Weather will likely play an important role when you plan your trip to San Francisco, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually March and April, with an average temperature of 29°C, while the coldest months are December and November, with an average of 26°C. The rainiest months in San Francisco are October, September, June and May, with each month seeing an average of 432 mm of rainfall.