SACRAMENTO, Calif. -- Gov. Arnold Schwarzenegger is urging Californians to prepare for sizzling hot weather this weekend, which could lead to dehydration and heat exhaustion.

Sacramento temperatures on Friday are expected to tip 100 degrees, while weekend temperatures will stay in the high 90s.

The Office of Emergency Services, the California Department of Public Health and numerous other state agencies to prepare for extreme high temperatures, the governor's office said.

"Today is the first official day of summer and the hot temperatures are already upon us. We stand ready to mobilize whatever additional resources are necessary to ensure local officials get the help and support they need in protecting their residents from the severe heat," OES Director Henry Renteria said.

Forecasters are predicting 103-degree heat and the possibility of dry thunderstorms in the Ventana Wilderness of the Los Padres National Forest.

The San Fernando Valley city of Van Nuys began frying early, hitting 94 degrees by 9 a.m., according to the National Weather Service. A high pressure system spread hot air from the desert -- which saw highs of 118 in Thermal and 116 in Palm Springs on Thursday -- to the Los Angeles area.

"Summer heat waves can be extremely dangerous. Everyone should be on alert-it's important to pay attention to signs of heat-related illness, and especially to monitor infants, young children, seniors and people with underlying health problems," CDPH Director Mark Horton said.

Officials offered the following tips to stay healthy during high heat:

• Drink plenty of water, especially when taking medication.
• Wear lightweight and light-colored clothing.
• Avoid physical activities during periods of peak temperatures.
• Check on neighbors and family members to ensure they are not being harmed by the heat.
• Watch for signs of heat-related illness, including fatigue, nausea, headache and vomiting.
• Visit malls, theaters and other public places that are air-conditioned if you don't have your own air conditioning.