San Francisco will be about 75 to 80 degrees, five to 10 degrees hotter than usual, said National Weather Service forecaster Steve Anderson.
Temperatures will be similarly above average in the East Bay, where it will reach the 90s, while the South Bay will be in the 70s and 80s, Anderson said.
Health officials advise people to have water on hand and to keep children and pets in areas with ample shade during the heat wave.
Bay Area temperatures will then cool slightly over the weekend, with a chance of rain coming on Tuesday, Anderson said.
"It will be the first bona fide storm of the season, the first cold front," he said.
Don't put away the shorts and sandals just yet though -- Anderson said warm weather will likely return to the region and last all the way into November.
