September is one of the warmer months of the year in Naperville, with average highs near 24.3°C and lows around 12.5°C (mean 18.4°C). It is about average for rainfall, averaging 82 mm of rainfall and 72% relative humidity across the period.
September is one of the warmer months of the year in Naperville. Across 45 years of records, the warmest September in Naperville was 2005 — when the month averaged 21.5°C — while the coldest was 1993 at 14.4°C. Typical September days reach 24.3°C with nights near 12.5°C. The long-term trend is warming, about 0.6°C per decade.
September is about average for rainfall in Naperville, averaging 82 mm of rainfall. The wettest September on record was 2008 with 251 mm, while the driest was 2017 at 12 mm.
Relative humidity in Naperville during September averages 72%. The most humid September was 2019 at 84%, and the least humid was 2024 at 61%.
September receives about 4.4 kWh/m²/day of solar energy in Naperville. The sunniest September was 2004 at 5.3 kWh/m²/day, and the cloudiest was 1993 at 3.3.
Average wind speed in Naperville during September is 2.7 m/s. The windiest September was 1985 at 3.3 m/s, while the calmest was 2025 at 2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 17.6°C | 17.5°C | 18.7°C | 18.8°C | 19.7°C | +2.1°C |
| Avg High | 23.5°C | 23.5°C | 24.7°C | 24.3°C | 25.9°C | +2.4°C |
| Avg Low | 11.6°C | 11.6°C | 12.7°C | 13.4°C | 13.5°C | +1.9°C |
| Avg Rain | 87 mm | 77 mm | 89 mm | 87 mm | 66 mm | -21 mm |
September temperatures in Naperville have risen by about 2.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -0.2°C (1984) to a record high of 35.7°C (2000).
Rainfall in September is about average for rainfall, averaging 82 mm, with a wettest year of 251 mm.
One of the best times to visit Naperville
September is one of the best times to visit Naperville. Expect days averaging 24.3°C and nights around 12.5°C (mean 18.4°C) — warmer than Naperville's yearly average — with higher rainfall (82 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 | 26.9°C | 20.3°C | 13.7°C | 31.6°C | 6.4°C | 35 mm | 66% | 2 m/s | 5 |
| 2024 | 27.5°C | 20.8°C | 14.0°C | 32.7°C | 7.4°C | 41 mm | 61% | 2.4 m/s | 4.8 |
| 2023 | 25.6°C | 19.9°C | 14.2°C | 34.8°C | 9.2°C | 100 mm | 72% | 2.3 m/s | 4 |
| 2022 | 24.8°C | 18.8°C | 12.9°C | 32.4°C | 4.6°C | 83 mm | 72% | 2.5 m/s | 4.7 |
| 2021 | 27.3°C | 20.7°C | 14.1°C | 32.4°C | 7.2°C | 32 mm | 66% | 2.9 m/s | 4.7 |
| 2020 | 23.1°C | 17.5°C | 11.9°C | 30.9°C | 6.1°C | 102 mm | 76% | 3.1 m/s | 4 |
| 2019 | 24.8°C | 20.1°C | 15.3°C | 29.1°C | 10.5°C | 224 mm | 84% | 2.7 m/s | 3.9 |
| 2018 | 24.5°C | 19.3°C | 14.2°C | 31.6°C | 2.6°C | 105 mm | 79% | 2.5 m/s | 4.3 |
| 2017 | 26.7°C | 20.2°C | 13.7°C | 34.5°C | 7.8°C | 12 mm | 66% | 2.5 m/s | 5 |
| 2016 | 25.0°C | 20.2°C | 15.3°C | 32.0°C | 8.8°C | 65 mm | 79% | 3 m/s | 4.4 |
| 2015 | 25.5°C | 20.1°C | 14.8°C | 33.3°C | 7.2°C | 112 mm | 77% | 2.6 m/s | 4.5 |
| 2014 | 22.7°C | 16.9°C | 11.1°C | 29.0°C | 4.1°C | 78 mm | 78% | 2.4 m/s | 4.6 |
| 2013 | 25.2°C | 19.1°C | 13.0°C | 34.9°C | 6.8°C | 58 mm | 73% | 2.7 m/s | 5 |
| 2012 | 23.8°C | 17.7°C | 11.6°C | 32.5°C | 2.7°C | 48 mm | 68% | 2.8 m/s | 4.8 |
| 2011 | 21.6°C | 16.8°C | 11.9°C | 34.3°C | 3.6°C | 99 mm | 74% | 2.9 m/s | 4.2 |
| 2010 | 23.3°C | 17.9°C | 12.6°C | 30.2°C | 8.2°C | 69 mm | 75% | 3.2 m/s | 4.4 |
| 2009 | 23.8°C | 18.4°C | 13.0°C | 28.7°C | 5.6°C | 29 mm | 77% | 2.2 m/s | 4.4 |
| 2008 🌧️ | 23.6°C | 18.4°C | 13.3°C | 34.8°C | 7.5°C | 251 mm | 81% | 2.4 m/s | 3.9 |
| 2007 | 25.1°C | 18.8°C | 12.5°C | 30.8°C | 2.3°C | 37 mm | 74% | 2.9 m/s | 5.2 |
| 2006 | 21.8°C | 16.6°C | 11.3°C | 28.4°C | 4.2°C | 116 mm | 78% | 2.8 m/s | 3.9 |
| 2005 🔥 | 27.9°C | 21.5°C | 15.1°C | 34.3°C | 4.5°C | 65 mm | 65% | 2.9 m/s | 4.4 |
| 2004 | 26.5°C | 19.9°C | 13.4°C | 30.4°C | 8.2°C | 15 mm | 67% | 2.6 m/s | 5.3 |
| 2003 | 24.4°C | 18.0°C | 11.7°C | 31.7°C | 3.2°C | 51 mm | 66% | 2.9 m/s | 4.5 |
| 2002 | 26.9°C | 20.2°C | 13.4°C | 33.8°C | 4.4°C | 65 mm | 67% | 2.4 m/s | 4.8 |
| 2001 | 22.4°C | 16.7°C | 11.0°C | 31.1°C | 2.5°C | 138 mm | 76% | 2.8 m/s | 4.6 |
| 2000 | 24.1°C | 18.1°C | 12.1°C | 35.7°C | 3.5°C | 127 mm | 69% | 3.2 m/s | 4.2 |
| 1999 | 25.0°C | 18.0°C | 10.9°C | 34.1°C | 3.9°C | 89 mm | 62% | 2.9 m/s | 4.9 |
| 1998 | 26.6°C | 20.2°C | 13.8°C | 33.3°C | 9.7°C | 72 mm | 69% | 2.5 m/s | 4.5 |
| 1997 | 24.3°C | 18.2°C | 12.0°C | 31.0°C | 6.9°C | 59 mm | 71% | 2.7 m/s | 4.4 |
| 1996 | 23.0°C | 17.4°C | 11.8°C | 30.1°C | 6.0°C | 68 mm | 73% | 2.5 m/s | 4.2 |
| 1995 | 22.8°C | 16.6°C | 10.4°C | 31.1°C | 1.8°C | 41 mm | 66% | 2.8 m/s | 4.4 |
| 1994 | 24.3°C | 18.5°C | 12.6°C | 31.8°C | 5.5°C | 48 mm | 73% | 2.4 m/s | 4.2 |
| 1993 ❄️ | 19.2°C | 14.4°C | 9.7°C | 24.7°C | 0.5°C | 126 mm | 81% | 2.9 m/s | 3.3 |
| 1992 | 22.0°C | 16.2°C | 10.5°C | 27.8°C | 0.7°C | 148 mm | 77% | 2.9 m/s | 4.1 |
| 1991 | 23.4°C | 17.3°C | 11.2°C | 32.6°C | 0.4°C | 77 mm | 67% | 2.7 m/s | 4.5 |
| 1990 | 24.2°C | 18.4°C | 12.6°C | 32.7°C | 3.5°C | 39 mm | 73% | 2.8 m/s | 4.4 |
| 1989 | 21.5°C | 15.9°C | 10.4°C | 28.3°C | 2.0°C | 76 mm | 76% | 2.5 m/s | 4.5 |
| 1988 | 26.2°C | 19.1°C | 12.0°C | 31.7°C | 5.8°C | 61 mm | 63% | 3 m/s | 4.3 |
| 1987 | 22.4°C | 17.2°C | 11.9°C | 28.0°C | 6.4°C | 58 mm | 79% | 2.4 m/s | 4 |
| 1986 | 24.0°C | 18.7°C | 13.3°C | 28.4°C | 5.7°C | 215 mm | 76% | 2.9 m/s | 3.5 |
| 1985 | 24.0°C | 18.4°C | 12.8°C | 33.5°C | 3.7°C | 63 mm | 70% | 3.3 m/s | 3.9 |
| 1984 | 23.5°C | 17.0°C | 10.4°C | 33.3°C | -0.2°C | 83 mm | 67% | 3 m/s | 3.8 |
| 1983 | 24.4°C | 17.9°C | 11.4°C | 33.2°C | 2.1°C | 104 mm | 68% | 2.9 m/s | — |
| 1982 | 23.6°C | 17.5°C | 11.3°C | 30.0°C | 3.8°C | 41 mm | 73% | 2.8 m/s | — |
| 1981 | 22.1°C | 16.5°C | 10.9°C | 28.0°C | 2.6°C | 82 mm | 76% | 2.9 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 24.3°C with lows near 12.5°C (mean 18.4°C), based on 45 years of NASA POWER data.
September averages 82 mm of rainfall in Naperville, about average for rainfall. The wettest on record was 251 mm in 2008.
The hottest September reached 35.7°C in 2000. The coldest dipped to -0.2°C in 1984.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2.6°C. Daytime highs moved from 23.5°C to 26.4°C and overnight lows from 11.4°C to 13.8°C over the same span.
September is one of the warmer months of the year in Naperville and about average for rainfall, so plan for around 24.3°C daytime highs and 12.5°C at night.
Not quite — September is the 9th coolest month in Naperville, averaging 18.4°C.
For September in Naperville, pack light layers you can adjust through the day, with typical highs of 24.3°C and lows of 12.5°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 72% — moderately humid.
Average wind speed in September is 2.7 m/s. The windiest September on record averaged 3.3 m/s (1985).
The wettest September on record was 2008 with 251 mm. On average, September sees 82 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 Naperville 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.
