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 °F (27 °C). 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 rest of the measurements are averages at the San Francisco International Airport, located south of the city center.

Temperature Weather iconTemperature

70 °F September average high 21 °C
55 °F September average low 13 °C

In most years, San Francisco averages a daily maximum temperature for September that's between 67 and 73 degrees Fahrenheit (20 to 23 degrees Celsius). The minimum temperature usually falls between 54 and 57 °F (12 to 14 °C).

September is San Francisco's hottest month overall, with daytime temperature peaking from the 19th to 29th at 70.4 °F (21.3 °C). The warmest nights run from late August through early September when the low averages 55.3 °F (12.9 °C).

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

Nearly every day in September warms to over 60 °F (16 °C) in San Francisco. The city averages 4 days this month when the thermometer reaches into the 80s °F (over 27 °C). Temperatures above 90 °F (32 °C) are most likely to occur during September, yet it doesn't get that hot every year.

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

Rainy Weather iconRain

0.2 in total precipitation 5 mm
2 days of rain

Every few years, San Francisco receives no rain in September. The rainiest Septembers get at least 0.2 inches (6 mm).

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.

Reference

These weather data are long-term historical averages provided by the National Climatic Data Center of the United States. The temperature and precipitation numbers are 1981-2010 normals while the humidity and thunderstorm statistics are 1961-1990 normals.

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