Prolonged exposure to high temperatures increases the risk of getting a heat-related illness.
In most areas, the warning goes into effect at 10 a.m. Sunday and will remain in effect through 10 p.m. Wednesday.
Summer has chose to go out on a hot streak in the Bay Area, as the National Weather Service (NWS) continued an Excessive-Heat Warning for much of the region Monday, warning of triple-digit temperatures that put the "entire population at risk" in parts of the East Bay and South Bay.
The high today for Fallbrook is expected to hit 89 degrees, but by Tuesday, highs are predicted to hit triple digits.
The Antelope Valley and other inland valleys are expected to face the worst heat this week, with triple-digit temperatures. Chula Vista is forecast to reach 95 degrees, one degree above the record for the date and 20 degrees above average, while Ramona is forecast to hit 108 degrees, besting the previous August 29 high of 105.
The smoke and stale air over the Bay Area also triggered a third consecutive Spare The Air day warning for the region.
Daytime highs will range 100 to 110 degrees with overnight lows in mainly in the upper 60s to mid 70s with some of the warmer foothill locations only cooling off into the lower 80s.
The National Weather Service warns beachgoers to beware.
A grueling, scorching heat wave is expected to grip the county at least throughout the week, with highs of 108 and 107 expected Monday and Tuesday, respectively.
The National Weather Service said the heat poses a "dangerous situation" and urged residents to take precautions.