September is one of the warmer months of the year in Richland, with average highs near 26.2°C and lows around 11.7°C (mean 19°C). It is one of the drier months, averaging 11 mm of rainfall and 47% relative humidity across the period.
September is one of the warmer months of the year in Richland. Across 45 years of records, the warmest September in Richland was 1990 — when the month averaged 21.6°C — while the coldest was 1985 at 14.9°C. Typical September days reach 26.2°C with nights near 11.7°C. The long-term trend is warming, about 0.5°C per decade.
September is one of the drier months in Richland, averaging 11 mm of rainfall. The wettest September on record was 2013 with 42 mm, while the driest were 1990 and 1999 at 0 mm.
Relative humidity in Richland during September averages 47%. The most humid September was 2010 at 56%, and the least humid was 1987 at 38%.
September receives about 4.7 kWh/m²/day of solar energy in Richland. 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 Richland during September is 2 m/s. The windiest September was 2013 at 2.5 m/s, while the calmest were 1990 and 1998 at 1.5 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 17.5°C | 19.4°C | 19.1°C | 19.2°C | 20.2°C | +2.7°C |
| Avg High | 24.6°C | 26.9°C | 26.4°C | 26.1°C | 27.3°C | +2.7°C |
| Avg Low | 10.3°C | 11.8°C | 11.7°C | 12.2°C | 13.0°C | +2.7°C |
| Avg Rain | 17 mm | 8 mm | 9 mm | 12 mm | 10 mm | -7 mm |
September temperatures in Richland have risen by about 3.5°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 0.4°C (1985) to a record high of 39.4°C (1988).
Rainfall in September is one of the drier months, averaging 11 mm, with a wettest year of 42 mm.
One of the best times to visit Richland
September is one of the best times to visit Richland. Expect days averaging 26.2°C and nights around 11.7°C (mean 19°C) — warmer than Richland's yearly average — with low rainfall (11 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 | 28.4°C | 20.8°C | 13.1°C | 38.0°C | 5.3°C | 7 mm | 52% | 1.7 m/s | 4.5 |
| 2024 | 27.3°C | 20.0°C | 12.7°C | 38.5°C | 3.6°C | 5 mm | 50% | 1.9 m/s | 4.6 |
| 2023 | 25.9°C | 19.3°C | 12.8°C | 34.2°C | 6.8°C | 12 mm | 49% | 1.9 m/s | 4.5 |
| 2022 | 28.3°C | 21.0°C | 13.7°C | 37.7°C | 10.0°C | 8 mm | 44% | 1.9 m/s | 4.6 |
| 2021 | 26.4°C | 19.4°C | 12.4°C | 34.5°C | 7.2°C | 23 mm | 46% | 2 m/s | 4.6 |
| 2020 | 27.5°C | 20.4°C | 13.3°C | 37.2°C | 8.6°C | 6 mm | 45% | 2 m/s | 4.3 |
| 2019 | 24.3°C | 18.2°C | 12.1°C | 32.6°C | 1.2°C | 22 mm | 56% | 2.2 m/s | 4.2 |
| 2018 | 25.1°C | 18.1°C | 11.1°C | 32.7°C | 7.3°C | 0 mm | 44% | 2.1 m/s | 5 |
| 2017 | 26.1°C | 19.7°C | 13.2°C | 38.3°C | 5.9°C | 10 mm | 48% | 1.9 m/s | 4.2 |
| 2016 | 25.0°C | 18.2°C | 11.3°C | 32.2°C | 6.7°C | 8 mm | 48% | 2.3 m/s | 4.8 |
| 2015 | 25.2°C | 18.3°C | 11.4°C | 35.7°C | 6.6°C | 8 mm | 45% | 1.9 m/s | 4.8 |
| 2014 | 27.1°C | 19.7°C | 12.3°C | 33.1°C | 5.9°C | 8 mm | 45% | 2.4 m/s | 4.9 |
| 2013 🌧️ | 26.0°C | 19.8°C | 13.5°C | 35.4°C | 7.3°C | 42 mm | 55% | 2.5 m/s | 4.2 |
| 2012 | 27.8°C | 20.0°C | 12.2°C | 34.5°C | 8.3°C | 1 mm | 41% | 1.6 m/s | 5 |
| 2011 | 28.9°C | 21.1°C | 13.3°C | 36.7°C | 7.5°C | 2 mm | 42% | 2 m/s | 4.9 |
| 2010 | 25.1°C | 18.5°C | 11.8°C | 32.5°C | 7.2°C | 20 mm | 56% | 2.1 m/s | 4.5 |
| 2009 | 28.1°C | 20.6°C | 13.1°C | 35.6°C | 4.9°C | 4 mm | 42% | 2.2 m/s | 5 |
| 2008 | 26.7°C | 19.1°C | 11.4°C | 33.9°C | 5.6°C | 6 mm | 42% | 2 m/s | 5 |
| 2007 | 25.5°C | 18.3°C | 11.0°C | 33.0°C | 3.3°C | 14 mm | 46% | 2.1 m/s | 4.9 |
| 2006 | 26.9°C | 19.4°C | 11.9°C | 36.0°C | 6.1°C | 6 mm | 44% | 1.7 m/s | 4.7 |
| 2005 | 24.8°C | 17.8°C | 10.8°C | 32.5°C | 5.8°C | 18 mm | 45% | 1.9 m/s | 4.8 |
| 2004 | 24.6°C | 17.8°C | 11.0°C | 30.2°C | 6.3°C | 7 mm | 54% | 2 m/s | 4.6 |
| 2003 | 28.0°C | 20.6°C | 13.2°C | 38.9°C | 6.3°C | 6 mm | 43% | 2 m/s | 4.8 |
| 2002 | 26.7°C | 19.1°C | 11.4°C | 35.4°C | 6.4°C | 2 mm | 41% | 2 m/s | 4.9 |
| 2001 | 28.1°C | 20.4°C | 12.6°C | 34.5°C | 8.0°C | 3 mm | 41% | 1.9 m/s | 5.1 |
| 2000 | 24.6°C | 17.6°C | 10.5°C | 33.4°C | 1.0°C | 21 mm | 50% | 2.3 m/s | 4.3 |
| 1999 | 26.5°C | 18.5°C | 10.5°C | 33.2°C | 3.2°C | 0 mm | 39% | 2 m/s | 5.2 |
| 1998 | 28.9°C | 21.3°C | 13.8°C | 38.2°C | 9.2°C | 8 mm | 47% | 1.5 m/s | 4.9 |
| 1997 | 25.8°C | 19.0°C | 12.3°C | 33.0°C | 7.3°C | 22 mm | 55% | 2.3 m/s | 4.4 |
| 1996 | 24.1°C | 16.9°C | 9.6°C | 33.8°C | 4.1°C | 8 mm | 51% | 2 m/s | 4.6 |
| 1995 | 26.8°C | 19.6°C | 12.4°C | 34.7°C | 6.0°C | 24 mm | 50% | 2 m/s | 4.9 |
| 1994 | 28.4°C | 20.6°C | 12.9°C | 32.7°C | 8.0°C | 5 mm | 43% | 1.8 m/s | 4.9 |
| 1993 | 26.8°C | 19.0°C | 11.2°C | 35.1°C | 3.9°C | 2 mm | 44% | 1.6 m/s | 5.2 |
| 1992 | 23.8°C | 17.0°C | 10.2°C | 30.4°C | 5.8°C | 12 mm | 49% | 2.2 m/s | 4.6 |
| 1991 | 27.9°C | 20.0°C | 12.0°C | 33.8°C | 7.7°C | 0 mm | 41% | 1.8 m/s | 5.2 |
| 1990 🔥 | 30.2°C | 21.6°C | 13.1°C | 35.5°C | 7.4°C | 0 mm | 42% | 1.5 m/s | 5.3 |
| 1989 | 26.8°C | 18.8°C | 10.9°C | 32.3°C | 6.7°C | 2 mm | 42% | 1.9 m/s | 5.1 |
| 1988 | 26.3°C | 18.7°C | 11.1°C | 39.4°C | 5.8°C | 11 mm | 42% | 2 m/s | 4.7 |
| 1987 | 28.6°C | 20.7°C | 12.7°C | 38.3°C | 6.4°C | 1 mm | 38% | 1.7 m/s | 5.1 |
| 1986 | 22.0°C | 15.9°C | 9.8°C | 33.2°C | 5.7°C | 33 mm | 55% | 2.1 m/s | 4.4 |
| 1985 ❄️ | 21.4°C | 14.9°C | 8.4°C | 28.6°C | 0.4°C | 28 mm | 52% | 2.2 m/s | 4.4 |
| 1984 | 23.3°C | 16.2°C | 9.0°C | 32.7°C | 0.6°C | 18 mm | 51% | 2.3 m/s | 4.6 |
| 1983 | 23.1°C | 16.0°C | 8.9°C | 28.5°C | 1.6°C | 14 mm | 51% | 2.2 m/s | — |
| 1982 | 24.2°C | 17.4°C | 10.6°C | 31.6°C | 4.0°C | 30 mm | 54% | 2.4 m/s | — |
| 1981 | 26.1°C | 18.7°C | 11.2°C | 36.1°C | 5.2°C | 15 mm | 47% | 2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 26.2°C with lows near 11.7°C (mean 19°C), based on 45 years of NASA POWER data.
September averages 11 mm of rainfall in Richland, one of the drier months. The wettest on record was 42 mm in 2013.
The hottest September reached 39.4°C in 1988. The coldest dipped to 0.4°C in 1985.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 3.5°C. Daytime highs moved from 23.6°C to 27.3°C and overnight lows from 9.6°C to 12.9°C over the same span.
September is one of the warmer months of the year in Richland and one of the drier months, so plan for around 26.2°C daytime highs and 11.7°C at night.
Not quite — September is the 9th coolest month in Richland, averaging 19°C.
For September in Richland, pack light layers you can adjust through the day, with typical highs of 26.2°C and lows of 11.7°C.
Relative humidity in September averages 47% — relatively dry.
Average wind speed in September is 2 m/s. The windiest September on record averaged 2.5 m/s (2013).
The wettest September on record was 2013 with 42 mm. On average, September sees 11 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 Richland 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.
