September is one of the warmer months of the year in San Francisco, with average highs near 24.1°C and lows around 12.9°C (mean 18.5°C). It is one of the drier months, averaging 7 mm of rainfall and 70% relative humidity across the period.
September is one of the warmer months of the year in San Francisco. Across 45 years of records, the warmest September in San Francisco was 2017 — when the month averaged 20.4°C — while the coldest was 1986 at 16.1°C. Typical September days reach 24.1°C with nights near 12.9°C. The long-term trend is warming, about 0.2°C per decade.
September is one of the drier months in San Francisco, averaging 7 mm of rainfall. The wettest September on record was 1989 with 47 mm, while the driest were 1988, 2002 and 2020, among others at 0 mm.
Relative humidity in San Francisco during September averages 70%. The most humid September was 2023 at 78%, and the least humid was 1984 at 55%.
September receives about 5 kWh/m²/day of solar energy in San Francisco. The sunniest September was 1997 at 5.9 kWh/m²/day, and the cloudiest was 1991 at 4.1.
Average wind speed in San Francisco during September is 2 m/s. The windiest September was 2019 at 2.5 m/s, while the calmest was 1991 at 1.7 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 18.2°C | 18.5°C | 18.3°C | 18.6°C | 19.2°C | +1°C |
| Avg High | 23.9°C | 24.2°C | 24.0°C | 24.1°C | 24.5°C | +0.6°C |
| Avg Low | 12.4°C | 12.7°C | 12.6°C | 13.2°C | 13.8°C | +1.4°C |
| Avg Rain | 17 mm | 3 mm | 5 mm | 4 mm | 6 mm | -11 mm |
September temperatures in San Francisco have risen by about 0.3°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 9.2°C (1985) to a record high of 39°C (2020).
Rainfall in September is one of the drier months, averaging 7 mm, with a wettest year of 47 mm.
One of the best times to visit San Francisco
September is one of the best times to visit San Francisco. Expect days averaging 24.1°C and nights around 12.9°C (mean 18.5°C) — warmer than San Francisco'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 | 24.2°C | 19.5°C | 14.7°C | 34.6°C | 12.5°C | 7 mm | 76% | 2.2 m/s | 4.7 |
| 2024 | 24.6°C | 18.9°C | 13.2°C | 32.8°C | 11.9°C | 1 mm | 71% | 2.1 m/s | 5.1 |
| 2023 | 22.5°C | 17.7°C | 13.0°C | 26.2°C | 10.7°C | 3 mm | 78% | 2.4 m/s | 5 |
| 2022 | 25.6°C | 20.0°C | 14.5°C | 38.0°C | 11.7°C | 22 mm | 69% | 2.3 m/s | 5.2 |
| 2021 | 24.0°C | 18.5°C | 13.0°C | 30.5°C | 11.1°C | 3 mm | 70% | 2.3 m/s | 5 |
| 2020 | 26.1°C | 20.3°C | 14.4°C | 39.0°C | 12.0°C | 0 mm | 68% | 2 m/s | 4.9 |
| 2019 | 24.8°C | 19.5°C | 14.2°C | 34.7°C | 9.7°C | 5 mm | 70% | 2.5 m/s | 5.7 |
| 2018 | 23.5°C | 17.7°C | 12.0°C | 29.7°C | 10.3°C | 1 mm | 72% | 2.3 m/s | 5.2 |
| 2017 🔥 | 25.7°C | 20.4°C | 15.1°C | 38.0°C | 10.9°C | 3 mm | 67% | 2 m/s | 5 |
| 2016 | 23.9°C | 18.3°C | 12.7°C | 33.5°C | 11.1°C | 1 mm | 69% | 2.2 m/s | 5.3 |
| 2015 | 24.8°C | 19.4°C | 14.0°C | 33.5°C | 11.6°C | 4 mm | 65% | 2.1 m/s | 5.2 |
| 2014 | 24.0°C | 19.1°C | 14.1°C | 32.0°C | 11.7°C | 13 mm | 77% | 2 m/s | 4.9 |
| 2013 | 23.3°C | 18.3°C | 13.3°C | 30.9°C | 10.5°C | 14 mm | 73% | 2.3 m/s | 5.4 |
| 2012 | 21.9°C | 16.4°C | 10.9°C | 31.3°C | 9.8°C | 1 mm | 75% | 2 m/s | 4.9 |
| 2011 | 24.0°C | 18.4°C | 12.7°C | 31.8°C | 10.6°C | 2 mm | 71% | 1.8 m/s | 4.9 |
| 2010 | 24.6°C | 18.6°C | 12.6°C | 34.1°C | 9.9°C | 2 mm | 67% | 1.9 m/s | 5.3 |
| 2009 | 25.3°C | 19.3°C | 13.4°C | 32.9°C | 9.3°C | 8 mm | 69% | 2 m/s | 5.2 |
| 2008 | 24.5°C | 18.6°C | 12.7°C | 33.1°C | 10.3°C | 1 mm | 67% | 1.9 m/s | 5.1 |
| 2007 | 22.8°C | 17.7°C | 12.6°C | 29.9°C | 10.6°C | 5 mm | 71% | 2.1 m/s | 5.2 |
| 2006 | 23.4°C | 17.6°C | 11.9°C | 30.6°C | 9.8°C | 1 mm | 70% | 2.1 m/s | 4.7 |
| 2005 | 22.1°C | 16.7°C | 11.2°C | 30.7°C | 9.7°C | 2 mm | 73% | 2 m/s | 4.8 |
| 2004 | 25.1°C | 19.2°C | 13.3°C | 33.1°C | 9.5°C | 3 mm | 63% | 2.1 m/s | 5.7 |
| 2003 | 25.1°C | 19.3°C | 13.5°C | 34.3°C | 11.2°C | 1 mm | 67% | 2 m/s | 5.1 |
| 2002 | 23.7°C | 18.1°C | 12.4°C | 31.6°C | 10.1°C | 0 mm | 67% | 2 m/s | 5.3 |
| 2001 | 22.7°C | 17.2°C | 11.7°C | 32.7°C | 10.2°C | 7 mm | 75% | 1.9 m/s | 4.7 |
| 2000 | 24.8°C | 19.0°C | 13.1°C | 34.5°C | 10.7°C | 22 mm | 68% | 1.8 m/s | 5.2 |
| 1999 | 23.5°C | 17.8°C | 12.0°C | 31.6°C | 10.0°C | 3 mm | 69% | 1.8 m/s | 4.6 |
| 1998 | 23.1°C | 18.1°C | 13.1°C | 30.7°C | 10.8°C | 8 mm | 74% | 2 m/s | 4.9 |
| 1997 | 25.7°C | 20.1°C | 14.5°C | 33.2°C | 12.0°C | 4 mm | 67% | 2.1 m/s | 5.9 |
| 1996 | 23.1°C | 17.5°C | 11.9°C | 27.2°C | 10.4°C | 3 mm | 69% | 2 m/s | 4.9 |
| 1995 | 23.5°C | 17.9°C | 12.3°C | 30.6°C | 10.9°C | 1 mm | 74% | 2.1 m/s | 5.1 |
| 1994 | 24.3°C | 18.5°C | 12.7°C | 31.2°C | 10.7°C | 2 mm | 71% | 1.9 m/s | 4.8 |
| 1993 | 24.6°C | 18.5°C | 12.4°C | 31.3°C | 9.3°C | 2 mm | 65% | 2 m/s | 4.9 |
| 1992 | 24.5°C | 18.6°C | 12.8°C | 30.7°C | 9.9°C | 2 mm | 67% | 1.9 m/s | 5.1 |
| 1991 | 24.3°C | 18.3°C | 12.3°C | 31.4°C | 10.7°C | 1 mm | 71% | 1.7 m/s | 4.1 |
| 1990 | 25.3°C | 19.2°C | 13.1°C | 32.0°C | 11.5°C | 4 mm | 70% | 2 m/s | 5.4 |
| 1989 🌧️ | 22.8°C | 17.3°C | 11.8°C | 29.5°C | 10.4°C | 47 mm | 74% | 1.9 m/s | 4.7 |
| 1988 | 24.9°C | 18.3°C | 11.7°C | 34.1°C | 9.8°C | 0 mm | 61% | 2 m/s | 4.7 |
| 1987 | 24.9°C | 18.7°C | 12.5°C | 29.7°C | 10.9°C | 0 mm | 66% | 2.2 m/s | 4.5 |
| 1986 ❄️ | 21.1°C | 16.1°C | 11.2°C | 26.9°C | 10.0°C | 32 mm | 75% | 2.2 m/s | 4.9 |
| 1985 | 22.6°C | 17.3°C | 11.9°C | 30.1°C | 9.2°C | 16 mm | 71% | 1.9 m/s | 4.9 |
| 1984 | 26.6°C | 20.3°C | 14.1°C | 33.2°C | 10.9°C | 4 mm | 55% | 2 m/s | 5.6 |
| 1983 | 25.2°C | 19.6°C | 13.9°C | 33.0°C | 11.6°C | 19 mm | 70% | 1.9 m/s | — |
| 1982 | 23.4°C | 17.8°C | 12.3°C | 30.6°C | 10.0°C | 27 mm | 67% | 2.1 m/s | — |
| 1981 | 23.9°C | 18.0°C | 12.2°C | 31.0°C | 10.5°C | 9 mm | 69% | 2.2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 24.1°C with lows near 12.9°C (mean 18.5°C), based on 45 years of NASA POWER data.
September averages 7 mm of rainfall in San Francisco, one of the drier months. The wettest on record was 47 mm in 1989.
The hottest September reached 39°C in 2020. The coldest dipped to 9.2°C in 1985.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 0.3°C — but days and nights have moved in opposite directions. Overnight lows rose from 12.9°C to 13.7°C while daytime highs eased from 24.3°C to 24.2°C, narrowing the gap between day and night.
September is one of the warmer months of the year in San Francisco and one of the drier months, so plan for around 24.1°C daytime highs and 12.9°C at night.
Not quite — September is the 12th coolest month in San Francisco, averaging 18.5°C.
For September in San Francisco, pack light layers you can adjust through the day, with typical highs of 24.1°C and lows of 12.9°C.
Relative humidity in September averages 70% — moderately humid.
Average wind speed in September is 2 m/s. The windiest September on record averaged 2.5 m/s (2019).
The wettest September on record was 1989 with 47 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 San Francisco 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.
