The National Weather Service issued an excessive heat warning Saturday through 9 p.m. for San Diego County deserts.
High temperatures in the western valleys were expected to be 92-97 degrees and in the foothills 102-107, the NWS said.
But along the coast, ocean breezes will prevail, forecasters said, with highs 75-80 and overnight lows 60-65.
And in the inland valleys, highs will be 86-91 with overnight lows 61-68.
"Cooling will progress slowly inland beginning on Sunday as the high aloft weakens and the marine layer slowly deepens,'' the weather service said. "Westerly winds will increase early next week over the mountains and deserts as well, becoming quite gusty through and below passes."
Low clouds and some fog will return to coastal areas each night and morning, spreading farther inland next week, forecasters said.
"The southerly surge of fog has already shrouded southwest San Diego County Saturday morning and will be touching most of the county's coast at times today," the weather service said. "No real change later next week as the weak West Coast trough keeps the flow aloft dry from the southwest and temps near to slightly below normal."