September is one of the warmer months of the year in Brentwood, with average highs near 28.9°C and lows around 16.1°C (mean 22.5°C). It is one of the drier months, averaging 93 mm of rainfall and 68% relative humidity across the period.
September is one of the warmer months of the year in Brentwood. Across 45 years of records, the warmest September in Brentwood was 2019 — when the month averaged 27.2°C — while the coldest were 1982, 1989 and 2011 at 20.5°C. Typical September days reach 28.9°C with nights near 16.1°C. The long-term trend is warming, about 0.3°C per decade.
September is one of the drier months in Brentwood, averaging 93 mm of rainfall. The wettest September on record was 2009 with 211 mm, while the driest was 2019 at 11 mm.
Relative humidity in Brentwood during September averages 68%. The most humid September was 1989 at 81%, and the least humid was 1999 at 42%.
September receives about 4.7 kWh/m²/day of solar energy in Brentwood. The sunniest September was 2019 at 5.6 kWh/m²/day, and the cloudiest was 1989 at 3.9.
Average wind speed in Brentwood during September is 1.4 m/s. The windiest Septembers were 2000, 2004 and 2006 at 1.7 m/s, while the calmest were 2021, 2023 and 2025, among others at 1.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 21.8°C | 22.5°C | 22.6°C | 23.0°C | 22.5°C | +0.7°C |
| Avg High | 28.1°C | 29.2°C | 28.8°C | 29.3°C | 28.8°C | +0.7°C |
| Avg Low | 15.5°C | 15.8°C | 16.3°C | 16.8°C | 16.2°C | +0.7°C |
| Avg Rain | 94 mm | 89 mm | 100 mm | 81 mm | 106 mm | +12 mm |
September temperatures in Brentwood have risen by about 1.4°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 4°C (1983) to a record high of 39.7°C (1990).
Rainfall in September is one of the drier months, averaging 93 mm, with a wettest year of 211 mm.
One of the best times to visit Brentwood
September is one of the best times to visit Brentwood. Expect days averaging 28.9°C and nights around 16.1°C (mean 22.5°C) — warmer than Brentwood's yearly average — with higher rainfall (93 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 | 30.9°C | 23.8°C | 16.8°C | 34.7°C | 10.5°C | 119 mm | 63% | 1.2 m/s | 5 |
| 2024 | 29.9°C | 23.6°C | 17.4°C | 35.4°C | 9.4°C | 161 mm | 66% | 1.4 m/s | 4.2 |
| 2023 | 30.2°C | 23.3°C | 16.5°C | 34.1°C | 11.8°C | 47 mm | 64% | 1.2 m/s | 4.9 |
| 2022 | 28.7°C | 22.0°C | 15.4°C | 36.9°C | 7.1°C | 75 mm | 68% | 1.4 m/s | 5.2 |
| 2021 | 26.6°C | 21.2°C | 15.8°C | 30.8°C | 8.7°C | 128 mm | 79% | 1.2 m/s | 4.9 |
| 2020 | 26.3°C | 20.8°C | 15.4°C | 31.4°C | 8.2°C | 104 mm | 79% | 1.4 m/s | 4.4 |
| 2019 🔥 | 34.4°C | 27.2°C | 20.0°C | 37.2°C | 15.5°C | 11 mm | 59% | 1.2 m/s | 5.6 |
| 2018 | 30.4°C | 25.0°C | 19.6°C | 36.5°C | 14.1°C | 155 mm | 75% | 1.3 m/s | 4.2 |
| 2017 | 26.4°C | 20.7°C | 15.0°C | 30.9°C | 9.1°C | 83 mm | 76% | 1.4 m/s | 4.9 |
| 2016 | 30.8°C | 24.2°C | 17.6°C | 34.7°C | 8.8°C | 52 mm | 67% | 1.3 m/s | 5.5 |
| 2015 | 29.8°C | 23.2°C | 16.7°C | 35.2°C | 9.4°C | 58 mm | 67% | 1.2 m/s | 4.8 |
| 2014 | 28.8°C | 22.6°C | 16.3°C | 32.5°C | 8.2°C | 24 mm | 70% | 1.3 m/s | 4.6 |
| 2013 | 28.6°C | 22.5°C | 16.4°C | 34.1°C | 9.6°C | 83 mm | 74% | 1.2 m/s | 5.1 |
| 2012 | 27.0°C | 21.2°C | 15.3°C | 33.3°C | 4.9°C | 142 mm | 73% | 1.4 m/s | 4.7 |
| 2011 | 26.1°C | 20.5°C | 15.0°C | 39.0°C | 9.5°C | 170 mm | 72% | 1.6 m/s | 4.3 |
| 2010 | 30.7°C | 23.4°C | 16.1°C | 36.2°C | 9.4°C | 32 mm | 60% | 1.4 m/s | 5.2 |
| 2009 🌧️ | 26.7°C | 22.1°C | 17.5°C | 31.0°C | 8.2°C | 211 mm | 81% | 1.2 m/s | 4 |
| 2008 | 30.2°C | 23.5°C | 16.9°C | 34.6°C | 11.4°C | 27 mm | 64% | 1.6 m/s | 4.7 |
| 2007 | 31.0°C | 24.4°C | 17.8°C | 36.3°C | 9.9°C | 74 mm | 61% | 1.3 m/s | 4.9 |
| 2006 | 27.3°C | 20.9°C | 14.5°C | 33.2°C | 6.6°C | 95 mm | 68% | 1.7 m/s | 4.7 |
| 2005 | 30.2°C | 23.6°C | 17.1°C | 33.8°C | 7.0°C | 53 mm | 69% | 1.3 m/s | 5.3 |
| 2004 | 28.1°C | 22.0°C | 15.9°C | 32.8°C | 9.2°C | 85 mm | 73% | 1.7 m/s | 4.9 |
| 2003 | 26.7°C | 20.8°C | 14.8°C | 32.8°C | 4.7°C | 160 mm | 73% | 1.4 m/s | 5.2 |
| 2002 | 30.7°C | 24.4°C | 18.1°C | 36.9°C | 9.6°C | 162 mm | 66% | 1.5 m/s | 4.4 |
| 2001 | 28.1°C | 21.4°C | 14.6°C | 33.7°C | 4.4°C | 63 mm | 65% | 1.6 m/s | 4.8 |
| 2000 | 29.2°C | 22.5°C | 15.9°C | 34.7°C | 6.1°C | 71 mm | 62% | 1.7 m/s | 4.5 |
| 1999 | 30.8°C | 22.9°C | 15.0°C | 38.6°C | 6.4°C | 38 mm | 42% | 1.5 m/s | 5.3 |
| 1998 | 33.5°C | 26.0°C | 18.5°C | 38.4°C | 10.5°C | 27 mm | 54% | 1.3 m/s | 5.2 |
| 1997 | 29.5°C | 22.4°C | 15.4°C | 35.7°C | 9.1°C | 115 mm | 64% | 1.4 m/s | 4.9 |
| 1996 | 27.0°C | 20.9°C | 14.9°C | 32.2°C | 7.1°C | 155 mm | 72% | 1.4 m/s | 4.5 |
| 1995 | 28.4°C | 21.7°C | 14.9°C | 34.1°C | 6.3°C | 96 mm | 65% | 1.4 m/s | 4.4 |
| 1994 | 28.3°C | 21.2°C | 14.0°C | 33.3°C | 8.5°C | 73 mm | 66% | 1.3 m/s | 4.9 |
| 1993 | 28.9°C | 22.0°C | 15.1°C | 35.7°C | 4.8°C | 90 mm | 65% | 1.6 m/s | 4.5 |
| 1992 | 26.4°C | 21.0°C | 15.6°C | 32.0°C | 4.3°C | 126 mm | 77% | 1.6 m/s | 4.1 |
| 1991 | 28.6°C | 22.6°C | 16.5°C | 35.5°C | 4.2°C | 81 mm | 67% | 1.4 m/s | 4.8 |
| 1990 | 31.0°C | 24.3°C | 17.6°C | 39.7°C | 5.8°C | 83 mm | 60% | 1.3 m/s | 4.9 |
| 1989 | 25.6°C | 20.5°C | 15.3°C | 32.2°C | 4.2°C | 189 mm | 81% | 1.4 m/s | 3.9 |
| 1988 | 28.8°C | 22.7°C | 16.7°C | 34.7°C | 8.4°C | 132 mm | 72% | 1.6 m/s | 4 |
| 1987 | 29.2°C | 22.6°C | 16.0°C | 34.1°C | 10.6°C | 97 mm | 61% | 1.3 m/s | 4.5 |
| 1986 | 28.7°C | 23.3°C | 17.9°C | 32.9°C | 12.0°C | 124 mm | 76% | 1.5 m/s | 4.4 |
| 1985 | 28.4°C | 21.5°C | 14.7°C | 33.9°C | 6.3°C | 86 mm | 63% | 1.6 m/s | 5.1 |
| 1984 | 28.3°C | 21.2°C | 14.2°C | 35.8°C | 6.6°C | 23 mm | 59% | 1.6 m/s | 4.6 |
| 1983 | 29.7°C | 23.0°C | 16.2°C | 36.3°C | 4.0°C | 38 mm | 59% | 1.5 m/s | — |
| 1982 ❄️ | 26.4°C | 20.5°C | 14.6°C | 31.5°C | 5.7°C | 81 mm | 75% | 1.3 m/s | — |
| 1981 | 27.7°C | 20.7°C | 13.6°C | 32.6°C | 6.5°C | 77 mm | 66% | 1.4 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 28.9°C with lows near 16.1°C (mean 22.5°C), based on 45 years of NASA POWER data.
September averages 93 mm of rainfall in Brentwood, one of the drier months. The wettest on record was 211 mm in 2009.
The hottest September reached 39.7°C in 1990. The coldest dipped to 4°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.4°C. Daytime highs moved from 28.1°C to 29.3°C and overnight lows from 14.7°C to 16.4°C over the same span.
September is one of the warmer months of the year in Brentwood and one of the drier months, so plan for around 28.9°C daytime highs and 16.1°C at night.
Not quite — September is the 9th coolest month in Brentwood, averaging 22.5°C.
For September in Brentwood, pack light layers you can adjust through the day, with typical highs of 28.9°C and lows of 16.1°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 68% — moderately humid.
Average wind speed in September is 1.4 m/s. The windiest September on record averaged 1.7 m/s (2000).
The wettest September on record was 2009 with 211 mm. On average, September sees 93 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 Brentwood 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.
