San Francisco weather in September
Temperature, sea and sunshine in September: long-term averages from 30 years of weather data, not a forecast.
Holiday weather in September
Excellent
Best time to visit: April – October
What is the weather like in San Francisco in September?
In September, San Francisco is warm: daytime highs average 23 °C, and nights cool down to about 13 °C. The sea averages 14.6 °C – swimming is only for the hardy. With around 9 hours of sunshine a day, there is plenty of sun. It hardly ever rains. All in all, September is an excellent month for a holiday in San Francisco.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 100 | 100 | 95 |
| Day | 22° | 23° | 21° |
| Night | 13° | 13° | 12° |
| Sea | 15° | 15° | 14° |
| Sun | 10 h | 9 h | 8 h |
| Rain days | 0 | 1 | 3 |
More details for September
- Daylight
- 12 h 29 min06:50 – 19:20
- UV index
- 7 · highclear sky, noon (estimate)All months
- Muggy days
- 0 daysdew point 18 °C or more
- Wind
- 15 km/haverage daily peak
- Cloud cover
- 34 %on average
- Hot days
- 2 days30 °C or more
- Time zone
- UTC−7America/Los_Angeles
How the score comes together
- Temperatureweight 50 %100 %
- Sunshineweight 20 %100 %
- Few rainy daysweight 30 %100 %
Each factor is rated from 0 to 100 % and weighted for the travel style “City break”.
What to pack in September
- Sunscreen
- Sunglasses & sun hat
- A jumper for the evenings
San Francisco in September: quick answers
Is San Francisco hot in September?
Warm rather than hot: in September, daytime highs in San Francisco average 23 °C and nights cool to about 13 °C. On about 2 days the thermometer climbs to 30 °C or more.
Can you swim in San Francisco in September?
Only if you don't mind cold water: in September the sea averages just 14.6 °C. Comfortable swimming temperatures are not reached at any time of year.
Does it rain much in San Francisco in September?
It hardly ever rains.
San Francisco month by month
The whole year in San FranciscoAll destinations: USAWhere to go in SeptemberSea temperature in September
Climate averages 1996–2025, not a forecast. Data: Copernicus ERA5 / ERA5-Land via Open-Meteo.com (CC BY 4.0), NOAA OISST, WMO 1991–2020 (NOAA NCEI), GeoNames (CC BY 4.0)