September is one of the cooler months of the year in Hamilton, with average highs near 15°C and lows around 8.7°C (mean 11.9°C). It is about average for rainfall, averaging 99 mm of rainfall and 83% relative humidity across the period.
September is one of the cooler months of the year in Hamilton. Across 45 years of records, the warmest September in Hamilton was 2005 — when the month averaged 12.9°C — while the coldest was 1992 at 9.8°C. Typical September days reach 15°C with nights near 8.7°C. The long-term trend is warming, about 0.2°C per decade.
September is about average for rainfall in Hamilton, averaging 99 mm of rainfall. The wettest September on record was 2023 with 166 mm, while the driest was 2006 at 40 mm.
Relative humidity in Hamilton during September averages 83%. The most humid September was 1988 at 87%, and the least humid was 2012 at 81%.
September receives about 3.7 kWh/m²/day of solar energy in Hamilton. The sunniest Septembers were 1990, 2018 and 2020, among others at 4.1 kWh/m²/day, and the cloudiest were 2010 and 2016 at 3.2.
Average wind speed in Hamilton during September is 4.3 m/s. The windiest September was 1981 at 5.6 m/s, while the calmest was 2007 at 3.3 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 11.9°C | 11.2°C | 12.1°C | 11.8°C | 12.1°C | +0.2°C |
| Avg High | 15.0°C | 14.3°C | 15.5°C | 14.9°C | 15.2°C | +0.2°C |
| Avg Low | 8.7°C | 8.2°C | 8.7°C | 8.8°C | 9.1°C | +0.4°C |
| Avg Rain | 88 mm | 105 mm | 79 mm | 107 mm | 130 mm | +42 mm |
September temperatures in Hamilton have risen by about 0.5°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 1.4°C (1989) to a record high of 21.4°C (2023).
Rainfall in September is about average for rainfall, averaging 99 mm, with a wettest year of 166 mm.
A quieter season to visit Hamilton
If your dates are flexible, the more temperate months of February and January tend to be the most comfortable for visiting Hamilton. That said, September — with days averaging 15°C and nights around 8.7°C (mean 11.9°C) and higher rainfall (99 mm) — can still be rewarding for travellers who don't mind the cooler conditions, and often means fewer crowds.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 15.1°C | 12.3°C | 9.6°C | 18.3°C | 4.3°C | 132 mm | 83% | 5 m/s | 3.6 |
| 2024 | 15.1°C | 12.0°C | 8.8°C | 18.5°C | 4.5°C | 95 mm | 84% | 4.5 m/s | 4 |
| 2023 🌧️ | 16.0°C | 12.8°C | 9.7°C | 21.4°C | 5.7°C | 166 mm | 85% | 4.6 m/s | 3.9 |
| 2022 | 15.4°C | 12.4°C | 9.4°C | 20.4°C | 4.6°C | 156 mm | 81% | 3.5 m/s | 3.6 |
| 2021 | 14.8°C | 11.5°C | 8.3°C | 17.7°C | 3.8°C | 145 mm | 82% | 4.4 m/s | 3.7 |
| 2020 | 14.9°C | 11.7°C | 8.5°C | 19.1°C | 2.3°C | 83 mm | 81% | 4.7 m/s | 4.1 |
| 2019 | 15.0°C | 11.9°C | 8.7°C | 18.4°C | 5.7°C | 111 mm | 83% | 4.7 m/s | 3.9 |
| 2018 | 15.3°C | 12.0°C | 8.7°C | 20.1°C | 5.8°C | 42 mm | 82% | 3.9 m/s | 4.1 |
| 2017 | 14.8°C | 12.0°C | 9.3°C | 18.4°C | 5.2°C | 146 mm | 85% | 4.4 m/s | 3.7 |
| 2016 | 15.4°C | 12.4°C | 9.4°C | 18.2°C | 4.2°C | 137 mm | 86% | 4.2 m/s | 3.2 |
| 2015 | 14.1°C | 11.1°C | 8.0°C | 17.2°C | 5.7°C | 100 mm | 82% | 3.9 m/s | 4 |
| 2014 | 15.4°C | 12.1°C | 8.8°C | 18.1°C | 3.5°C | 125 mm | 84% | 4.3 m/s | 3.6 |
| 2013 | 15.1°C | 12.1°C | 9.1°C | 17.3°C | 3.1°C | 109 mm | 83% | 4.8 m/s | 3.6 |
| 2012 | 15.0°C | 11.8°C | 8.7°C | 19.9°C | 3.0°C | 92 mm | 81% | 4.7 m/s | 3.7 |
| 2011 | 14.2°C | 11.0°C | 7.9°C | 17.7°C | 4.5°C | 63 mm | 81% | 4 m/s | 4 |
| 2010 | 14.6°C | 12.0°C | 9.4°C | 18.0°C | 6.0°C | 144 mm | 85% | 5.4 m/s | 3.2 |
| 2009 | 16.0°C | 12.2°C | 8.3°C | 17.8°C | 1.4°C | 94 mm | 84% | 3.4 m/s | 3.8 |
| 2008 | 15.3°C | 12.0°C | 8.8°C | 17.5°C | 6.2°C | 61 mm | 84% | 4 m/s | 3.9 |
| 2007 | 15.5°C | 11.9°C | 8.3°C | 18.4°C | 3.4°C | 49 mm | 82% | 3.3 m/s | 3.7 |
| 2006 | 15.6°C | 12.4°C | 9.2°C | 19.1°C | 5.6°C | 40 mm | 84% | 3.4 m/s | 3.7 |
| 2005 🔥 | 16.5°C | 12.9°C | 9.4°C | 19.7°C | 5.5°C | 84 mm | 83% | 3.9 m/s | 3.7 |
| 2004 | 14.1°C | 10.9°C | 7.6°C | 16.8°C | 3.0°C | 84 mm | 82% | 4.7 m/s | 3.6 |
| 2003 | 15.3°C | 12.3°C | 9.3°C | 19.3°C | 5.8°C | 162 mm | 85% | 5 m/s | 3.4 |
| 2002 | 14.9°C | 11.9°C | 8.9°C | 17.7°C | 4.1°C | 94 mm | 82% | 4.7 m/s | 3.6 |
| 2001 | 16.1°C | 12.4°C | 8.6°C | 18.3°C | 4.2°C | 41 mm | 81% | 3.5 m/s | 3.7 |
| 2000 | 15.2°C | 11.9°C | 8.6°C | 18.3°C | 3.6°C | 82 mm | 82% | 4.2 m/s | 3.7 |
| 1999 | 15.6°C | 12.0°C | 8.4°C | 18.2°C | 3.7°C | 66 mm | 83% | 3.6 m/s | 4 |
| 1998 | 15.5°C | 12.4°C | 9.2°C | 18.7°C | 5.5°C | 61 mm | 82% | 4.2 m/s | 3.7 |
| 1997 | 14.2°C | 11.1°C | 8.0°C | 16.5°C | 2.6°C | 134 mm | 83% | 4.5 m/s | 3.6 |
| 1996 | 15.7°C | 12.2°C | 8.8°C | 19.4°C | 4.6°C | 130 mm | 86% | 4 m/s | 3.6 |
| 1995 | 14.7°C | 11.7°C | 8.8°C | 19.0°C | 2.7°C | 110 mm | 85% | 3.8 m/s | 3.7 |
| 1994 | 13.2°C | 10.5°C | 7.9°C | 16.2°C | 4.7°C | 145 mm | 85% | 5 m/s | 3.6 |
| 1993 | 13.0°C | 10.0°C | 7.0°C | 16.7°C | 2.5°C | 61 mm | 81% | 4.4 m/s | 3.8 |
| 1992 ❄️ | 12.7°C | 9.8°C | 7.0°C | 15.2°C | 2.1°C | 144 mm | 86% | 4 m/s | 3.8 |
| 1991 | 14.3°C | 11.7°C | 9.1°C | 17.1°C | 4.9°C | 112 mm | 85% | 4.2 m/s | 3.8 |
| 1990 | 13.9°C | 10.7°C | 7.5°C | 16.0°C | 3.2°C | 86 mm | 81% | 3.5 m/s | 4.1 |
| 1989 | 16.6°C | 12.7°C | 8.8°C | 20.1°C | 1.4°C | 59 mm | 81% | 3.6 m/s | 3.7 |
| 1988 | 15.3°C | 12.5°C | 9.7°C | 19.2°C | 3.6°C | 95 mm | 87% | 4.4 m/s | 3.4 |
| 1987 | 14.4°C | 11.7°C | 9.1°C | 17.5°C | 5.7°C | 104 mm | 83% | 5.2 m/s | 3.7 |
| 1986 | 14.3°C | 11.3°C | 8.4°C | 17.4°C | 3.4°C | 91 mm | 84% | 4.4 m/s | 3.8 |
| 1985 | 15.1°C | 12.0°C | 8.9°C | 18.0°C | 4.5°C | 82 mm | 81% | 5.1 m/s | 4.1 |
| 1984 | 15.2°C | 11.5°C | 7.7°C | 17.7°C | 4.1°C | 83 mm | 82% | 3.7 m/s | 3.9 |
| 1983 | 15.2°C | 12.1°C | 9.0°C | 17.9°C | 4.4°C | 112 mm | 84% | 4.7 m/s | — |
| 1982 | 15.2°C | 11.5°C | 7.9°C | 17.7°C | 3.8°C | 73 mm | 81% | 3.4 m/s | — |
| 1981 | 14.0°C | 11.5°C | 9.0°C | 16.7°C | 5.4°C | 94 mm | 83% | 5.6 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 15°C with lows near 8.7°C (mean 11.9°C), based on 45 years of NASA POWER data.
September averages 99 mm of rainfall in Hamilton, about average for rainfall. The wettest on record was 166 mm in 2023.
The hottest September reached 21.4°C in 2023. The coldest dipped to 1.4°C in 1989.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 0.5°C. Daytime highs moved from 14.9°C to 15.3°C and overnight lows from 8.5°C to 9.2°C over the same span.
September is one of the cooler months of the year in Hamilton and about average for rainfall, so plan for around 15°C daytime highs and 8.7°C at night.
Not quite — September is the 4th coolest month in Hamilton, averaging 11.9°C.
For September in Hamilton, pack light layers you can adjust through the day, with typical highs of 15°C and lows of 8.7°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 83% — quite humid.
Average wind speed in September is 4.3 m/s. The windiest September on record averaged 5.6 m/s (1981).
The wettest September on record was 2023 with 166 mm. On average, September sees 99 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 Hamilton 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.
