San Francisco weather in September
September in San Francisco: warm, dry, with clean air — an excellent time to visit.
#4 of 12 months in San Francisco · #37 of 604 destinations to visit in September · comfort 92/100 (tier S)
Updated June 2026 · climate normals from ERA5 reanalysis
San Francisco climate normals — September
| Daytime high | 24°C / 75°F | 🌤 warm |
|---|---|---|
| Nighttime low | 14°C / 57°F | |
| Feels like (high) | 24°C / 75°F | |
| Rainfall | 4 mm / 0.1 in | ☀️ dry |
| Rainy days | 0 days | |
| Humidity | 77% | 💦 very humid |
| Dew point | 13°C / 56°F | |
| Sunshine | 11.3 h/day | |
| Daylight | 12.4 h | |
| Wind | 16 km/h / 10 mph | |
| Air quality (US AQI) | 35 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
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San Francisco in September — FAQ
- Is September a good time to visit San Francisco?
- September in San Francisco: warm, dry, with clean air — an excellent time to visit. It ranks #4 of 12 months for San Francisco on SeasonMap's comfort score (92/100).
- What is the weather like in San Francisco in September?
- In September, San Francisco averages a daily high of 23.7°C and a low of 14.1°C, with about 3.5 mm of rain over roughly 0.4 rainy days.
- What is the air quality in San Francisco in September?
- San Francisco has a mean US Air Quality Index of about 35 in September.