Temperatures will rise starting Friday and continue through this weekend in the Bay Area, according to the National Weather Service.
NWS officials said the hottest days will be Saturday and Sunday, with temperatures rising as many as 10 to 15 degrees above the seasonal normal. The warmest areas in the region will be inland where temperatures may reach 100 degrees, weather service officials said.
The forecast for Saturday says afternoon temperatures will reach 94 in Portola Valley, 93 in Woodside, 88 in Menlo Park and 86 in Atherton.
Regionally, the weather service says it should be 100 degrees in both Concord and Fairfield. The afternoon high Saturday for Livermore and Cloverdale is forecast to be 97 degrees, according to the weather service.
Forecasters said they expect San Rafael to reach 90 degrees Saturday. The Saturday forecast for coastal locations is between 70 and 80 degrees, NWS officials said.
Bay Area locations will cool off by Monday, forecasters said.
Weather service officials said the heat poses the greatest threat to the young, elderly, people working and exercising outside and ill people sensitive to the heat.
The warm weather also increases the risk of wildfires as brush and grass dry out, according to the NWS.