Weather is probably a major factor when you plan your trip to San Onofre, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually February and March, with an average temperature of 28°C, while the coldest months are November and December, with an average of 27°C. The rainiest months in San Onofre are October, August, September and June, with each month seeing an average of 257 mm of rainfall.