A National Weather Service Heat Advisory takes effect across the Lamorinda area Saturday, Oct. 3, at 11 a.m., with inland parts of the Bay Area forecast to reach the mid-90s to as high as 103 degrees.

The advisory runs through 10 p.m. Monday, Oct. 5, covering the East Bay hills and interior valleys. The NWS issued the advisory Thursday, Oct. 1, at 9:43 a.m.

Daytime highs across the advisory zone are forecast in the mid-90s to near 103, according to the NWS Bay Area forecast office. Overnight lows will stay in the upper 60s to mid-70s at higher elevations. That limits the body's ability to recover from daytime heat.

The San Francisco Chronicle reported that Saturday night will be warmer in the Oakland and Berkeley hills and the Diablo Valley, with overnight lows in the low to mid-60s.

The NWS said prolonged outdoor exposure, especially with physical exertion, raises the risk of heat-related illness for anyone without adequate cooling or hydration.

Who is most at risk

Older adults face the greatest danger. Adults 65 and older are at higher risk because their bodies do not adjust as well to rapid temperature changes, according to Contra Costa Health. The department also noted that electric fans do not protect against heat illness once temperatures reach the 90s.

KQED reported that fire risk will also be elevated during the heat event, though meteorologists do not expect high winds that could worsen fire spread.

How to stay safe

The NWS advises residents to drink plenty of water or sports drinks, shift outdoor activities to cooler parts of the day, take frequent breaks in air-conditioned spaces or shade, and never leave people or pets in unattended vehicles.

Contra Costa County residents who need help reaching a cool location can call 211 or Mobility Matters at (925) 284-2207 for transportation assistance. County Connection bus service is also available at 925-676-7500. Residents without housing can call 211 and ask for a CORE outreach team to access air-conditioned facilities, according to the county's heat safety page.

The county also urges residents to sign up for emergency alerts through the Contra Costa County Community Warning System. The NWS updates its Bay Area forecasts daily through its forecast office page.

The advisory expires at 10 p.m. Monday, Oct. 5.