Heat wave strikes SoCal on Tuesday, temperatures expected to reach triple digits

High heat generated by a strong ridge of high pressure will afflict much of the Southland on Tuesday, creating a somewhat elevated fire risk, the National Weather Service warned.

A heat advisory, which warns of hot temperatures able to cause heat- related illnesses, will be in effect in the San Fernando, San Gabriel and Santa Clarita valleys, the Santa Monica Mountains Recreational area, the L.A. County Coast, beach cities and metropolitan Los Angeles from 10 a.m. to 9 p.m. Tuesday, when temperatures will be in the upper 90s to around 104 -- hotter than usual for this time of the year, according to the NWS.

But no advisory was issued for the San Gabriel Mountains, where temperatures are expected to be only in the 80s, according to forecasters. No special advisory was issued for the Antelope Valley, either; highs in that valley may reach 104, but that's not uncommon as summer approaches.

The heat advisory will extend as far east as Pomona.

Overnight low temperatures will be in the mid 60s to near 70 degrees.

"There is an increased risk of heat-related illnesses,'' warned an NWS statement. "The most vulnerable include those involved with outdoor activities, those without access to air conditioning, young children, and the elderly. Temperatures inside vehicles, even if the windows are partially open, can quickly rise to life-threatening levels.''

The NWS warned on its website that low humidity is expected, creating elevated fire danger. NWS meteorologist Kristen Stewart added that humidity levels will be in the teens away from the coast. But she said that, even with the dryness, the situation does not call for the issuance of red flag warnings because of the absence of strong winds and the fact the vegetation remains moist because of the extensive rain earlier this year.

The hot spell is likely to start dissipating Wednesday as the ridge of high pressure begins breaking down and the marine layer deepen, Stewart said.

The NWS forecast partly cloudy skies in L-A County Tuesday and highs of 78 degrees in Avalon; 79 at LAX; 87 on Mount Wilson; 92 in Long Beach; 93 in Downtown L.A.; 100 in San Gabriel; 101 in Burbank and Lancaster; 102 in Pasadena, Saugus and Palmdale; and 103 in Woodland Hills. Temperatures will be 10 degrees lower Wednesday in several communities and up to 19 degrees lower by next Monday at the end of an extended NWS forecast.

Sunny skies were forecast Tuesday in Orange County, along with highs of 72 in San Clemente; 73 in Newport Beach; 75 in Laguna Beach; 90 in Irvine and Fullerton; 93 in Mission Viejo, on Santiago Peak and on Ortega Highway at 2,600 feet; 98 in Yorba Linda; 99 in Fremont Canyon and Trabuco Canyon. Wednesday's highs will be up to 10 degrees lower and more than 20 degrees lower in some communities by Monday.

CNS contributed to this report.