Weather is probably a major factor when you plan your trip to San Sebastian, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually April and May, with an average temperature of 24°C, while the coldest months are January and December, with an average of 20°C. The rainiest months in San Sebastian are September, June, August and October, with each month seeing an average of 331 mm of rainfall.