September is one of the warmer months of the year in Normal, with average highs near 25.5°C and lows around 12.9°C (mean 19.2°C). It is about average for rainfall, averaging 77 mm of rainfall and 70% relative humidity across the period.
September is one of the warmer months of the year in Normal. Across 45 years of records, the warmest September in Normal was 2005 — when the month averaged 22.2°C — while the coldest was 1993 at 15°C. Typical September days reach 25.5°C with nights near 12.9°C. The long-term trend is warming, about 0.5°C per decade.
September is about average for rainfall in Normal, averaging 77 mm of rainfall. The wettest September on record was 2008 with 265 mm, while the driest was 2004 at 25 mm.
Relative humidity in Normal during September averages 70%. The most humid September was 1993 at 84%, and the least humid was 1988 at 56%.
September receives about 4.5 kWh/m²/day of solar energy in Normal. The sunniest September was 2004 at 5.3 kWh/m²/day, and the cloudiest was 1993 at 3.4.
Average wind speed in Normal during September is 2.5 m/s. The windiest September was 1985 at 3.3 m/s, while the calmest was 2025 at 1.8 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 18.8°C | 18.2°C | 19.3°C | 19.8°C | 20.3°C | +1.5°C |
| Avg High | 25.1°C | 24.5°C | 25.7°C | 25.8°C | 26.9°C | +1.8°C |
| Avg Low | 12.6°C | 11.9°C | 12.9°C | 13.8°C | 13.7°C | +1.1°C |
| Avg Rain | 80 mm | 72 mm | 78 mm | 91 mm | 58 mm | -22 mm |
September temperatures in Normal have risen by about 2.1°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -0.2°C (1995) to a record high of 38.1°C (2011).
Rainfall in September is about average for rainfall, averaging 77 mm, with a wettest year of 265 mm.
One of the best times to visit Normal
September is one of the best times to visit Normal. Expect days averaging 25.5°C and nights around 12.9°C (mean 19.2°C) — warmer than Normal's yearly average — with moderate rainfall (77 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 | 28.7°C | 21.4°C | 14.1°C | 34.1°C | 6.9°C | 28 mm | 59% | 1.8 m/s | 5.1 |
| 2024 | 27.9°C | 20.9°C | 13.9°C | 33.6°C | 7.9°C | 48 mm | 61% | 2.3 m/s | 4.7 |
| 2023 | 27.0°C | 20.6°C | 14.3°C | 33.9°C | 8.3°C | 73 mm | 67% | 2.2 m/s | 4.2 |
| 2022 | 25.9°C | 19.5°C | 13.0°C | 34.0°C | 3.5°C | 51 mm | 69% | 2.5 m/s | 4.7 |
| 2021 | 26.8°C | 20.5°C | 14.2°C | 31.4°C | 8.0°C | 70 mm | 71% | 2.8 m/s | 4.9 |
| 2020 | 25.0°C | 18.8°C | 12.5°C | 31.1°C | 4.6°C | 78 mm | 73% | 2.6 m/s | 4.1 |
| 2019 | 27.6°C | 22.0°C | 16.4°C | 32.1°C | 11.7°C | 141 mm | 77% | 2.6 m/s | 4.4 |
| 2018 | 27.0°C | 21.0°C | 15.0°C | 33.5°C | 4.9°C | 77 mm | 74% | 2.5 m/s | 4.4 |
| 2017 | 27.8°C | 20.9°C | 14.1°C | 34.1°C | 7.8°C | 29 mm | 64% | 2.3 m/s | 5 |
| 2016 | 25.3°C | 20.4°C | 15.6°C | 31.0°C | 9.2°C | 99 mm | 82% | 2.5 m/s | 4.6 |
| 2015 | 25.9°C | 20.2°C | 14.6°C | 32.1°C | 6.6°C | 104 mm | 77% | 2.5 m/s | 4.6 |
| 2014 | 23.7°C | 17.8°C | 11.9°C | 31.0°C | 5.2°C | 128 mm | 75% | 2.3 m/s | 4.7 |
| 2013 | 27.8°C | 20.9°C | 13.9°C | 35.9°C | 7.4°C | 35 mm | 66% | 2.5 m/s | 5 |
| 2012 | 24.2°C | 18.2°C | 12.2°C | 31.3°C | 3.4°C | 109 mm | 71% | 2.6 m/s | 4.7 |
| 2011 | 23.7°C | 17.7°C | 11.6°C | 38.1°C | 4.5°C | 82 mm | 69% | 2.9 m/s | 4.2 |
| 2010 | 24.5°C | 18.7°C | 12.9°C | 30.3°C | 7.3°C | 106 mm | 76% | 2.9 m/s | 4.7 |
| 2009 | 23.2°C | 17.9°C | 12.6°C | 26.4°C | 7.8°C | 57 mm | 81% | 2.1 m/s | 4.4 |
| 2008 🌧️ | 24.1°C | 18.6°C | 13.2°C | 31.5°C | 7.5°C | 265 mm | 81% | 2.1 m/s | 4 |
| 2007 | 28.0°C | 21.1°C | 14.2°C | 33.7°C | 3.2°C | 38 mm | 65% | 2.7 m/s | 5.2 |
| 2006 | 23.7°C | 17.7°C | 11.7°C | 30.3°C | 4.2°C | 67 mm | 73% | 2.6 m/s | 4 |
| 2005 🔥 | 28.9°C | 22.2°C | 15.5°C | 34.7°C | 4.6°C | 86 mm | 64% | 2.5 m/s | 4.6 |
| 2004 | 26.8°C | 20.1°C | 13.3°C | 30.3°C | 7.0°C | 25 mm | 67% | 2.4 m/s | 5.3 |
| 2003 | 24.0°C | 17.7°C | 11.5°C | 28.9°C | 2.8°C | 62 mm | 70% | 2.6 m/s | 4.7 |
| 2002 | 27.2°C | 20.4°C | 13.5°C | 32.8°C | 4.6°C | 33 mm | 67% | 2.2 m/s | 4.8 |
| 2001 | 24.7°C | 18.0°C | 11.3°C | 31.3°C | 2.6°C | 74 mm | 69% | 2.7 m/s | 4.8 |
| 2000 | 26.4°C | 19.3°C | 12.2°C | 35.8°C | 3.5°C | 78 mm | 64% | 3.1 m/s | 4.5 |
| 1999 | 26.4°C | 18.8°C | 11.1°C | 34.2°C | 4.3°C | 47 mm | 57% | 2.6 m/s | 5 |
| 1998 | 27.4°C | 20.8°C | 14.3°C | 34.0°C | 7.6°C | 40 mm | 69% | 2.4 m/s | 4.6 |
| 1997 | 24.7°C | 18.5°C | 12.3°C | 30.7°C | 7.0°C | 72 mm | 71% | 2.4 m/s | 4.6 |
| 1996 | 25.1°C | 18.6°C | 12.0°C | 31.8°C | 5.3°C | 60 mm | 66% | 2.4 m/s | 4.5 |
| 1995 | 23.9°C | 17.1°C | 10.2°C | 30.0°C | -0.2°C | 29 mm | 65% | 2.5 m/s | 4.5 |
| 1994 | 25.1°C | 18.7°C | 12.3°C | 32.6°C | 6.7°C | 54 mm | 68% | 2.3 m/s | 4.5 |
| 1993 ❄️ | 19.8°C | 15.0°C | 10.1°C | 25.2°C | 0.1°C | 196 mm | 84% | 2.7 m/s | 3.4 |
| 1992 | 23.1°C | 17.0°C | 10.8°C | 29.0°C | 0.7°C | 113 mm | 75% | 2.6 m/s | 4.3 |
| 1991 | 25.0°C | 18.7°C | 12.4°C | 32.6°C | 0.9°C | 70 mm | 65% | 2.5 m/s | 4.5 |
| 1990 | 24.7°C | 18.9°C | 13.0°C | 33.2°C | 2.6°C | 37 mm | 74% | 2.4 m/s | 4.3 |
| 1989 | 22.2°C | 16.5°C | 10.7°C | 29.3°C | 0.7°C | 131 mm | 77% | 2.4 m/s | 4.4 |
| 1988 | 28.3°C | 21.0°C | 13.6°C | 33.4°C | 7.7°C | 50 mm | 56% | 2.9 m/s | 4.3 |
| 1987 | 25.8°C | 19.3°C | 12.9°C | 31.9°C | 7.5°C | 44 mm | 68% | 2.5 m/s | 4.4 |
| 1986 | 26.1°C | 20.5°C | 14.8°C | 30.5°C | 5.9°C | 209 mm | 75% | 2.8 m/s | 3.8 |
| 1985 | 25.5°C | 19.4°C | 13.2°C | 33.0°C | 3.9°C | 42 mm | 68% | 3.3 m/s | 4.2 |
| 1984 | 24.5°C | 18.1°C | 11.8°C | 36.6°C | 0.6°C | 77 mm | 65% | 3.1 m/s | 3.9 |
| 1983 | 26.6°C | 19.6°C | 12.6°C | 35.5°C | 1.3°C | 75 mm | 62% | 2.7 m/s | — |
| 1982 | 24.2°C | 18.3°C | 12.4°C | 29.6°C | 4.2°C | 39 mm | 74% | 2.5 m/s | — |
| 1981 | 22.5°C | 16.9°C | 11.3°C | 28.5°C | 3.7°C | 59 mm | 79% | 2.7 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 25.5°C with lows near 12.9°C (mean 19.2°C), based on 45 years of NASA POWER data.
September averages 77 mm of rainfall in Normal, about average for rainfall. The wettest on record was 265 mm in 2008.
The hottest September reached 38.1°C in 2011. The coldest dipped to -0.2°C in 1995.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2.1°C. Daytime highs moved from 24.7°C to 27.3°C and overnight lows from 12.3°C to 13.9°C over the same span.
September is one of the warmer months of the year in Normal and about average for rainfall, so plan for around 25.5°C daytime highs and 12.9°C at night.
Not quite — September is the 9th coolest month in Normal, averaging 19.2°C.
For September in Normal, pack light layers you can adjust through the day, with typical highs of 25.5°C and lows of 12.9°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 70% — moderately humid.
Average wind speed in September is 2.5 m/s. The windiest September on record averaged 3.3 m/s (1985).
The wettest September on record was 2008 with 265 mm. On average, September sees 77 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 Normal 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.
