The official excessive heat warning is in effect from noon Sunday to 8 p.m. Tuesday.
Very hot temperatures can create a situation in which heat illnesses are possible.An Excessive Heat Warning means that a prolonged period of dangerously hot temperatures will occur. County officials also advised residents to stay in air conditioning during the hottest hours of the day, take cool showers, avoid using the oven to cook and avoid unnecessary sun exposure.
The heat wave will kick off Friday, with the mercury climbing into the upper 80s in San Jose and into the mid 90s in Morgan Hill, Pi said. A less severe heat advisory for mountain areas with elevations lower than 5,000 feet, which includes Julian and Pine Valley, will run from 11 a.m. Saturday to 9 p.m. Wednesday. In the Coachella Valley, highs are predicted to be 109 to 114 degrees today, 112 to 117 degrees Sunday, 114 to 119 degrees Monday, 117 to 122 degrees Tuesday and 115 to 120 degrees Wednesday.
The forecast for Friday calls for a high of 97 degrees at Travis Air Force Base, increasing to 99 Saturday and 103 Sunday before dipping below the century mark Monday to 98, according to the National Weather Service.
A ridge of high pressure centered over Southern California is to blame, said Will Pi, a meteorologist with the weather service.
Authorities also warned against leaving children or pets in parked cars, which can heat up to lethal levels in just minutes.
And with temperatures this high, records will be broken. Anyone overcome by heat should be moved to a cool and shaded location. "Extreme heat such as this is not just an inconvenience, it can be risky and even deadly, but we can protect ourselves, our families, and our neighbors if we take steps to remain cool and hydrated".