September is one of the cooler months of the year in Atherton, with average highs near 25.5°C and lows around 15.5°C (mean 20.5°C). It is one of the drier months, averaging 42 mm of rainfall and 76% relative humidity across the period.
September is one of the cooler months of the year in Atherton. Across 45 years of records, the warmest Septembers in Atherton were 2016 and 2022 — when the month averaged 23.4°C — while the coldest was 1990 at 17.6°C. Typical September days reach 25.5°C with nights near 15.5°C. The long-term trend is warming, about 0.5°C per decade.
September is one of the drier months in Atherton, averaging 42 mm of rainfall. The wettest September on record was 1998 with 182 mm, while the driest was 1991 at 0 mm.
Relative humidity in Atherton during September averages 76%. The most humid September was 1998 at 89%, and the least humid was 2019 at 63%.
September receives about 6 kWh/m²/day of solar energy in Atherton. The sunniest September was 2019 at 6.7 kWh/m²/day, and the cloudiest was 2010 at 5.
Average wind speed in Atherton during September is 1.2 m/s. The windiest September was 2020 at 1.6 m/s, while the calmest was 1984 at 0.9 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 19.9°C | 19.9°C | 20.3°C | 21.0°C | 21.8°C | +1.9°C |
| Avg High | 24.8°C | 24.7°C | 25.5°C | 26.2°C | 26.8°C | +2°C |
| Avg Low | 15.1°C | 15.1°C | 15.3°C | 15.8°C | 16.9°C | +1.8°C |
| Avg Rain | 56 mm | 58 mm | 34 mm | 30 mm | 32 mm | -23 mm |
September temperatures in Atherton have risen by about 2°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 7.3°C (2006) to a record high of 34.3°C (1996).
Rainfall in September is one of the drier months, averaging 42 mm, with a wettest year of 182 mm.
One of the best times to visit Atherton
September is one of the best times to visit Atherton. Expect days averaging 25.5°C and nights around 15.5°C (mean 20.5°C) — cooler than Atherton's yearly average — with moderate rainfall (42 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 | 21.9°C | 16.9°C | 30.5°C | 14.5°C | 94 mm | 76% | 1.4 m/s | 5.3 |
| 2024 | 27.2°C | 22.2°C | 17.2°C | 32.7°C | 15.0°C | 15 mm | 74% | 1.4 m/s | 5.4 |
| 2023 | 25.6°C | 20.9°C | 16.1°C | 30.4°C | 13.2°C | 26 mm | 74% | 1.5 m/s | 5.7 |
| 2022 | 28.8°C | 23.4°C | 18.0°C | 33.6°C | 13.3°C | 15 mm | 74% | 1.2 m/s | 5.9 |
| 2021 | 25.8°C | 21.0°C | 16.2°C | 30.5°C | 11.7°C | 14 mm | 73% | 1.5 m/s | 5.5 |
| 2020 | 26.4°C | 21.6°C | 16.9°C | 30.7°C | 14.7°C | 28 mm | 75% | 1.6 m/s | 5.6 |
| 2019 | 26.3°C | 20.2°C | 14.2°C | 30.8°C | 10.3°C | 2 mm | 63% | 1.4 m/s | 6.7 |
| 2018 | 27.0°C | 21.4°C | 15.8°C | 31.9°C | 12.6°C | 5 mm | 68% | 1.3 m/s | 6.5 |
| 2017 | 27.5°C | 21.8°C | 16.1°C | 33.3°C | 12.7°C | 11 mm | 69% | 1.3 m/s | 6.3 |
| 2016 🔥 | 28.6°C | 23.4°C | 18.3°C | 33.6°C | 16.6°C | 36 mm | 76% | 1.2 m/s | 5.5 |
| 2015 | 26.5°C | 21.0°C | 15.5°C | 30.9°C | 13.0°C | 12 mm | 70% | 1.2 m/s | 5.9 |
| 2014 | 25.0°C | 19.8°C | 14.5°C | 28.2°C | 10.5°C | 8 mm | 76% | 1 m/s | 6.6 |
| 2013 | 26.2°C | 20.8°C | 15.5°C | 30.8°C | 13.4°C | 48 mm | 75% | 1.1 m/s | 6.3 |
| 2012 | 25.2°C | 20.2°C | 15.3°C | 29.4°C | 12.8°C | 20 mm | 79% | 1 m/s | 5.8 |
| 2011 | 24.7°C | 19.5°C | 14.3°C | 33.2°C | 9.1°C | 35 mm | 75% | 1.2 m/s | 6.2 |
| 2010 | 25.3°C | 21.8°C | 18.3°C | 26.7°C | 16.0°C | 120 mm | 88% | 1.1 m/s | 5 |
| 2009 | 27.9°C | 21.9°C | 16.0°C | 33.0°C | 14.1°C | 3 mm | 70% | 1.2 m/s | 6.3 |
| 2008 | 25.7°C | 21.1°C | 16.5°C | 29.5°C | 15.5°C | 69 mm | 80% | 1.2 m/s | 5.7 |
| 2007 | 25.0°C | 19.7°C | 14.4°C | 29.0°C | 12.3°C | 17 mm | 76% | 1 m/s | 6.4 |
| 2006 | 21.9°C | 18.0°C | 14.1°C | 24.9°C | 7.3°C | 122 mm | 83% | 1.2 m/s | 5.9 |
| 2005 | 24.1°C | 19.6°C | 15.1°C | 28.3°C | 12.6°C | 9 mm | 81% | 1 m/s | 6 |
| 2004 | 24.3°C | 19.6°C | 15.0°C | 27.9°C | 13.0°C | 34 mm | 77% | 1.2 m/s | 5.8 |
| 2003 | 26.2°C | 20.5°C | 14.8°C | 32.5°C | 11.9°C | 8 mm | 70% | 1.1 m/s | 6.6 |
| 2002 | 27.2°C | 21.1°C | 15.1°C | 31.6°C | 11.1°C | 22 mm | 71% | 1.1 m/s | 6.3 |
| 2001 | 26.4°C | 21.3°C | 16.2°C | 32.5°C | 13.3°C | 43 mm | 75% | 1.3 m/s | 5.7 |
| 2000 | 25.8°C | 20.6°C | 15.5°C | 30.7°C | 11.6°C | 12 mm | 75% | 1.2 m/s | 6.1 |
| 1999 | 23.7°C | 19.4°C | 15.1°C | 28.5°C | 13.4°C | 69 mm | 81% | 1.2 m/s | 5.9 |
| 1998 🌧️ | 23.7°C | 20.6°C | 17.4°C | 25.7°C | 14.4°C | 182 mm | 89% | 1.2 m/s | 5.3 |
| 1997 | 24.9°C | 20.0°C | 15.2°C | 29.7°C | 13.3°C | 27 mm | 80% | 1 m/s | 6.1 |
| 1996 | 26.5°C | 20.0°C | 13.5°C | 34.3°C | 9.4°C | 7 mm | 69% | 1.1 m/s | 6.6 |
| 1995 | 23.7°C | 19.4°C | 15.1°C | 28.9°C | 13.7°C | 13 mm | 83% | 1 m/s | 6.2 |
| 1994 | 23.3°C | 18.6°C | 13.9°C | 30.9°C | 11.6°C | 27 mm | 80% | 1 m/s | 6.2 |
| 1993 | 23.5°C | 19.5°C | 15.4°C | 27.7°C | 13.2°C | 104 mm | 83% | 1.1 m/s | 5.5 |
| 1992 | 28.3°C | 22.8°C | 17.4°C | 33.6°C | 14.1°C | 48 mm | 74% | 1 m/s | 5.9 |
| 1991 | 27.6°C | 21.1°C | 14.6°C | 32.4°C | 10.9°C | 0 mm | 64% | 1.1 m/s | 6.5 |
| 1990 ❄️ | 22.0°C | 17.6°C | 13.2°C | 25.1°C | 8.1°C | 101 mm | 79% | 1.3 m/s | 5.5 |
| 1989 | 25.3°C | 20.0°C | 14.7°C | 30.9°C | 12.0°C | 16 mm | 74% | 1.1 m/s | 6.1 |
| 1988 | 24.8°C | 19.9°C | 15.1°C | 29.5°C | 9.4°C | 48 mm | 79% | 1.1 m/s | 5.9 |
| 1987 | 22.4°C | 18.7°C | 15.1°C | 26.2°C | 12.4°C | 86 mm | 85% | 1.2 m/s | 5.3 |
| 1986 | 25.9°C | 21.0°C | 16.2°C | 32.2°C | 13.8°C | 46 mm | 79% | 1 m/s | 5.8 |
| 1985 | 25.8°C | 19.9°C | 13.9°C | 32.0°C | 7.9°C | 31 mm | 70% | 1.1 m/s | 6.3 |
| 1984 | 27.6°C | 21.8°C | 16.0°C | 31.0°C | 12.6°C | 5 mm | 71% | 0.9 m/s | 6.1 |
| 1983 | 25.0°C | 20.5°C | 16.0°C | 29.2°C | 12.3°C | 89 mm | 82% | 1.1 m/s | — |
| 1982 | 23.1°C | 18.6°C | 14.1°C | 29.8°C | 11.3°C | 37 mm | 79% | 1 m/s | — |
| 1981 | 22.9°C | 18.9°C | 14.9°C | 29.6°C | 12.3°C | 143 mm | 83% | 1.4 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 25.5°C with lows near 15.5°C (mean 20.5°C), based on 45 years of NASA POWER data.
September averages 42 mm of rainfall in Atherton, one of the drier months. The wettest on record was 182 mm in 1998.
The hottest September reached 34.3°C in 1996. The coldest dipped to 7.3°C in 2006.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2°C. Daytime highs moved from 24.9°C to 26.9°C and overnight lows from 15°C to 16.9°C over the same span.
September is one of the cooler months of the year in Atherton and one of the drier months, so plan for around 25.5°C daytime highs and 15.5°C at night.
Not quite — September is the 5th coolest month in Atherton, averaging 20.5°C.
For September in Atherton, pack light layers you can adjust through the day, with typical highs of 25.5°C and lows of 15.5°C.
Relative humidity in September averages 76% — quite humid.
Average wind speed in September is 1.2 m/s. The windiest September on record averaged 1.6 m/s (2020).
The wettest September on record was 1998 with 182 mm. On average, September sees 42 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 Atherton 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.
