Downtown Los Angeles was 89 degrees (31.6 Celsius) at noon Monday and other locations were into the 90s, well above seasonal normals.
The temperatures were due to high pressure and gusty offshore flow.
The Central Coast and parts of the San Francisco Bay Area were expected to get into the 80s.
Northern portions of the Bay Area will see light rainfall Tuesday as a weak weather system moves through, followed Wednesday by a slightly stronger system with more widespread light rain that could last into Thursday.
The National Weather Service said the heat would be brief, as sea breezes return Tuesday.