Triple-digit temperatures will heat up many parts of Southern California this weekend, posing a high risk for heat-related illnesses, forecasters said Saturday.

In the valley and inland areas, temperatures are expected to be significantly above normal through Monday before a brief cooldown arrives.

An extreme heat warning — the highest level of heat alert issued by the National Weather Service (NWS) — is in effect for parts of San Bernardino and Riverside counties, while most of Southern California, from Ventura County to San Diego County, remains under a heat advisory.

Inland coastal areas, including downtown Los Angeles, are also under a heat advisory through Monday, with daytime highs potentially reaching 96 degrees, according to the NWS.

A brief cooldown on the way

Forecasters said daytime highs could range from 97 to 107 degrees.

“Hour by hour, you want to get out early and get things done (by) 9 a.m.,” NBCLA meteorologist Shanna Mendiola said. “Between 9 a.m. and 11 a.m., there’s a big jump about 10 degrees.”

Mendiola urged people to limit outdoor activities during the heat wave and stay in air-conditioned rooms if possible.

“Drink plenty of water, not that soda or sugar that could weigh you down,” the meteorologist said, recommending people wear loose, light-colored clothing when outside.

People without access to air conditioning were encouraged to seek relief at public libraries, recreation facilities, senior centers or other public buildings. See LA County cooling centers here. Orange, Riverside, San Bernardino and Ventura counties are also offering cooling centers.

Forecasters noted the weather system will also keep temperatures elevated in many areas at night, when people normally get some relief from the heat.

“The combination of above normal daytime highs and overnight lows along with the higher humidities will create a dangerous environment as people’s bodies (those without air conditioning) will be heat stressed day and night with no real recovery period,” according to the NWS. “For all of these reasons heat advisories are in effect through Monday evening.”

The heat wave is expected to continue into early next week with a “short little reprieve,” Mendiola said.

“There is a little bit of relief, but not by much,” she explained, saying there will be a slight dip in temperatures after Monday before heat picks up again on Thursday.

Warning at beaches

Officials warned people who are hoping to cool down at Southern California beaches should look out for dangerous surf and rip current conditions.

A beach hazards statement was in effected through Sunday evening, largely due to elevated surf and dangerous currents along the coast.

Beachgoers were urged to swim near a lifeguard. If they get caught in a rip current, they should not swim directly back to the shore against it. Rather, people should swim parallel to the shoreline until being out of the current.

In LA County, health officials urged people to enter the water at four beaches because of high bacteria levels.

The Los Angeles County Department of Public Health issued ocean water use warnings for the following locations:
   — Mother’s Beach in Marina del Rey, entire swim area
   — Inner Cabrillo Beach in San Pedro, entire swim area
   — Topanga Canyon Beach in Malibu, 100 yards up and down the coast from the lagoon
   — Santa Monica Pier, 100 yards up and down the coast from the pier.