September is one of the warmer months of the year in Norristown, with average highs near 25.8°C and lows around 14°C (mean 19.9°C). It is a relatively wet time of year, averaging 110 mm of rainfall and 72% relative humidity across the period.
September is one of the warmer months of the year in Norristown. Across 45 years of records, the warmest September in Norristown was 2005 — when the month averaged 22.5°C — while the coldest was 1984 at 17.4°C. Typical September days reach 25.8°C with nights near 14°C. The long-term trend is warming, about 0.6°C per decade.
September is a relatively wet time of year in Norristown, averaging 110 mm of rainfall. The wettest September on record was 1999 with 287 mm, while the driest was 2019 at 19 mm.
Relative humidity in Norristown during September averages 72%. The most humid September was 2011 at 88%, and the least humid was 1983 at 59%.
September receives about 4.2 kWh/m²/day of solar energy in Norristown. The sunniest September was 2007 at 5 kWh/m²/day, and the cloudiest was 2018 at 3.1.
Average wind speed in Norristown during September is 0.4 m/s. The windiest Septembers were 1999 and 2016 at 0.5 m/s, while the calmest were 2023, 2024 and 2025, among others at 0.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 19.1°C | 19.3°C | 19.8°C | 20.8°C | 20.7°C | +1.6°C |
| Avg High | 25.2°C | 25.1°C | 25.7°C | 26.7°C | 26.4°C | +1.2°C |
| Avg Low | 12.9°C | 13.4°C | 14.0°C | 14.9°C | 15.0°C | +2.1°C |
| Avg Rain | 97 mm | 118 mm | 116 mm | 113 mm | 104 mm | +6 mm |
September temperatures in Norristown have risen by about 1.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 3°C (1989) to a record high of 37.2°C (2023).
Rainfall in September is a relatively wet time of year, averaging 110 mm, with a wettest year of 287 mm.
One of the best times to visit Norristown
September is one of the best times to visit Norristown. Expect days averaging 25.8°C and nights around 14°C (mean 19.9°C) — warmer than Norristown's yearly average — with higher rainfall (110 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 | 21.7°C | 15.4°C | 32.1°C | 11.2°C | 67 mm | 68% | 0.4 m/s | 4.4 |
| 2024 | 26.8°C | 21.0°C | 15.2°C | 31.0°C | 9.1°C | 29 mm | 72% | 0.4 m/s | 4.1 |
| 2023 | 26.7°C | 21.1°C | 15.4°C | 37.2°C | 10.3°C | 155 mm | 74% | 0.4 m/s | 4.1 |
| 2022 | 26.2°C | 20.4°C | 14.6°C | 32.4°C | 6.9°C | 93 mm | 70% | 0.4 m/s | 4.3 |
| 2021 | 25.3°C | 20.4°C | 15.4°C | 29.9°C | 9.8°C | 189 mm | 81% | 0.4 m/s | 4.2 |
| 2020 | 25.5°C | 19.7°C | 13.8°C | 30.3°C | 5.1°C | 89 mm | 73% | 0.4 m/s | 4.1 |
| 2019 | 29.0°C | 22.3°C | 15.6°C | 34.6°C | 8.8°C | 19 mm | 65% | 0.4 m/s | 4.3 |
| 2018 | 25.8°C | 21.4°C | 17.0°C | 34.9°C | 10.3°C | 199 mm | 86% | 0.4 m/s | 3.1 |
| 2017 | 26.4°C | 20.6°C | 14.8°C | 33.9°C | 8.6°C | 56 mm | 72% | 0.4 m/s | 4.4 |
| 2016 | 28.2°C | 21.9°C | 15.7°C | 35.2°C | 9.3°C | 109 mm | 65% | 0.5 m/s | 4.5 |
| 2015 | 28.3°C | 21.9°C | 15.5°C | 35.1°C | 10.9°C | 103 mm | 68% | 0.4 m/s | 4.5 |
| 2014 | 26.4°C | 20.3°C | 14.2°C | 32.9°C | 7.5°C | 54 mm | 69% | 0.4 m/s | 4.4 |
| 2013 | 25.2°C | 18.5°C | 11.9°C | 34.3°C | 5.3°C | 49 mm | 70% | 0.4 m/s | 4.9 |
| 2012 | 25.0°C | 19.4°C | 13.9°C | 34.0°C | 7.3°C | 129 mm | 76% | 0.4 m/s | 4.2 |
| 2011 | 24.6°C | 20.1°C | 15.6°C | 28.2°C | 6.3°C | 259 mm | 88% | 0.4 m/s | 3.2 |
| 2010 | 27.9°C | 21.5°C | 15.1°C | 36.3°C | 8.6°C | 150 mm | 63% | 0.4 m/s | 4.5 |
| 2009 | 22.8°C | 18.0°C | 13.2°C | 27.5°C | 6.9°C | 110 mm | 81% | 0.4 m/s | 4 |
| 2008 | 26.1°C | 20.3°C | 14.6°C | 34.5°C | 7.7°C | 151 mm | 74% | 0.4 m/s | 4.3 |
| 2007 | 28.0°C | 21.4°C | 14.9°C | 33.1°C | 7.3°C | 21 mm | 67% | 0.4 m/s | 5 |
| 2006 | 22.9°C | 18.0°C | 13.1°C | 27.8°C | 6.5°C | 146 mm | 82% | 0.4 m/s | 3.6 |
| 2005 🔥 | 29.4°C | 22.5°C | 15.7°C | 34.4°C | 7.0°C | 24 mm | 61% | 0.4 m/s | 4.9 |
| 2004 | 25.8°C | 20.3°C | 14.8°C | 29.8°C | 7.6°C | 192 mm | 80% | 0.4 m/s | 4 |
| 2003 | 24.3°C | 19.4°C | 14.5°C | 28.3°C | 6.6°C | 205 mm | 83% | 0.4 m/s | 3.7 |
| 2002 | 27.7°C | 21.1°C | 14.6°C | 34.6°C | 9.8°C | 96 mm | 66% | 0.4 m/s | 4.5 |
| 2001 | 25.6°C | 19.0°C | 12.3°C | 30.9°C | 5.6°C | 81 mm | 66% | 0.4 m/s | 4.6 |
| 2000 | 23.9°C | 17.9°C | 12.0°C | 31.3°C | 3.7°C | 135 mm | 75% | 0.4 m/s | 4.1 |
| 1999 🌧️ | 24.6°C | 19.3°C | 13.9°C | 31.4°C | 6.2°C | 287 mm | 78% | 0.5 m/s | 4 |
| 1998 | 28.2°C | 21.4°C | 14.7°C | 33.3°C | 5.5°C | 50 mm | 64% | 0.4 m/s | 4.3 |
| 1997 | 24.8°C | 18.8°C | 12.8°C | 31.5°C | 4.8°C | 67 mm | 69% | 0.4 m/s | 4.2 |
| 1996 | 24.6°C | 19.4°C | 14.2°C | 31.3°C | 7.6°C | 140 mm | 79% | 0.4 m/s | 3.7 |
| 1995 | 25.8°C | 19.4°C | 12.9°C | 33.2°C | 6.0°C | 100 mm | 64% | 0.4 m/s | 4.3 |
| 1994 | 23.9°C | 18.1°C | 12.3°C | 29.7°C | 7.1°C | 77 mm | 73% | 0.4 m/s | 4.2 |
| 1993 | 24.5°C | 19.3°C | 14.0°C | 32.9°C | 3.2°C | 181 mm | 76% | 0.4 m/s | 3.3 |
| 1992 | 24.7°C | 19.0°C | 13.3°C | 30.5°C | 3.8°C | 112 mm | 73% | 0.4 m/s | 3.8 |
| 1991 | 25.3°C | 19.2°C | 13.1°C | 34.2°C | 3.4°C | 105 mm | 67% | 0.4 m/s | 4.3 |
| 1990 | 24.8°C | 18.7°C | 12.6°C | 32.5°C | 4.3°C | 58 mm | 71% | 0.4 m/s | 4.2 |
| 1989 | 24.6°C | 19.2°C | 13.8°C | 33.5°C | 3.0°C | 143 mm | 77% | 0.4 m/s | 3.9 |
| 1988 | 24.3°C | 18.0°C | 11.7°C | 29.4°C | 6.5°C | 73 mm | 72% | 0.4 m/s | 4.4 |
| 1987 | 24.1°C | 18.9°C | 13.7°C | 28.7°C | 6.4°C | 170 mm | 81% | 0.4 m/s | 3.9 |
| 1986 | 25.4°C | 19.3°C | 13.3°C | 31.6°C | 5.1°C | 56 mm | 71% | 0.4 m/s | 3.9 |
| 1985 | 26.6°C | 20.3°C | 14.0°C | 33.8°C | 6.9°C | 158 mm | 67% | 0.4 m/s | 4.5 |
| 1984 ❄️ | 23.9°C | 17.4°C | 10.9°C | 30.9°C | 4.5°C | 54 mm | 71% | 0.4 m/s | 4.5 |
| 1983 | 27.5°C | 20.4°C | 13.3°C | 36.4°C | 4.6°C | 63 mm | 59% | 0.4 m/s | — |
| 1982 | 25.8°C | 19.4°C | 13.0°C | 31.6°C | 8.3°C | 68 mm | 69% | 0.4 m/s | — |
| 1981 | 24.8°C | 18.8°C | 12.7°C | 32.4°C | 5.0°C | 89 mm | 68% | 0.4 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 25.8°C with lows near 14°C (mean 19.9°C), based on 45 years of NASA POWER data.
September averages 110 mm of rainfall in Norristown, a relatively wet time of year. The wettest on record was 287 mm in 1999.
The hottest September reached 37.2°C in 2023. The coldest dipped to 3°C in 1989.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.6°C. Daytime highs moved from 25.7°C to 26.6°C and overnight lows from 12.8°C to 15.2°C over the same span.
September is one of the warmer months of the year in Norristown and a relatively wet time of year, so plan for around 25.8°C daytime highs and 14°C at night.
Not quite — September is the 9th coolest month in Norristown, averaging 19.9°C.
For September in Norristown, pack light layers you can adjust through the day, with typical highs of 25.8°C and lows of 14°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 72% — moderately humid.
Average wind speed in September is 0.4 m/s. The windiest September on record averaged 0.5 m/s (1999).
The wettest September on record was 1999 with 287 mm. On average, September sees 110 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 Norristown 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.
