San Francisco Weather in September

September is the hottest month for San Francisco, California. Still, most days have pleasant temperatures with only a few days heating up to over 80 degrees Fahrenheit (27 degrees Celsius). Along with little rain and plenty of sun, September brings some of the best weather of the year to San Francisco.

This page gives detailed information on the typical September temperature, precipitation, sun, humidity, wind and storms for San Francisco. The temperature, rainfall, sunshine and wind speed numbers here are historical averages based on climate data gathered in downtown San Francisco near the corner of Buchanan and Hermann Streets. The other measurements are averages at San Francisco International Airport, located south of the city center.

Temperature Weather iconTemperature

70 °F September average high 21 °C
56 °F September average low 13 °C

September is San Francisco's hottest month overall, with temperatures peaking from the 21st to 28th when daily highs average 71 °F (22 °C). The nights then have an average low of 56 °F (13 °C).

14 days 70 °F max. or more (21 °C)
28 days 60 °F min. or less (16 °C)

Usually every day in September warms to over 60 °F (16 °C) in San Francisco. The city averages 5 days this month when the thermometer reaches into the 80s °F (over 27 °C). Temperatures above 90 °F (32 °C) can occur during September, yet it doesn't get that hot every year.

Usually the thermometer dips below 60 °F (16 °C) almost every night this month. But September does not normally get as cold as 40 °F (4 °C).

Rainy Weather iconRain

0.1 in total precipitation 3 mm
1 day of rain

Every few years, San Francisco receives no rain in September. About one in four years, September receives 0.1 inches (3 mm) or more of rain.

Sunny Weather iconSun

72 % sunshine
18 days clear skies

The sun's rays reach the ground in San Francisco during 72 percent of daylight hours on average in September, for a total of 268 hours in the month. Typically on 18 days this month the sky is mainly clear, with at most 30 percent cloud cover.

Sunlight in September at San Francisco lasts for 12 hours and 23 minutes a day on average. The longest day of the month is the 1st with 12 hours and 58 minutes of daylight. By the end of the month, the days have shortened to 11:49 from sunrise to sunset. These durations can vary by a minute or two from year to year.

Humid Weather iconHumidity

72 % September average humidity

The relative humidity in San Francisco during September usually peaks at 83 percent in the morning then drops to 53 percent by early afternoon.

Local Time1 am4 am7 am10 am1 pm4 pm7 pm10 pm
Humidity % 82 83 82 65 53 58 73 78

Windy Weather iconWind

9.1 mph September wind speed average 14.6 kph

September is a little windier than most other months in San Francisco.

Stormy Weather iconStorms

0 days rainfall of 0.5 inches (13 mm) or more
0 days with thunderstorms in September

About once a decade, San Francisco receives as much as an inch (25 mm) of rain in one day during September. Every few years a thunderstorm shows up at San Francisco in September.


The weather data here are long-term averages provided by the US National Centers for Environmental Information (NCEI). Temperature and precipitation are 1991-2020 normals while humidity and thunderstorms are 1961-1990 normals.

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