mm | 107 mm | +12 mm |
September temperatures in Duluth have risen by about 1.7°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 4.6°C (1983) to a record high of 38.9°C (2019).
Rainfall in September is one of the drier months, averaging 97 mm, with a wettest year of 274 mm.
One of the best times to visit Duluth
September is one of the best times to visit Duluth. Expect days averaging 29.1°C and nights around 16.7°C (mean 22.9°C) — warmer than Duluth's yearly average — with higher rainfall (97 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 | 31.1°C | 24.4°C | 17.7°C | 34.1°C | 13.3°C | 52 mm | 65% | 0.8 m/s | 5 |
| 2024 | 30.1°C | 24.3°C | 18.5°C | 36.8°C | 15.0°C | 229 mm | 68% | 1.2 m/s | 4.2 |
| 2023 | 29.8°C | 23.4°C | 17.1°C | 33.7°C | 12.4°C | 47 mm | 66% | 0.8 m/s | 5.1 |
| 2022 | 29.1°C | 22.4°C | 15.8°C | 35.4°C | 7.4°C | 68 mm | 68% | 1 m/s | 5.2 |
| 2021 | 27.9°C | 22.2°C | 16.5°C | 33.5°C | 8.5°C | 92 mm | 75% | 0.9 m/s | 4.9 |
| 2020 | 27.3°C | 22.0°C | 16.8°C | 33.8°C | 8.1°C | 157 mm | 77% | 1.1 m/s | 4.7 |
| 2019 🔥 | 35.3°C | 27.7°C | 20.1°C | 38.9°C | 14.4°C | 17 mm | 54% | 0.9 m/s | 5.8 |
| 2018 | 32.1°C | 26.3°C | 20.4°C | 35.8°C | 18.2°C | 71 mm | 71% | 0.9 m/s | 4.5 |
| 2017 | 28.5°C | 22.2°C | 15.8°C | 33.5°C | 9.9°C | 116 mm | 69% | 1 m/s | 5.2 |
| 2016 | 32.6°C | 25.8°C | 18.9°C | 36.3°C | 9.8°C | 53 mm | 62% | 0.9 m/s | 5.5 |
| 2015 | 28.6°C | 22.9°C | 17.2°C | 34.7°C | 9.8°C | 103 mm | 73% | 0.9 m/s | 4.7 |
| 2014 | 30.2°C | 24.2°C | 18.3°C | 34.4°C | 11.8°C | 65 mm | 72% | 0.8 m/s | 4.7 |
| 2013 | 27.4°C | 21.9°C | 16.3°C | 30.6°C | 10.7°C | 69 mm | 80% | 0.9 m/s | 5 |
| 2012 | 29.4°C | 22.9°C | 16.4°C | 35.4°C | 7.5°C | 73 mm | 69% | 0.9 m/s | 4.5 |
| 2011 | 28.7°C | 22.6°C | 16.4°C | 37.0°C | 11.5°C | 97 mm | 69% | 1.1 m/s | 4.4 |
| 2010 | 32.2°C | 24.9°C | 17.7°C | 36.1°C | 12.1°C | 78 mm | 60% | 0.9 m/s | 5.4 |
| 2009 🌧️ | 27.0°C | 22.3°C | 17.7°C | 30.7°C | 7.5°C | 274 mm | 80% | 0.9 m/s | 3.8 |
| 2008 | 29.7°C | 23.3°C | 16.9°C | 34.3°C | 9.7°C | 17 mm | 69% | 1.1 m/s | 4.9 |
| 2007 | 31.5°C | 24.7°C | 17.8°C | 35.5°C | 10.1°C | 43 mm | 62% | 1 m/s | 5.2 |
| 2006 | 28.6°C | 22.1°C | 15.6°C | 33.2°C | 8.4°C | 86 mm | 70% | 1 m/s | 4.6 |
| 2005 | 30.8°C | 24.0°C | 17.2°C | 34.6°C | 14.4°C | 13 mm | 67% | 1 m/s | 5.4 |
| 2004 | 26.4°C | 21.3°C | 16.3°C | 31.3°C | 9.3°C | 268 mm | 81% | 1.5 m/s | 4.4 |
| 2003 | 27.1°C | 21.2°C | 15.3°C | 31.1°C | 5.9°C | 70 mm | 76% | 1 m/s | 5.1 |
| 2002 | 30.1°C | 24.5°C | 19.0°C | 37.3°C | 14.9°C | 175 mm | 72% | 1.2 m/s | 4.2 |
| 2001 | 28.5°C | 21.6°C | 14.7°C | 33.1°C | 5.3°C | 65 mm | 66% | 1 m/s | 5 |
| 2000 | 27.1°C | 21.3°C | 15.4°C | 31.9°C | 6.2°C | 126 mm | 76% | 1.1 m/s | 4.3 |
| 1999 | 30.9°C | 22.9°C | 15.0°C | 37.0°C | 7.1°C | 57 mm | 52% | 1.1 m/s | 5.3 |
| 1998 | 31.7°C | 24.7°C | 17.8°C | 35.7°C | 11.5°C | 57 mm | 65% | 1 m/s | 5 |
| 1997 | 30.2°C | 23.7°C | 17.2°C | 35.4°C | 10.8°C | 165 mm | 64% | 0.9 m/s | 4.7 |
| 1996 | 27.7°C | 21.7°C | 15.6°C | 32.7°C | 9.2°C | 125 mm | 72% | 1.1 m/s | 4.5 |
| 1995 | 28.1°C | 22.1°C | 16.1°C | 33.3°C | 9.8°C | 84 mm | 75% | 1 m/s | 4.3 |
| 1994 ❄️ | 25.9°C | 20.3°C | 14.8°C | 29.9°C | 8.5°C | 116 mm | 80% | 0.9 m/s | 4.8 |
| 1993 | 31.0°C | 23.9°C | 16.8°C | 35.7°C | 5.5°C | 61 mm | 63% | 1 m/s | 4.7 |
| 1992 | 26.4°C | 21.6°C | 16.9°C | 29.7°C | 7.9°C | 134 mm | 84% | 0.9 m/s | 4 |
| 1991 | 27.7°C | 21.9°C | 16.1°C | 34.4°C | 6.5°C | 79 mm | 76% | 0.9 m/s | 4.8 |
| 1990 | 30.3°C | 23.7°C | 17.0°C | 36.9°C | 6.2°C | 101 mm | 65% | 0.9 m/s | 5.1 |
| 1989 | 26.5°C | 21.5°C | 16.5°C | 31.9°C | 9.5°C | 235 mm | 80% | 1.1 m/s | 3.9 |
| 1988 | 27.3°C | 22.0°C | 16.7°C | 31.8°C | 11.7°C | 153 mm | 80% | 1.1 m/s | 4 |
| 1987 | 29.5°C | 23.1°C | 16.8°C | 33.6°C | 10.6°C | 73 mm | 66% | 0.9 m/s | 4.4 |
| 1986 | 29.1°C | 23.5°C | 18.0°C | 34.2°C | 13.5°C | 81 mm | 76% | 0.9 m/s | 4.2 |
| 1985 | 28.5°C | 21.8°C | 15.1°C | 32.8°C | 7.3°C | 49 mm | 67% | 1 m/s | 5 |
| 1984 | 28.0°C | 21.1°C | 14.2°C | 33.7°C | 8.9°C | 10 mm | 66% | 1 m/s | 5 |
| 1983 | 26.8°C | 21.1°C | 15.5°C | 33.7°C | 4.6°C | 142 mm | 74% | 1 m/s | — |
| 1982 | 28.1°C | 21.7°C | 15.3°C | 33.4°C | 6.4°C | 51 mm | 68% | 0.9 m/s | — |
| 1981 | 29.5°C | 22.4°C | 15.3°C | 32.5°C | 7.4°C | 61 mm | 61% | 0.9 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 29.1°C with lows near 16.7°C (mean 22.9°C), based on 45 years of NASA POWER data.
September averages 97 mm of rainfall in Duluth, one of the drier months. The wettest on record was 274 mm in 2009.
The hottest September reached 38.9°C in 2019. The coldest dipped to 4.6°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.7°C. Daytime highs moved from 28.2°C to 29.6°C and overnight lows from 15.1°C to 17.1°C over the same span.
September is one of the warmer months of the year in Duluth and one of the drier months, so plan for around 29.1°C daytime highs and 16.7°C at night.
Not quite — September is the 9th coolest month in Duluth, averaging 22.9°C.
For September in Duluth, pack light layers you can adjust through the day, with typical highs of 29.1°C and lows of 16.7°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 70% — moderately humid.
Average wind speed in September is 1 m/s. The windiest September on record averaged 1.5 m/s (2004).
The wettest September on record was 2009 with 274 mm. On average, September sees 97 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 Duluth 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.
