Sun hours San Diego weather and climate for further months San Diego in January San Diego in February San Diego in March San Diego in April San Diego in May San Diego in June San Diego in July. 26 juin 2019 · You can get a look at average high and low temperatures, rainfall and hours of sunshine in the San Diego weather and climate guide. For beach days, water temperatures stay near summer highs when fall begins, hovering a little below 70°F through September, but they drop sharply in October.