September is one of the warmer months of the year in Kennewick, with average highs near 25.9°C and lows around 12°C (mean 19°C). It is one of the drier months, averaging 13 mm of rainfall and 48% relative humidity across the period.
September is one of the warmer months of the year in Kennewick. Across 45 years of records, the warmest September in Kennewick was 1990 — when the month averaged 21.3°C — while the coldest was 1985 at 15°C. Typical September days reach 25.9°C with nights near 12°C. The long-term trend is warming, about 0.5°C per decade.
September is one of the drier months in Kennewick, averaging 13 mm of rainfall. The wettest September on record was 2013 with 51 mm, while the driest were 1991, 1999 and 2018 at 0 mm.
Relative humidity in Kennewick during September averages 48%. The most humid September was 2010 at 57%, and the least humid were 1987 and 1999 at 40%.
September receives about 4.7 kWh/m²/day of solar energy in Kennewick. The sunniest September was 1990 at 5.3 kWh/m²/day, and the cloudiest were 2013, 2017 and 2019 at 4.2.
Average wind speed in Kennewick during September is 2.3 m/s. The windiest September was 2013 at 2.8 m/s, while the calmest was 2012 at 1.9 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 17.4°C | 19.3°C | 19.0°C | 19.2°C | 20.2°C | +2.8°C |
| Avg High | 24.4°C | 26.6°C | 26.1°C | 25.8°C | 27.1°C | +2.7°C |
| Avg Low | 10.4°C | 12.0°C | 12.0°C | 12.5°C | 13.4°C | +3°C |
| Avg Rain | 19 mm | 9 mm | 9 mm | 14 mm | 13 mm | -6 mm |
September temperatures in Kennewick have risen by about 3.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 0.5°C (1984) to a record high of 38.3°C (1987).
Rainfall in September is one of the drier months, averaging 13 mm, with a wettest year of 51 mm.
One of the best times to visit Kennewick
September is one of the best times to visit Kennewick. Expect days averaging 25.9°C and nights around 12°C (mean 19°C) — warmer than Kennewick's yearly average — with low rainfall (13 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 | 28.0°C | 20.9°C | 13.7°C | 37.2°C | 6.8°C | 13 mm | 53% | 2 m/s | 4.5 |
| 2024 | 27.0°C | 20.0°C | 13.1°C | 37.1°C | 4.2°C | 8 mm | 51% | 2.3 m/s | 4.6 |
| 2023 | 25.7°C | 19.4°C | 13.2°C | 32.5°C | 8.2°C | 16 mm | 50% | 2.3 m/s | 4.5 |
| 2022 | 27.8°C | 20.9°C | 14.0°C | 37.1°C | 10.3°C | 8 mm | 45% | 2.3 m/s | 4.6 |
| 2021 | 26.4°C | 19.6°C | 12.7°C | 33.8°C | 7.3°C | 26 mm | 46% | 2.2 m/s | 4.6 |
| 2020 | 27.4°C | 20.6°C | 13.8°C | 37.3°C | 9.3°C | 5 mm | 45% | 2.4 m/s | 4.3 |
| 2019 | 23.9°C | 18.2°C | 12.6°C | 32.5°C | 1.4°C | 22 mm | 57% | 2.6 m/s | 4.2 |
| 2018 | 24.9°C | 18.2°C | 11.4°C | 32.4°C | 7.5°C | 0 mm | 45% | 2.2 m/s | 5 |
| 2017 | 25.7°C | 19.5°C | 13.4°C | 37.5°C | 6.0°C | 14 mm | 49% | 2.2 m/s | 4.2 |
| 2016 | 24.7°C | 18.1°C | 11.5°C | 31.7°C | 7.5°C | 11 mm | 50% | 2.5 m/s | 4.8 |
| 2015 | 25.2°C | 18.3°C | 11.4°C | 35.4°C | 6.7°C | 6 mm | 46% | 2.1 m/s | 4.8 |
| 2014 | 26.9°C | 19.8°C | 12.8°C | 32.6°C | 7.7°C | 7 mm | 46% | 2.5 m/s | 4.9 |
| 2013 🌧️ | 25.6°C | 19.6°C | 13.7°C | 34.5°C | 7.8°C | 51 mm | 56% | 2.8 m/s | 4.2 |
| 2012 | 27.5°C | 20.0°C | 12.6°C | 34.5°C | 8.6°C | 1 mm | 42% | 1.9 m/s | 5 |
| 2011 | 28.5°C | 21.1°C | 13.7°C | 36.5°C | 8.2°C | 2 mm | 44% | 2.1 m/s | 4.9 |
| 2010 | 25.2°C | 18.7°C | 12.3°C | 31.9°C | 8.5°C | 25 mm | 57% | 2.1 m/s | 4.5 |
| 2009 | 27.7°C | 20.4°C | 13.1°C | 36.7°C | 5.5°C | 4 mm | 44% | 2.5 m/s | 5 |
| 2008 | 26.4°C | 18.9°C | 11.4°C | 32.7°C | 7.2°C | 7 mm | 44% | 2.1 m/s | 5 |
| 2007 | 25.2°C | 18.4°C | 11.5°C | 33.1°C | 4.9°C | 13 mm | 47% | 2.5 m/s | 4.9 |
| 2006 | 26.8°C | 19.4°C | 12.1°C | 36.7°C | 6.3°C | 7 mm | 44% | 2.1 m/s | 4.7 |
| 2005 | 24.7°C | 18.0°C | 11.2°C | 32.0°C | 5.2°C | 12 mm | 44% | 2.3 m/s | 4.8 |
| 2004 | 24.3°C | 17.8°C | 11.3°C | 29.5°C | 7.2°C | 10 mm | 56% | 2.4 m/s | 4.6 |
| 2003 | 27.5°C | 20.3°C | 13.2°C | 37.5°C | 7.0°C | 10 mm | 44% | 2.2 m/s | 4.8 |
| 2002 | 26.2°C | 18.9°C | 11.7°C | 35.2°C | 6.8°C | 3 mm | 42% | 2.3 m/s | 4.9 |
| 2001 | 27.7°C | 20.5°C | 13.2°C | 34.1°C | 8.2°C | 3 mm | 42% | 2.2 m/s | 5.1 |
| 2000 | 24.3°C | 17.6°C | 10.9°C | 32.5°C | 1.7°C | 24 mm | 52% | 2.5 m/s | 4.3 |
| 1999 | 26.3°C | 18.4°C | 10.6°C | 32.9°C | 3.8°C | 0 mm | 40% | 2.2 m/s | 5.2 |
| 1998 | 28.1°C | 21.1°C | 14.1°C | 37.5°C | 9.2°C | 12 mm | 49% | 2.1 m/s | 4.9 |
| 1997 | 25.9°C | 19.2°C | 12.6°C | 33.1°C | 7.5°C | 22 mm | 54% | 2.4 m/s | 4.4 |
| 1996 | 24.0°C | 17.1°C | 10.3°C | 32.2°C | 4.8°C | 10 mm | 53% | 2.5 m/s | 4.6 |
| 1995 | 26.4°C | 19.6°C | 12.8°C | 34.2°C | 6.5°C | 20 mm | 51% | 2.2 m/s | 4.9 |
| 1994 | 27.9°C | 20.4°C | 12.8°C | 32.8°C | 8.2°C | 6 mm | 44% | 2.1 m/s | 4.9 |
| 1993 | 26.7°C | 19.0°C | 11.3°C | 35.0°C | 4.6°C | 1 mm | 45% | 2 m/s | 5.2 |
| 1992 | 23.9°C | 17.3°C | 10.7°C | 30.4°C | 6.8°C | 14 mm | 50% | 2.6 m/s | 4.6 |
| 1991 | 27.7°C | 19.9°C | 12.2°C | 33.7°C | 8.5°C | 0 mm | 42% | 2 m/s | 5.2 |
| 1990 🔥 | 29.5°C | 21.3°C | 13.1°C | 34.8°C | 8.4°C | 1 mm | 44% | 2 m/s | 5.3 |
| 1989 | 26.4°C | 18.7°C | 11.0°C | 32.0°C | 7.3°C | 3 mm | 44% | 2.1 m/s | 5.1 |
| 1988 | 26.0°C | 18.6°C | 11.1°C | 38.2°C | 5.4°C | 11 mm | 44% | 2.3 m/s | 4.7 |
| 1987 | 28.2°C | 20.5°C | 12.8°C | 38.3°C | 7.2°C | 1 mm | 40% | 2.2 m/s | 5.1 |
| 1986 | 21.8°C | 15.9°C | 10.0°C | 33.0°C | 6.2°C | 32 mm | 55% | 2.4 m/s | 4.4 |
| 1985 ❄️ | 21.4°C | 15.0°C | 8.6°C | 28.4°C | 0.5°C | 31 mm | 54% | 2.4 m/s | 4.4 |
| 1984 | 23.3°C | 16.2°C | 9.1°C | 33.6°C | 0.5°C | 20 mm | 52% | 2.4 m/s | 4.6 |
| 1983 | 22.8°C | 16.0°C | 9.2°C | 28.2°C | 1.5°C | 14 mm | 53% | 2.4 m/s | — |
| 1982 | 24.0°C | 17.3°C | 10.7°C | 31.5°C | 4.5°C | 41 mm | 55% | 2.5 m/s | — |
| 1981 | 25.9°C | 18.7°C | 11.5°C | 35.5°C | 5.5°C | 20 mm | 48% | 2.2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 25.9°C with lows near 12°C (mean 19°C), based on 45 years of NASA POWER data.
September averages 13 mm of rainfall in Kennewick, one of the drier months. The wettest on record was 51 mm in 2013.
The hottest September reached 38.3°C in 1987. The coldest dipped to 0.5°C in 1984.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 3.6°C. Daytime highs moved from 23.5°C to 27°C and overnight lows from 9.8°C to 13.3°C over the same span.
September is one of the warmer months of the year in Kennewick and one of the drier months, so plan for around 25.9°C daytime highs and 12°C at night.
Not quite — September is the 9th coolest month in Kennewick, averaging 19°C.
For September in Kennewick, pack light layers you can adjust through the day, with typical highs of 25.9°C and lows of 12°C.
Relative humidity in September averages 48% — relatively dry.
Average wind speed in September is 2.3 m/s. The windiest September on record averaged 2.8 m/s (2013).
The wettest September on record was 2013 with 51 mm. On average, September sees 13 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 Kennewick 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.
