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.
|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).
|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.
|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.
|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 Time||1 am||4 am||7 am||10 am||1 pm||4 pm||7 pm||10 pm|
|9.1 mph||September wind speed average||14.6 kph|
September is a little windier than most other months in San Francisco.
|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.