Climate averages 1991–2020
Santa Rosa, United States weather
in September.
A hot, very dry month: the 3rd warmest and the 3rd driest of the year. Meets the pleasant-weather rule
Long-term climate patterns, not a forecast for a particular trip.
September is a hot month in Santa Rosa, United States: daytime highs average 28.4°C and nights cool to about 13.6°C. By daytime temperature it is the 3rd warmest of the 12 months.
Expect about 3.1 mm of rain on fewer than one day, which makes September a very dry month (the 3rd driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 28 min on an average September day.
The nearest other city in this atlas is Napa (41 km away). In September its highs average 29.5°C, 1.1°C warmer than Santa Rosa, United States, with 2.0 mm of rain.
Among the 498 cities listed in the United States, Santa Rosa, United States ranks joint 191st of 498 for the warmest September highs and joint 40th of 498 for the driest September (rainfall, lowest first). The mean September high of those 498 cities is 26.9°C; Santa Rosa, United States is 1.5°C warmer than that mean.
From September to October, average highs fall by 4.0°C to 24.4°C, and monthly rainfall rises from 3.1 mm to 34 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Santa Rosa, United States climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 14.4°C4.2°C | 4.2°C | 145 | 10.3 | 9.810 h |
| February | 15.7°C5.0°C | 5.0°C | 149 | 9.5 | 10.711 h |
| March | 17.5°C6.3°C | 6.3°C | 112 | 9.5 | 11.912 h |
| April | 19.8°C7.8°C | 7.8°C | 49 | 5.6 | 13.213 h |
| May | 23.6°C10.6°C | 10.6°C | 28 | 3.6 | 14.214 h |
| June | 27.8°C13.1°C | 13.1°C | 7.0 | 1.2 | 14.815 h |
| July | 29.6°C14.1°C | 14.1°C | 0.4 | 0.1 | 14.615 h |
| August | 29.5°C14.3°C | 14.3°C | 1.1 | 0.2 | 13.714 h |
| September, selected | 28.4°C13.6°C | 13.6°C | 3.1 | 0.6 | 12.512 h |
| October | 24.4°C11.2°C | 11.2°C | 34 | 3.2 | 11.211 h |
| November | 18.0°C7.0°C | 7.0°C | 75 | 6.2 | 10.110 h |
| December | 14.0°C4.2°C | 4.2°C | 150 | 10.2 | 9.510 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Napa in SeptemberUnited States · 41 kmHigh 29.5°C · Low 14.6°C · 2.0 mm rain
- Vallejo in SeptemberUnited States · 55 kmHigh 28.2°C · Low 13.5°C · 1.8 mm rain
- Fairfield in SeptemberUnited States · 63 kmHigh 28.9°C · Low 14.3°C · 1.5 mm rain
- Vacaville in SeptemberUnited States · 64 kmHigh 30.4°C · Low 15.3°C · 1.5 mm rain
- Berkeley in SeptemberUnited States · 74 kmHigh 26.2°C · Low 13.2°C · 1.4 mm rain
- San Francisco in SeptemberUnited States · 78 kmHigh 22.7°C · Low 13.0°C · 1.5 mm rain
- Concord (California), United States in SeptemberUnited States · 79 kmHigh 28.2°C · Low 14.1°C · 1.5 mm rain
- Oakland in SeptemberUnited States · 81 kmHigh 26.2°C · Low 13.8°C · 1.4 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Santa Rosa) is explained once on the Santa Rosa, United States year overview and on the Sources, method and limits page.