September is one of the warmer months of the year in Knoxville, with average highs near 28.1°C and lows around 15.2°C (mean 21.7°C). It is one of the drier months, averaging 89 mm of rainfall and 68% relative humidity across the period.
September is one of the warmer months of the year in Knoxville. Across 45 years of records, the warmest September in Knoxville was 2019 — when the month averaged 26°C — while the coldest was 2006 at 19.5°C. Typical September days reach 28.1°C with nights near 15.2°C. The long-term trend is warming, about 0.4°C per decade.
September is one of the drier months in Knoxville, averaging 89 mm of rainfall. The wettest September on record was 1989 with 229 mm, while the driest was 2019 at 8 mm.
Relative humidity in Knoxville during September averages 68%. The most humid September was 1989 at 83%, and the least humid was 1999 at 46%.
September receives about 4.6 kWh/m²/day of solar energy in Knoxville. The sunniest September was 2019 at 5.6 kWh/m²/day, and the cloudiest were 1988, 1992 and 2009 at 3.9.
Average wind speed in Knoxville during September is 0.7 m/s. The windiest Septembers were 2017, 2022 and 2024, among others at 0.8 m/s, while the calmest were 2015, 2019 and 2023, among others at 0.6 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 20.8°C | 21.7°C | 21.5°C | 22.5°C | 21.7°C | +0.9°C |
| Avg High | 27.2°C | 28.5°C | 28.1°C | 28.7°C | 27.9°C | +0.7°C |
| Avg Low | 14.3°C | 15.0°C | 15.0°C | 16.3°C | 15.6°C | +1.3°C |
| Avg Rain | 89 mm | 70 mm | 100 mm | 93 mm | 96 mm | +7 mm |
September temperatures in Knoxville have risen by about 1.5°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 3.4°C (1993) to a record high of 37.5°C (2011).
Rainfall in September is one of the drier months, averaging 89 mm, with a wettest year of 229 mm.
Daytime highs and overnight lows have shifted differently — highs rose about 0.3°C per decade while lows rose 0.5°C per decade, narrowing the gap between day and night.
One of the best times to visit Knoxville
September is one of the best times to visit Knoxville. Expect days averaging 28.1°C and nights around 15.2°C (mean 21.7°C) — warmer than Knoxville's yearly average — with higher rainfall (89 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 | 28.1°C | 22.1°C | 16.1°C | 31.5°C | 10.3°C | 109 mm | 69% | 0.7 m/s | 4.7 |
| 2024 | 28.9°C | 22.7°C | 16.5°C | 34.1°C | 8.9°C | 165 mm | 67% | 0.8 m/s | 4.2 |
| 2023 | 29.2°C | 22.8°C | 16.4°C | 32.4°C | 11.6°C | 35 mm | 68% | 0.6 m/s | 5.1 |
| 2022 | 27.7°C | 21.1°C | 14.4°C | 34.8°C | 5.3°C | 71 mm | 67% | 0.8 m/s | 5 |
| 2021 | 26.2°C | 20.6°C | 15.0°C | 30.3°C | 8.8°C | 81 mm | 76% | 0.7 m/s | 4.9 |
| 2020 | 27.1°C | 21.0°C | 15.0°C | 31.7°C | 6.7°C | 116 mm | 75% | 0.7 m/s | 4.5 |
| 2019 🔥 | 33.1°C | 26.0°C | 18.9°C | 37.0°C | 14.7°C | 8 mm | 58% | 0.6 m/s | 5.6 |
| 2018 | 30.0°C | 24.7°C | 19.5°C | 33.8°C | 14.1°C | 156 mm | 75% | 0.7 m/s | 4.3 |
| 2017 | 27.3°C | 21.0°C | 14.7°C | 32.2°C | 8.9°C | 61 mm | 68% | 0.8 m/s | 4.8 |
| 2016 | 31.3°C | 24.4°C | 17.5°C | 35.1°C | 8.6°C | 42 mm | 60% | 0.7 m/s | 5.3 |
| 2015 | 28.5°C | 22.3°C | 16.0°C | 33.6°C | 8.3°C | 85 mm | 68% | 0.6 m/s | 4.6 |
| 2014 | 28.2°C | 22.1°C | 16.1°C | 32.5°C | 7.4°C | 61 mm | 73% | 0.6 m/s | 4.6 |
| 2013 | 26.9°C | 20.8°C | 14.8°C | 31.7°C | 8.5°C | 95 mm | 74% | 0.6 m/s | 4.8 |
| 2012 | 26.6°C | 20.5°C | 14.3°C | 34.1°C | 4.1°C | 142 mm | 72% | 0.7 m/s | 4.6 |
| 2011 | 26.0°C | 20.4°C | 14.9°C | 37.5°C | 8.9°C | 162 mm | 73% | 0.7 m/s | 4.3 |
| 2010 | 29.1°C | 22.5°C | 15.8°C | 34.9°C | 10.3°C | 119 mm | 65% | 0.7 m/s | 5.1 |
| 2009 | 26.0°C | 21.1°C | 16.2°C | 30.3°C | 6.5°C | 162 mm | 78% | 0.6 m/s | 3.9 |
| 2008 | 29.1°C | 22.3°C | 15.5°C | 33.6°C | 9.0°C | 42 mm | 66% | 0.8 m/s | 4.9 |
| 2007 | 30.9°C | 23.6°C | 16.3°C | 35.4°C | 8.4°C | 45 mm | 58% | 0.7 m/s | 5.2 |
| 2006 ❄️ | 25.5°C | 19.5°C | 13.5°C | 30.6°C | 6.4°C | 135 mm | 74% | 0.7 m/s | 4.2 |
| 2005 | 31.4°C | 23.6°C | 15.9°C | 34.1°C | 8.8°C | 34 mm | 59% | 0.8 m/s | 5.4 |
| 2004 | 26.7°C | 20.7°C | 14.7°C | 32.7°C | 7.6°C | 167 mm | 77% | 0.8 m/s | 4.4 |
| 2003 | 26.7°C | 20.3°C | 13.8°C | 31.5°C | 5.6°C | 102 mm | 72% | 0.7 m/s | 4.9 |
| 2002 | 29.8°C | 23.2°C | 16.5°C | 35.4°C | 11.7°C | 150 mm | 67% | 0.7 m/s | 4.2 |
| 2001 | 26.2°C | 19.6°C | 12.9°C | 31.8°C | 4.9°C | 83 mm | 65% | 0.7 m/s | 4.9 |
| 2000 | 28.4°C | 21.5°C | 14.5°C | 33.1°C | 5.1°C | 79 mm | 65% | 0.8 m/s | 4.4 |
| 1999 | 29.5°C | 21.6°C | 13.8°C | 35.1°C | 6.6°C | 41 mm | 46% | 0.8 m/s | 5.3 |
| 1998 | 32.4°C | 24.9°C | 17.4°C | 37.4°C | 9.7°C | 31 mm | 54% | 0.7 m/s | 5.1 |
| 1997 | 29.0°C | 21.9°C | 14.9°C | 35.1°C | 9.0°C | 83 mm | 62% | 0.8 m/s | 4.6 |
| 1996 | 26.5°C | 20.2°C | 14.0°C | 30.9°C | 6.0°C | 95 mm | 71% | 0.8 m/s | 4.4 |
| 1995 | 28.3°C | 21.5°C | 14.7°C | 32.9°C | 8.2°C | 70 mm | 67% | 0.7 m/s | 4.2 |
| 1994 | 27.2°C | 20.4°C | 13.6°C | 32.8°C | 7.9°C | 50 mm | 68% | 0.7 m/s | 4.7 |
| 1993 | 28.3°C | 21.6°C | 14.8°C | 35.0°C | 3.4°C | 98 mm | 65% | 0.8 m/s | 4.4 |
| 1992 | 27.6°C | 21.5°C | 15.3°C | 32.2°C | 3.7°C | 69 mm | 73% | 0.7 m/s | 3.9 |
| 1991 | 27.4°C | 21.4°C | 15.5°C | 34.4°C | 3.9°C | 77 mm | 70% | 0.6 m/s | 4.5 |
| 1990 | 28.8°C | 22.2°C | 15.6°C | 35.4°C | 4.8°C | 86 mm | 65% | 0.7 m/s | 4.8 |
| 1989 🌧️ | 24.8°C | 19.8°C | 14.7°C | 29.4°C | 4.0°C | 229 mm | 83% | 0.7 m/s | 4 |
| 1988 | 27.8°C | 21.3°C | 14.9°C | 32.7°C | 7.5°C | 107 mm | 73% | 0.7 m/s | 3.9 |
| 1987 | 27.5°C | 21.3°C | 15.2°C | 31.7°C | 9.5°C | 101 mm | 66% | 0.7 m/s | 4.3 |
| 1986 | 28.0°C | 22.2°C | 16.4°C | 31.9°C | 11.7°C | 84 mm | 75% | 0.8 m/s | 4.2 |
| 1985 | 28.2°C | 20.8°C | 13.3°C | 33.2°C | 6.2°C | 26 mm | 62% | 0.7 m/s | 4.9 |
| 1984 | 27.8°C | 20.3°C | 12.8°C | 33.9°C | 7.0°C | 29 mm | 60% | 0.7 m/s | 4.9 |
| 1983 | 28.0°C | 21.3°C | 14.6°C | 34.8°C | 3.5°C | 48 mm | 63% | 0.8 m/s | — |
| 1982 | 25.9°C | 19.8°C | 13.8°C | 30.1°C | 6.6°C | 75 mm | 74% | 0.7 m/s | — |
| 1981 | 27.0°C | 20.0°C | 13.0°C | 32.3°C | 6.1°C | 104 mm | 65% | 0.7 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 28.1°C with lows near 15.2°C (mean 21.7°C), based on 45 years of NASA POWER data.
September averages 89 mm of rainfall in Knoxville, one of the drier months. The wettest on record was 229 mm in 1989.
The hottest September reached 37.5°C in 2011. The coldest dipped to 3.4°C in 1993.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.5°C. Daytime highs moved from 27.4°C to 28°C and overnight lows from 13.5°C to 15.7°C over the same span.
September is one of the warmer months of the year in Knoxville and one of the drier months, so plan for around 28.1°C daytime highs and 15.2°C at night.
Not quite — September is the 9th coolest month in Knoxville, averaging 21.7°C.
For September in Knoxville, pack light layers you can adjust through the day, with typical highs of 28.1°C and lows of 15.2°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 68% — moderately humid.
Average wind speed in September is 0.7 m/s. The windiest September on record averaged 0.8 m/s (1983).
The wettest September on record was 1989 with 229 mm. On average, September sees 89 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 Knoxville 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.
