September is one of the warmer months of the year in Waterbury, with average highs near 24.1°C and lows around 12.4°C (mean 18.3°C). It is about average for rainfall, averaging 107 mm of rainfall and 74% relative humidity across the period.
September is one of the warmer months of the year in Waterbury. Across 45 years of records, the warmest September in Waterbury was 2015 — when the month averaged 21.2°C — while the coldest was 1984 at 15.7°C. Typical September days reach 24.1°C with nights near 12.4°C. The long-term trend is warming, about 0.6°C per decade.
September is about average for rainfall in Waterbury, averaging 107 mm of rainfall. The wettest September on record was 2023 with 255 mm, while the driest was 2024 at 26 mm.
Relative humidity in Waterbury during September averages 74%. The most humid September was 2011 at 86%, and the least humid was 1983 at 62%.
September receives about 4.3 kWh/m²/day of solar energy in Waterbury. The sunniest Septembers were 1984 and 2007 at 4.9 kWh/m²/day, and the cloudiest was 2018 at 3.3.
Average wind speed in Waterbury during September is 0.2 m/s. The windiest Septembers were 2023, 2024 and 2025, among others at 0.2 m/s, while the calmest were 1984, 1987 and 1998 at 0.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 17.4°C | 17.5°C | 18.4°C | 19.3°C | 19.0°C | +1.6°C |
| Avg High | 23.5°C | 23.3°C | 24.3°C | 25.2°C | 24.7°C | +1.2°C |
| Avg Low | 11.3°C | 11.8°C | 12.6°C | 13.5°C | 13.3°C | +2°C |
| Avg Rain | 84 mm | 114 mm | 115 mm | 100 mm | 130 mm | +47 mm |
September temperatures in Waterbury have risen by about 1.5°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 0.4°C (1991) to a record high of 35.2°C (2015).
Rainfall in September is about average for rainfall, averaging 107 mm, with a wettest year of 255 mm.
One of the best times to visit Waterbury
September is one of the best times to visit Waterbury. Expect days averaging 24.1°C and nights around 12.4°C (mean 18.3°C) — warmer than Waterbury's yearly average — with higher rainfall (107 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 | 26.1°C | 19.9°C | 13.7°C | 29.7°C | 9.0°C | 75 mm | 72% | 0.2 m/s | 4.5 |
| 2024 | 25.0°C | 18.9°C | 12.7°C | 30.1°C | 8.9°C | 26 mm | 73% | 0.2 m/s | 4.4 |
| 2023 🌧️ | 24.2°C | 19.1°C | 14.1°C | 34.9°C | 6.1°C | 255 mm | 81% | 0.2 m/s | 3.9 |
| 2022 | 24.0°C | 18.5°C | 13.0°C | 31.1°C | 5.6°C | 150 mm | 76% | 0.2 m/s | 4.3 |
| 2021 | 23.9°C | 18.9°C | 13.9°C | 28.2°C | 8.4°C | 208 mm | 81% | 0.2 m/s | 4.3 |
| 2020 | 24.7°C | 18.6°C | 12.5°C | 31.0°C | 3.2°C | 68 mm | 71% | 0.2 m/s | 4.4 |
| 2019 | 25.4°C | 19.0°C | 12.7°C | 31.0°C | 4.9°C | 43 mm | 70% | 0.2 m/s | 4.5 |
| 2018 | 24.5°C | 19.8°C | 15.1°C | 34.3°C | 7.1°C | 201 mm | 83% | 0.2 m/s | 3.3 |
| 2017 | 25.9°C | 20.0°C | 14.1°C | 34.3°C | 7.2°C | 57 mm | 72% | 0.2 m/s | 4.4 |
| 2016 | 26.4°C | 20.3°C | 14.3°C | 32.7°C | 5.0°C | 50 mm | 68% | 0.2 m/s | 4.4 |
| 2015 🔥 | 28.0°C | 21.2°C | 14.4°C | 35.2°C | 6.7°C | 96 mm | 70% | 0.2 m/s | 4.7 |
| 2014 | 25.3°C | 19.0°C | 12.6°C | 32.4°C | 6.3°C | 34 mm | 69% | 0.2 m/s | 4.5 |
| 2013 | 23.6°C | 17.2°C | 10.8°C | 34.0°C | 4.7°C | 61 mm | 72% | 0.2 m/s | 4.6 |
| 2012 | 23.8°C | 18.1°C | 12.4°C | 31.8°C | 6.2°C | 135 mm | 76% | 0.2 m/s | 4.2 |
| 2011 | 23.5°C | 19.0°C | 14.4°C | 27.4°C | 5.6°C | 227 mm | 86% | 0.2 m/s | 3.8 |
| 2010 | 25.7°C | 19.8°C | 14.0°C | 34.9°C | 6.8°C | 94 mm | 70% | 0.2 m/s | 4.3 |
| 2009 | 23.0°C | 17.2°C | 11.5°C | 28.1°C | 5.3°C | 52 mm | 75% | 0.2 m/s | 4.3 |
| 2008 | 23.5°C | 18.1°C | 12.6°C | 32.8°C | 5.6°C | 214 mm | 80% | 0.2 m/s | 4.4 |
| 2007 | 26.4°C | 19.8°C | 13.3°C | 31.9°C | 5.8°C | 43 mm | 69% | 0.2 m/s | 4.9 |
| 2006 | 21.8°C | 16.8°C | 11.8°C | 26.7°C | 5.0°C | 85 mm | 81% | 0.2 m/s | 3.9 |
| 2005 | 27.8°C | 21.1°C | 14.3°C | 34.2°C | 7.5°C | 50 mm | 65% | 0.2 m/s | 4.8 |
| 2004 | 24.1°C | 18.6°C | 13.1°C | 30.2°C | 6.6°C | 214 mm | 81% | 0.2 m/s | 4.1 |
| 2003 | 23.2°C | 18.2°C | 13.2°C | 27.2°C | 7.5°C | 186 mm | 82% | 0.2 m/s | 3.8 |
| 2002 | 25.5°C | 19.5°C | 13.4°C | 35.1°C | 7.2°C | 107 mm | 72% | 0.2 m/s | 4.5 |
| 2001 | 24.3°C | 18.0°C | 11.7°C | 30.7°C | 6.6°C | 103 mm | 71% | 0.2 m/s | 4.6 |
| 2000 | 23.0°C | 17.0°C | 11.0°C | 31.2°C | 0.6°C | 100 mm | 74% | 0.2 m/s | 4.2 |
| 1999 | 24.0°C | 18.6°C | 13.2°C | 33.2°C | 6.8°C | 251 mm | 79% | 0.2 m/s | 4.1 |
| 1998 | 25.8°C | 19.1°C | 12.4°C | 31.7°C | 3.9°C | 70 mm | 69% | 0.1 m/s | 4.4 |
| 1997 | 23.5°C | 17.4°C | 11.4°C | 29.0°C | 3.8°C | 41 mm | 71% | 0.2 m/s | 4.5 |
| 1996 | 23.0°C | 18.1°C | 13.2°C | 32.0°C | 6.2°C | 153 mm | 78% | 0.2 m/s | 3.6 |
| 1995 | 23.6°C | 17.3°C | 11.0°C | 30.3°C | 4.9°C | 89 mm | 66% | 0.2 m/s | 4.3 |
| 1994 | 22.2°C | 16.7°C | 11.2°C | 28.1°C | 7.4°C | 109 mm | 74% | 0.2 m/s | 4.3 |
| 1993 | 22.9°C | 17.5°C | 12.2°C | 31.1°C | 3.0°C | 143 mm | 76% | 0.2 m/s | 3.4 |
| 1992 | 22.4°C | 16.9°C | 11.3°C | 28.3°C | 3.0°C | 91 mm | 76% | 0.2 m/s | 4 |
| 1991 | 22.4°C | 16.6°C | 10.8°C | 32.5°C | 0.4°C | 136 mm | 72% | 0.2 m/s | 4.3 |
| 1990 | 22.8°C | 16.9°C | 11.0°C | 29.7°C | 3.0°C | 58 mm | 75% | 0.2 m/s | 4.4 |
| 1989 | 23.0°C | 17.3°C | 11.6°C | 33.2°C | 1.0°C | 121 mm | 78% | 0.2 m/s | 4.1 |
| 1988 | 23.2°C | 16.8°C | 10.3°C | 28.9°C | 4.4°C | 64 mm | 70% | 0.2 m/s | 4.7 |
| 1987 | 21.9°C | 16.9°C | 11.9°C | 26.8°C | 4.7°C | 160 mm | 81% | 0.1 m/s | 3.8 |
| 1986 | 23.5°C | 17.4°C | 11.3°C | 30.1°C | 3.9°C | 29 mm | 70% | 0.2 m/s | 4 |
| 1985 | 23.9°C | 17.8°C | 11.7°C | 30.2°C | 5.0°C | 116 mm | 74% | 0.2 m/s | 4.4 |
| 1984 ❄️ | 21.9°C | 15.7°C | 9.5°C | 28.6°C | 3.6°C | 45 mm | 70% | 0.1 m/s | 4.9 |
| 1983 | 26.7°C | 19.5°C | 12.4°C | 34.6°C | 4.8°C | 60 mm | 62% | 0.2 m/s | — |
| 1982 | 24.5°C | 18.0°C | 11.6°C | 31.4°C | 8.1°C | 56 mm | 70% | 0.2 m/s | — |
| 1981 | 22.9°C | 17.0°C | 11.1°C | 30.7°C | 2.8°C | 102 mm | 69% | 0.2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 24.1°C with lows near 12.4°C (mean 18.3°C), based on 45 years of NASA POWER data.
September averages 107 mm of rainfall in Waterbury, about average for rainfall. The wettest on record was 255 mm in 2023.
The hottest September reached 35.2°C in 2015. The coldest dipped to 0.4°C in 1991.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.5°C. Daytime highs moved from 24°C to 24.6°C and overnight lows from 11.3°C to 13.5°C over the same span.
September is one of the warmer months of the year in Waterbury and about average for rainfall, so plan for around 24.1°C daytime highs and 12.4°C at night.
Not quite — September is the 9th coolest month in Waterbury, averaging 18.3°C.
For September in Waterbury, pack light layers you can adjust through the day, with typical highs of 24.1°C and lows of 12.4°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 74% — moderately humid.
Average wind speed in September is 0.2 m/s. The windiest September on record averaged 0.2 m/s (1981).
The wettest September on record was 2023 with 255 mm. On average, September sees 107 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 Waterbury 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.
