September is one of the warmer months of the year in Santa Rosa, with average highs near 30.5°C and lows around 13.3°C (mean 21.9°C). It is one of the drier months, averaging 7 mm of rainfall and 47% relative humidity across the period.
September is one of the warmer months of the year in Santa Rosa. Across 45 years of records, the warmest September in Santa Rosa was 2020 — when the month averaged 24°C — while the coldest was 1986 at 17.9°C. Typical September days reach 30.5°C with nights near 13.3°C. The long-term trend is warming, about 0.2°C per decade.
September is one of the drier months in Santa Rosa, averaging 7 mm of rainfall. The wettest September on record was 1989 with 60 mm, while the driest were 2016, 2020 and 2024, among others at 0 mm.
Relative humidity in Santa Rosa during September averages 47%. The most humid September was 2023 at 59%, and the least humid was 1984 at 33%.
September receives about 5.8 kWh/m²/day of solar energy in Santa Rosa. The sunniest September was 2004 at 6.2 kWh/m²/day, and the cloudiest were 2020 and 2025 at 5.2.
Average wind speed in Santa Rosa during September is 1.6 m/s. The windiest September was 2013 at 2 m/s, while the calmest was 1991 at 1.3 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 21.1°C | 22.2°C | 22.0°C | 22.0°C | 22.6°C | +1.5°C |
| Avg High | 29.5°C | 31.0°C | 30.6°C | 30.5°C | 30.9°C | +1.4°C |
| Avg Low | 12.6°C | 13.4°C | 13.3°C | 13.5°C | 14.2°C | +1.6°C |
| Avg Rain | 21 mm | 3 mm | 3 mm | 5 mm | 7 mm | -13 mm |
September temperatures in Santa Rosa have risen by about 0.9°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 7°C (2019) to a record high of 45.8°C (2022).
Rainfall in September is one of the drier months, averaging 7 mm, with a wettest year of 60 mm.
One of the best times to visit Santa Rosa
September is one of the best times to visit Santa Rosa. Expect days averaging 30.5°C and nights around 13.3°C (mean 21.9°C) — warmer than Santa Rosa's yearly average — with low rainfall (7 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 | 30.0°C | 22.4°C | 14.7°C | 38.3°C | 10.7°C | 6 mm | 56% | 1.7 m/s | 5.2 |
| 2024 | 31.8°C | 22.9°C | 14.0°C | 37.6°C | 10.4°C | 0 mm | 45% | 1.7 m/s | 5.9 |
| 2023 | 28.4°C | 20.5°C | 12.5°C | 34.5°C | 8.9°C | 4 mm | 59% | 1.7 m/s | 5.6 |
| 2022 | 31.5°C | 23.3°C | 15.0°C | 45.8°C | 10.3°C | 30 mm | 49% | 1.6 m/s | 5.5 |
| 2021 | 31.0°C | 22.4°C | 13.9°C | 38.7°C | 9.6°C | 3 mm | 45% | 1.7 m/s | 5.7 |
| 2020 🔥 | 32.8°C | 24.0°C | 15.3°C | 44.3°C | 11.5°C | 0 mm | 44% | 1.7 m/s | 5.2 |
| 2019 | 29.9°C | 21.7°C | 13.6°C | 37.6°C | 7.0°C | 4 mm | 51% | 1.9 m/s | 6 |
| 2018 | 30.4°C | 21.3°C | 12.1°C | 36.8°C | 8.1°C | 1 mm | 46% | 1.6 m/s | 6 |
| 2017 | 30.6°C | 22.9°C | 15.1°C | 42.8°C | 8.2°C | 2 mm | 47% | 1.7 m/s | 5.4 |
| 2016 | 30.7°C | 21.9°C | 13.1°C | 37.6°C | 9.8°C | 0 mm | 45% | 1.7 m/s | 6.1 |
| 2015 | 30.5°C | 22.3°C | 14.1°C | 39.1°C | 9.6°C | 6 mm | 44% | 1.7 m/s | 5.5 |
| 2014 | 29.5°C | 21.5°C | 13.5°C | 37.3°C | 10.2°C | 14 mm | 58% | 1.7 m/s | 5.6 |
| 2013 | 28.7°C | 20.7°C | 12.6°C | 37.6°C | 8.5°C | 16 mm | 56% | 2 m/s | 5.8 |
| 2012 | 31.0°C | 21.7°C | 12.4°C | 36.8°C | 9.7°C | 0 mm | 44% | 1.5 m/s | 6 |
| 2011 | 32.4°C | 23.5°C | 14.6°C | 39.2°C | 10.0°C | 1 mm | 42% | 1.5 m/s | 5.8 |
| 2010 | 31.2°C | 22.3°C | 13.5°C | 39.6°C | 9.3°C | 2 mm | 45% | 1.6 m/s | 6 |
| 2009 | 32.7°C | 23.7°C | 14.8°C | 40.2°C | 8.1°C | 7 mm | 43% | 1.6 m/s | 5.9 |
| 2008 | 31.3°C | 22.4°C | 13.4°C | 39.5°C | 8.0°C | 0 mm | 44% | 1.5 m/s | 5.9 |
| 2007 | 28.0°C | 20.1°C | 12.2°C | 38.0°C | 8.3°C | 3 mm | 54% | 1.7 m/s | 5.7 |
| 2006 | 30.7°C | 21.8°C | 13.0°C | 38.5°C | 9.0°C | 0 mm | 43% | 1.6 m/s | 5.9 |
| 2005 | 28.6°C | 20.0°C | 11.5°C | 34.5°C | 8.5°C | 1 mm | 50% | 1.5 m/s | 5.9 |
| 2004 | 31.5°C | 22.9°C | 14.3°C | 39.5°C | 7.5°C | 3 mm | 41% | 1.7 m/s | 6.2 |
| 2003 | 32.1°C | 23.2°C | 14.2°C | 39.9°C | 9.6°C | 1 mm | 44% | 1.8 m/s | 5.9 |
| 2002 | 30.9°C | 22.4°C | 13.8°C | 38.7°C | 8.7°C | 0 mm | 42% | 1.7 m/s | 6.1 |
| 2001 | 30.5°C | 21.7°C | 12.9°C | 36.1°C | 9.8°C | 7 mm | 51% | 1.5 m/s | 5.8 |
| 2000 | 30.1°C | 21.6°C | 13.2°C | 39.6°C | 8.3°C | 9 mm | 49% | 1.6 m/s | 5.6 |
| 1999 | 32.1°C | 22.9°C | 13.7°C | 36.4°C | 10.2°C | 2 mm | 40% | 1.5 m/s | 5.8 |
| 1998 | 30.4°C | 22.3°C | 14.2°C | 42.0°C | 9.9°C | 5 mm | 52% | 1.6 m/s | 5.5 |
| 1997 | 30.7°C | 22.1°C | 13.5°C | 36.4°C | 8.7°C | 6 mm | 49% | 1.8 m/s | 6 |
| 1996 | 29.6°C | 21.1°C | 12.7°C | 34.3°C | 9.4°C | 2 mm | 44% | 1.6 m/s | 5.9 |
| 1995 | 30.7°C | 21.7°C | 12.7°C | 38.4°C | 9.4°C | 0 mm | 52% | 1.6 m/s | 6 |
| 1994 | 30.6°C | 21.9°C | 13.2°C | 36.2°C | 9.8°C | 1 mm | 49% | 1.5 m/s | 5.7 |
| 1993 | 31.6°C | 22.4°C | 13.2°C | 37.6°C | 8.8°C | 2 mm | 40% | 1.4 m/s | 6 |
| 1992 | 30.8°C | 22.2°C | 13.5°C | 35.2°C | 10.0°C | 2 mm | 44% | 1.7 m/s | 5.9 |
| 1991 | 32.6°C | 23.3°C | 14.0°C | 38.2°C | 9.7°C | 0 mm | 43% | 1.3 m/s | 5.8 |
| 1990 | 30.8°C | 21.9°C | 13.0°C | 36.6°C | 9.8°C | 6 mm | 50% | 1.6 m/s | 6 |
| 1989 🌧️ | 27.7°C | 19.5°C | 11.3°C | 34.1°C | 8.5°C | 60 mm | 55% | 1.4 m/s | 5.4 |
| 1988 | 32.1°C | 22.7°C | 13.4°C | 43.8°C | 8.5°C | 0 mm | 34% | 1.7 m/s | 5.8 |
| 1987 | 32.0°C | 22.6°C | 13.1°C | 38.6°C | 9.3°C | 0 mm | 41% | 1.6 m/s | 5.9 |
| 1986 ❄️ | 25.5°C | 17.9°C | 10.4°C | 36.1°C | 7.1°C | 36 mm | 59% | 1.7 m/s | 5.3 |
| 1985 | 26.6°C | 18.8°C | 10.9°C | 34.1°C | 7.3°C | 24 mm | 57% | 1.5 m/s | 5.4 |
| 1984 | 32.5°C | 23.7°C | 15.0°C | 38.5°C | 9.5°C | 4 mm | 33% | 1.7 m/s | 5.7 |
| 1983 | 30.4°C | 22.1°C | 13.7°C | 38.1°C | 10.1°C | 18 mm | 50% | 1.5 m/s | — |
| 1982 | 28.4°C | 20.5°C | 12.6°C | 38.2°C | 7.8°C | 31 mm | 47% | 1.7 m/s | — |
| 1981 | 30.5°C | 21.8°C | 13.0°C | 36.0°C | 7.8°C | 12 mm | 45% | 1.7 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 30.5°C with lows near 13.3°C (mean 21.9°C), based on 45 years of NASA POWER data.
September averages 7 mm of rainfall in Santa Rosa, one of the drier months. The wettest on record was 60 mm in 1989.
The hottest September reached 45.8°C in 2022. The coldest dipped to 7°C in 2019.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 0.9°C. Daytime highs moved from 29.7°C to 30.5°C and overnight lows from 13°C to 14°C over the same span.
September is one of the warmer months of the year in Santa Rosa and one of the drier months, so plan for around 30.5°C daytime highs and 13.3°C at night.
Not quite — September is the 10th coolest month in Santa Rosa, averaging 21.9°C.
For September in Santa Rosa, pack light, breathable clothing and sun protection, with typical highs of 30.5°C and lows of 13.3°C.
Relative humidity in September averages 47% — relatively dry.
Average wind speed in September is 1.6 m/s. The windiest September on record averaged 2 m/s (2013).
The wettest September on record was 1989 with 60 mm. On average, September sees 7 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 Santa Rosa 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.
