September is one of the warmer months of the year in Decatur, with average highs near 29.5°C and lows around 17°C (mean 23.3°C). It is one of the drier months, averaging 97 mm of rainfall and 68% relative humidity across the period.
September is one of the warmer months of the year in Decatur. Across 45 years of records, the warmest September in Decatur was 2019 — when the month averaged 27.7°C — while the coldest was 2011 at 20.7°C. Typical September days reach 29.5°C with nights near 17°C. The long-term trend is warming, about 0.4°C per decade.
September is one of the drier months in Decatur, averaging 97 mm of rainfall. The wettest September on record was 1988 with 230 mm, while the driest was 1984 at 9 mm.
Relative humidity in Decatur during September averages 68%. The most humid September was 1989 at 83%, and the least humid was 1999 at 44%.
September receives about 4.8 kWh/m²/day of solar energy in Decatur. The sunniest September was 2019 at 5.7 kWh/m²/day, and the cloudiest was 2009 at 3.8.
Average wind speed in Decatur during September is 0.9 m/s. The windiest Septembers were 2000 and 2004 at 1.2 m/s, while the calmest were 2021, 2023 and 2025, among others at 0.8 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 22.3°C | 23.3°C | 23.1°C | 24.0°C | 23.3°C | +1°C |
| Avg High | 28.5°C | 29.9°C | 29.2°C | 30.2°C | 29.5°C | +1°C |
| Avg Low | 16.2°C | 16.7°C | 17.0°C | 17.7°C | 17.1°C | +0.9°C |
| Avg Rain | 99 mm | 93 mm | 107 mm | 87 mm | 102 mm | +3 mm |
September temperatures in Decatur have risen by about 1.3°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 4.2°C (2001) to a record high of 39.2°C (1990).
Rainfall in September is one of the drier months, averaging 97 mm, with a wettest year of 230 mm.
One of the best times to visit Decatur
September is one of the best times to visit Decatur. Expect days averaging 29.5°C and nights around 17°C (mean 23.3°C) — warmer than Decatur'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 | 31.2°C | 24.5°C | 17.7°C | 34.7°C | 11.9°C | 93 mm | 64% | 0.8 m/s | 5.1 |
| 2024 | 29.7°C | 23.9°C | 18.1°C | 34.4°C | 11.7°C | 155 mm | 69% | 1.1 m/s | 4.3 |
| 2023 | 31.2°C | 24.3°C | 17.4°C | 33.8°C | 13.0°C | 30 mm | 64% | 0.8 m/s | 5.1 |
| 2022 | 29.3°C | 22.7°C | 16.1°C | 36.3°C | 8.0°C | 82 mm | 67% | 0.9 m/s | 5.2 |
| 2021 | 27.2°C | 22.0°C | 16.8°C | 30.1°C | 9.0°C | 137 mm | 79% | 0.8 m/s | 4.9 |
| 2020 | 28.2°C | 22.5°C | 16.7°C | 32.4°C | 8.0°C | 117 mm | 75% | 1 m/s | 4.6 |
| 2019 🔥 | 34.8°C | 27.7°C | 20.6°C | 37.8°C | 15.4°C | 17 mm | 59% | 0.8 m/s | 5.7 |
| 2018 | 32.2°C | 26.4°C | 20.7°C | 36.6°C | 16.5°C | 141 mm | 72% | 0.9 m/s | 4.5 |
| 2017 | 27.9°C | 22.0°C | 16.1°C | 31.7°C | 9.8°C | 98 mm | 73% | 1 m/s | 5 |
| 2016 | 33.1°C | 26.2°C | 19.3°C | 36.6°C | 9.8°C | 21 mm | 60% | 0.9 m/s | 5.5 |
| 2015 | 29.4°C | 23.2°C | 17.0°C | 33.3°C | 9.5°C | 29 mm | 71% | 0.8 m/s | 4.8 |
| 2014 | 30.1°C | 24.1°C | 18.1°C | 34.0°C | 10.2°C | 36 mm | 71% | 0.8 m/s | 5 |
| 2013 | 29.0°C | 23.0°C | 16.9°C | 33.2°C | 10.5°C | 92 mm | 74% | 0.8 m/s | 5.2 |
| 2012 | 27.7°C | 21.7°C | 15.7°C | 34.1°C | 6.4°C | 187 mm | 73% | 0.9 m/s | 4.8 |
| 2011 ❄️ | 26.0°C | 20.7°C | 15.3°C | 37.5°C | 9.2°C | 211 mm | 76% | 1 m/s | 4.2 |
| 2010 | 32.2°C | 24.8°C | 17.5°C | 36.7°C | 9.8°C | 41 mm | 58% | 0.9 m/s | 5.4 |
| 2009 | 27.2°C | 22.8°C | 18.5°C | 30.7°C | 8.1°C | 203 mm | 82% | 0.8 m/s | 3.8 |
| 2008 | 29.2°C | 23.2°C | 17.2°C | 33.4°C | 11.1°C | 29 mm | 70% | 1.1 m/s | 4.7 |
| 2007 | 30.9°C | 24.5°C | 18.1°C | 34.8°C | 9.4°C | 69 mm | 64% | 0.9 m/s | 5.1 |
| 2006 | 28.7°C | 22.1°C | 15.4°C | 33.4°C | 7.1°C | 104 mm | 65% | 1.1 m/s | 4.9 |
| 2005 | 31.8°C | 24.8°C | 17.8°C | 35.6°C | 8.4°C | 75 mm | 64% | 1 m/s | 5.3 |
| 2004 | 27.9°C | 22.2°C | 16.4°C | 33.5°C | 9.2°C | 142 mm | 75% | 1.2 m/s | 5 |
| 2003 | 29.1°C | 22.5°C | 15.9°C | 33.3°C | 5.8°C | 99 mm | 69% | 1 m/s | 5.3 |
| 2002 | 30.8°C | 25.1°C | 19.4°C | 37.1°C | 13.7°C | 164 mm | 69% | 1 m/s | 4.2 |
| 2001 | 26.6°C | 21.0°C | 15.3°C | 31.4°C | 4.2°C | 110 mm | 72% | 1 m/s | 4.9 |
| 2000 | 29.5°C | 23.0°C | 16.4°C | 35.5°C | 6.5°C | 73 mm | 62% | 1.2 m/s | 4.5 |
| 1999 | 31.6°C | 23.9°C | 16.2°C | 38.7°C | 7.3°C | 25 mm | 44% | 1 m/s | 5.2 |
| 1998 | 33.3°C | 26.2°C | 19.0°C | 38.4°C | 11.8°C | 28 mm | 55% | 0.9 m/s | 5.2 |
| 1997 | 30.1°C | 23.4°C | 16.7°C | 35.5°C | 11.8°C | 129 mm | 65% | 0.9 m/s | 5 |
| 1996 | 27.7°C | 21.6°C | 15.4°C | 32.6°C | 7.0°C | 156 mm | 73% | 1 m/s | 4.6 |
| 1995 | 29.4°C | 22.9°C | 16.3°C | 35.8°C | 8.0°C | 116 mm | 66% | 1 m/s | 4.5 |
| 1994 | 28.6°C | 22.0°C | 15.4°C | 32.8°C | 8.6°C | 93 mm | 71% | 0.9 m/s | 4.9 |
| 1993 | 29.6°C | 22.7°C | 15.9°C | 36.2°C | 6.3°C | 103 mm | 66% | 1 m/s | 4.5 |
| 1992 | 26.9°C | 21.7°C | 16.5°C | 31.2°C | 6.0°C | 121 mm | 80% | 1 m/s | 4.1 |
| 1991 | 29.9°C | 23.6°C | 17.4°C | 36.1°C | 5.8°C | 86 mm | 66% | 0.9 m/s | 4.9 |
| 1990 | 31.7°C | 25.0°C | 18.2°C | 39.2°C | 5.9°C | 77 mm | 60% | 0.9 m/s | 5.1 |
| 1989 | 26.2°C | 21.2°C | 16.2°C | 31.0°C | 6.4°C | 216 mm | 83% | 0.9 m/s | 4.1 |
| 1988 🌧️ | 27.9°C | 22.7°C | 17.4°C | 32.0°C | 9.8°C | 230 mm | 79% | 1 m/s | 3.9 |
| 1987 | 28.8°C | 22.6°C | 16.4°C | 33.5°C | 10.9°C | 122 mm | 66% | 0.9 m/s | 4.6 |
| 1986 | 29.2°C | 23.7°C | 18.3°C | 33.3°C | 13.0°C | 109 mm | 77% | 0.9 m/s | 4.5 |
| 1985 | 27.6°C | 21.4°C | 15.2°C | 31.8°C | 6.5°C | 77 mm | 70% | 1 m/s | 5 |
| 1984 | 30.2°C | 22.6°C | 15.1°C | 36.5°C | 9.9°C | 9 mm | 57% | 1.1 m/s | 5 |
| 1983 | 28.9°C | 22.6°C | 16.4°C | 35.6°C | 5.2°C | 65 mm | 66% | 0.9 m/s | — |
| 1982 | 29.3°C | 22.6°C | 16.0°C | 33.9°C | 7.6°C | 33 mm | 65% | 0.9 m/s | — |
| 1981 | 28.7°C | 21.7°C | 14.6°C | 32.0°C | 6.8°C | 35 mm | 65% | 0.9 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 29.5°C with lows near 17°C (mean 23.3°C), based on 45 years of NASA POWER data.
September averages 97 mm of rainfall in Decatur, one of the drier months. The wettest on record was 230 mm in 1988.
The hottest September reached 39.2°C in 1990. The coldest dipped to 4.2°C in 2001.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.3°C. Daytime highs moved from 28.9°C to 29.7°C and overnight lows from 15.5°C to 17.2°C over the same span.
September is one of the warmer months of the year in Decatur and one of the drier months, so plan for around 29.5°C daytime highs and 17°C at night.
Not quite — September is the 9th coolest month in Decatur, averaging 23.3°C.
For September in Decatur, pack light layers you can adjust through the day, with typical highs of 29.5°C and lows of 17°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 68% — moderately humid.
Average wind speed in September is 0.9 m/s. The windiest September on record averaged 1.2 m/s (2000).
The wettest September on record was 1988 with 230 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 Decatur 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.
