September is one of the warmer months of the year in Chatham, with average highs near 19.9°C and lows around 9.1°C (mean 14.5°C). It is about average for rainfall, averaging 70 mm of rainfall and 77% relative humidity across the period.
September is one of the warmer months of the year in Chatham. Across 45 years of records, the warmest September in Chatham was 1999 — when the month averaged 17.7°C — while the coldest was 1986 at 10.6°C. Typical September days reach 19.9°C with nights near 9.1°C. The long-term trend is warming, about 0.8°C per decade.
September is about average for rainfall in Chatham, averaging 70 mm of rainfall. The wettest September on record was 1999 with 173 mm, while the driest was 2025 at 23 mm.
Relative humidity in Chatham during September averages 77%. The most humid September was 1982 at 86%, and the least humid was 2025 at 67%.
September receives about 3.7 kWh/m²/day of solar energy in Chatham. The sunniest Septembers were 2009 and 2025 at 4.3 kWh/m²/day, and the cloudiest was 2010 at 3.1.
Average wind speed in Chatham during September is 0.3 m/s. The windiest Septembers were 2020, 2021 and 2022, among others at 0.4 m/s, while the calmest were 2023, 2024 and 2025, among others at 0.3 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 12.9°C | 14.0°C | 14.6°C | 15.1°C | 16.3°C | +3.4°C |
| Avg High | 18.0°C | 19.4°C | 20.2°C | 20.6°C | 22.0°C | +4°C |
| Avg Low | 7.9°C | 8.6°C | 9.1°C | 9.7°C | 10.5°C | +2.6°C |
| Avg Rain | 81 mm | 75 mm | 70 mm | 69 mm | 48 mm | -32 mm |
September temperatures in Chatham have risen by about 3.1°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -1.1°C (1989) to a record high of 33°C (2010).
Rainfall in September is about average for rainfall, averaging 70 mm, with a wettest year of 173 mm.
Daytime highs and overnight lows have shifted differently — highs rose about 1°C per decade while lows rose 0.6°C per decade, widening the gap between day and night.
One of the best times to visit Chatham
September is one of the best times to visit Chatham. Expect days averaging 19.9°C and nights around 9.1°C (mean 14.5°C) — warmer than Chatham's yearly average — with moderate rainfall (70 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 | 23.2°C | 16.5°C | 9.8°C | 29.2°C | 4.2°C | 23 mm | 67% | 0.3 m/s | 4.3 |
| 2024 | 22.6°C | 17.0°C | 11.4°C | 31.5°C | 7.6°C | 41 mm | 74% | 0.3 m/s | 3.9 |
| 2023 | 23.1°C | 17.3°C | 11.5°C | 30.8°C | 4.3°C | 63 mm | 80% | 0.3 m/s | 3.4 |
| 2022 | 21.5°C | 15.8°C | 10.1°C | 29.8°C | 3.6°C | 39 mm | 71% | 0.4 m/s | 3.9 |
| 2021 | 20.8°C | 16.0°C | 11.1°C | 27.3°C | 6.5°C | 95 mm | 78% | 0.4 m/s | 3.4 |
| 2020 | 21.1°C | 15.0°C | 8.9°C | 28.4°C | 1.1°C | 26 mm | 69% | 0.4 m/s | 4 |
| 2019 | 19.1°C | 13.5°C | 8.0°C | 27.4°C | 2.2°C | 85 mm | 76% | 0.4 m/s | 3.6 |
| 2018 | 21.1°C | 15.1°C | 9.1°C | 30.0°C | 0.7°C | 59 mm | 72% | 0.4 m/s | 4 |
| 2017 | 23.1°C | 17.1°C | 11.1°C | 30.6°C | 3.3°C | 42 mm | 74% | 0.3 m/s | 3.5 |
| 2016 | 20.9°C | 15.4°C | 10.0°C | 28.2°C | 2.7°C | 59 mm | 77% | 0.3 m/s | 3.8 |
| 2015 | 23.3°C | 17.2°C | 11.2°C | 31.1°C | 3.3°C | 90 mm | 73% | 0.3 m/s | 4 |
| 2014 | 20.2°C | 14.6°C | 9.0°C | 29.0°C | 2.4°C | 44 mm | 73% | 0.4 m/s | 4 |
| 2013 | 18.9°C | 14.0°C | 9.0°C | 25.1°C | 3.2°C | 95 mm | 82% | 0.3 m/s | 3.2 |
| 2012 | 20.0°C | 14.8°C | 9.6°C | 27.2°C | 3.3°C | 77 mm | 78% | 0.3 m/s | 3.6 |
| 2011 | 20.2°C | 15.0°C | 9.8°C | 25.6°C | 3.8°C | 37 mm | 82% | 0.3 m/s | 4 |
| 2010 | 19.2°C | 14.6°C | 10.0°C | 33.0°C | 2.6°C | 98 mm | 81% | 0.3 m/s | 3.1 |
| 2009 | 19.9°C | 14.0°C | 8.0°C | 26.0°C | -0.3°C | 52 mm | 75% | 0.3 m/s | 4.3 |
| 2008 | 18.7°C | 13.7°C | 8.7°C | 25.7°C | 0.9°C | 99 mm | 82% | 0.4 m/s | 3.6 |
| 2007 | 19.9°C | 14.3°C | 8.7°C | 29.7°C | 2.7°C | 65 mm | 74% | 0.4 m/s | 4 |
| 2006 | 19.3°C | 13.9°C | 8.5°C | 25.0°C | 4.3°C | 68 mm | 81% | 0.3 m/s | 3.7 |
| 2005 | 20.4°C | 15.3°C | 10.2°C | 27.1°C | 3.4°C | 107 mm | 78% | 0.3 m/s | 3.8 |
| 2004 | 19.8°C | 14.0°C | 8.3°C | 24.9°C | 3.5°C | 54 mm | 74% | 0.3 m/s | 4 |
| 2003 | 22.6°C | 16.7°C | 10.8°C | 30.3°C | 4.3°C | 30 mm | 76% | 0.3 m/s | 4.1 |
| 2002 | 20.8°C | 15.2°C | 9.6°C | 31.2°C | 0.2°C | 96 mm | 77% | 0.3 m/s | 3.4 |
| 2001 | 21.5°C | 15.8°C | 10.1°C | 31.4°C | 3.0°C | 64 mm | 73% | 0.3 m/s | 4.1 |
| 2000 | 19.0°C | 13.4°C | 7.8°C | 26.8°C | 0.5°C | 68 mm | 74% | 0.3 m/s | 3.9 |
| 1999 🔥 🌧️ | 23.0°C | 17.7°C | 12.3°C | 31.0°C | 5.7°C | 173 mm | 79% | 0.3 m/s | 3.5 |
| 1998 | 18.5°C | 13.9°C | 9.2°C | 23.5°C | 3.9°C | 92 mm | 80% | 0.3 m/s | 3.5 |
| 1997 | 19.2°C | 14.0°C | 8.7°C | 26.1°C | 1.8°C | 43 mm | 78% | 0.3 m/s | 3.2 |
| 1996 | 18.8°C | 13.9°C | 9.0°C | 29.7°C | 3.3°C | 78 mm | 77% | 0.4 m/s | 3.5 |
| 1995 | 19.2°C | 12.8°C | 6.4°C | 25.1°C | -0.1°C | 55 mm | 70% | 0.4 m/s | 4.2 |
| 1994 | 18.8°C | 13.5°C | 8.1°C | 24.8°C | 3.6°C | 58 mm | 76% | 0.3 m/s | 3.8 |
| 1993 | 19.6°C | 14.1°C | 8.6°C | 28.5°C | 2.4°C | 66 mm | 74% | 0.4 m/s | 3.8 |
| 1992 | 21.0°C | 15.0°C | 9.0°C | 26.7°C | 1.1°C | 27 mm | 74% | 0.3 m/s | 3.7 |
| 1991 | 17.4°C | 12.3°C | 7.2°C | 25.9°C | -0.2°C | 96 mm | 79% | 0.3 m/s | 3.5 |
| 1990 | 18.2°C | 12.9°C | 7.6°C | 24.9°C | 1.9°C | 59 mm | 80% | 0.4 m/s | 3.5 |
| 1989 | 18.6°C | 13.5°C | 8.3°C | 28.5°C | -1.1°C | 73 mm | 81% | 0.3 m/s | 3.8 |
| 1988 | 17.4°C | 12.3°C | 7.3°C | 23.9°C | 2.8°C | 58 mm | 79% | 0.4 m/s | 3.6 |
| 1987 | 17.4°C | 13.1°C | 8.8°C | 27.5°C | -0.4°C | 133 mm | 82% | 0.4 m/s | 3.4 |
| 1986 ❄️ | 15.9°C | 10.6°C | 5.3°C | 22.6°C | 0.7°C | 91 mm | 80% | 0.3 m/s | 3.7 |
| 1985 | 20.4°C | 14.6°C | 8.8°C | 28.1°C | 4.2°C | 47 mm | 74% | 0.3 m/s | 3.8 |
| 1984 | 17.4°C | 12.1°C | 6.8°C | 24.6°C | 1.5°C | 44 mm | 78% | 0.4 m/s | 4.1 |
| 1983 | 20.1°C | 14.7°C | 9.4°C | 29.9°C | 3.7°C | 73 mm | 80% | 0.3 m/s | — |
| 1982 | 17.5°C | 13.0°C | 8.5°C | 25.5°C | 1.7°C | 101 mm | 86% | 0.3 m/s | — |
| 1981 | 17.0°C | 12.6°C | 8.2°C | 23.3°C | 2.5°C | 105 mm | 84% | 0.4 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 19.9°C with lows near 9.1°C (mean 14.5°C), based on 45 years of NASA POWER data.
September averages 70 mm of rainfall in Chatham, about average for rainfall. The wettest on record was 173 mm in 1999.
The hottest September reached 33°C in 2010. The coldest dipped to -1.1°C in 1989.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 3.1°C. Daytime highs moved from 18.5°C to 22.2°C and overnight lows from 8.3°C to 10.8°C over the same span.
September is one of the warmer months of the year in Chatham and about average for rainfall, so plan for around 19.9°C daytime highs and 9.1°C at night.
Not quite — September is the 9th coolest month in Chatham, averaging 14.5°C.
For September in Chatham, pack light layers you can adjust through the day, with typical highs of 19.9°C and lows of 9.1°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 77% — quite humid.
Average wind speed in September is 0.3 m/s. The windiest September on record averaged 0.4 m/s (1981).
The wettest September on record was 1999 with 173 mm. On average, September sees 70 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 Chatham 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.
