The hottest month in San Francisco is September when the average maximum temperature is 23°, average temperature is 18° and average minimum temperature is 13°.
The coolest month in San Francisco is January when the average maximum temperature is 14°, average temperature is 10° and average minimum temperature is 6°.
The longest days in San Francisco are in June, with an average of 14.8 hours of daylight per day. December has the shortest days with an average of 9.6 hours of daylight per day.
The sunniest days in San Francisco are in June which has the most hours of sunshine per day with an average of 11.2 hours of sunshine per day, making it a very sunny and pleasant month with long bright days. December has the least sunshine with an average of 5.1 hours of sunshine per day, making it a sunny month that is overcast at times.
The ultraviolet index is the highest in July when it reaches 10.6 and lowest in December when it reaches 2.2.
An ultraviolet index reading of 8 to 10 indicates a very high risk of harm from unprotected sun exposure. Unprotected skin risks burning in less than 15 minutes. Take extra precautions because unprotected skin and eyes will be damaged and can burn quickly. Tanning will be safest before 10am and after 4pm but only with a good application of sun screen. For those with sensitive skin stay in the shade and wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days. Watch out for relections from water that may increase ultraviolet exposure.
The warmest sea water temperatures in San Francisco are found in September when they peak at 20° and lowest in February when they dip to 15°.
The sea is best for swimming between May and December when the temperature is above 17° which is cool for swimming, shorty wetsuit may help you extend your time in the water.
The wettest month in San Francisco is December with 37.1cm of rain and February has the most days of rain with 12.7 days with some rain, a slightly wet time to visit the beach.
The driest month in San Francisco is July with 0cm of rain and the least days of rain with 0.3 days with some rain, an extremely dry time to visit the beach.
The most humid month in San Francisco is September with a dew point (an indicator of humidity) of 14° which is comfortable for everyone.
The least humid month in San Francisco is January with a dew point of 8° which is a bit dry for some.
The most windy month in San Francisco is May when the average maximum windspeed is 41kmh and the average wind speed is 20kmh.
The least windy month in San Francisco is January when the average maximum windspeed is 26kmh and the average wind speed is 9kmh.