Weather is probably a major factor when you plan your trip to San Gabriel, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually October and November with an average temp of 53°F, while the coldest months are August and July with an average of 52°F. The rainiest months in San Gabriel are November, December, April, and March, with each month seeing an average of 14 inches of rainfall.