The hottest month in San Diego County is September when the average maximum temperature is 26°, average temperature is 21° and average minimum temperature is 17°.
The coolest month in San Diego County is January when the average maximum temperature is 19°, average temperature is 13° and average minimum temperature is 8°.
The longest days in San Diego County are in June, with an average of 14.3 hours of daylight per day. December has the shortest days with an average of 10 hours of daylight per day.
The sunniest days in San Diego County are in July which has the most hours of sunshine per day with an average of 10.2 hours of sunshine per day, making it a very sunny and pleasant month with long bright days. January has the least sunshine with an average of 7.2 hours of sunshine per day, making it a quite sunny month with some cloud cover.
The ultraviolet index is the highest in July when it reaches 11.9 and lowest in December when it reaches 3.5.
An ultraviolet index reading above 11 indicates an extreme risk of harm from unprotected sun exposure. Unprotected skin risks burning in less than 10 minutes. Take all precautions because unprotected skin and eyes can burn in minutes. 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 Diego County are found in August when they peak at 29° and lowest in January when they dip to 17°.
The sea is best for swimming between May and December when the temperature is above 23° which is warm and pleasant for relaxing and swimming for long periods.
The wettest month in San Diego County is February with 16cm of rain and the most days of rain with 11.2 days with some rain, a slightly wet time to visit the beach.
The driest month in San Diego County is June with 0.1cm of rain and August has the fewest days of rain with 0.8 days with some rain, an extremely dry time to visit the beach.
The most humid month in San Diego County is August with a dew point (an indicator of humidity) of 17° which is OK for most but slightly uncomfortable for some.
The least humid month in San Diego County is January with a dew point of 8° which is a bit dry for some.
The most windy month in San Diego County is April when the average maximum windspeed is 21kmh and the average wind speed is 8kmh.
The least windy month in San Diego County is November when the average maximum windspeed is 18kmh and the average wind speed is 7kmh.