A heat wave is about to wash over the Southland and send temperatures into triple-digit territory amid an elevated danger of wildfire, the National Weather Service said Tuesday, issuing an excessive heat watch from Friday morning through Saturday evening.
The heat watch will be in effect along the Central Coast, in Ventura County, in Orange County and in all of L.A. County, including beach cities, metropolitan L.A., the Downtown area and the Hollywood Hills, all valley areas, and both the San Gabriel and Santa Monica mountains.
While the watch is in force, highs are expected to reach 102 degrees along the coast, 106 in the mountains, 107 in inland Orange County, and 112 in L.A. County valleys, according to the NWS.
The weather service stressed in a statement that the type of temperatures expected create an “increased potential for heat-related illnesses.”
“Take extra precautions if you work or spend time outside,” it urged. “When possible, reschedule strenuous activities to early morning or evening. Know the signs and symptoms of heat exhaustion and heat stroke. Wear lightweight and loose-fitting clothing when possible and drink plenty of water.”
Especially important is to “never, ever, leave people or pets in enclosed vehicles, even for a short period of time. Temperatures inside vehicles, even if the windows are partially open, can quickly rise to life-threatening levels.”
The NWS attributed the forthcoming heat wave to “a strong upper level high pressure system is forecast to expand westward from the Central United States later this week, causing heat to build significantly across Southwestern California.”
In the meantime, a wind advisory has been issued for the Antelope Valley and is scheduled to expire at 9 Tuesday evening. Until then, winds of 20-30 miles per hour will buffet the region, accompanied by 45-mph gusts, although 55-mph gusts are possible in the foothills.
The NWS said a fairly deep marine layer and onshore flow will keep temperatures near or below normal across most of the region through Independence Day. But on Thursday, the atmosphere will begin to warm, the marine layer will become more shallow, and onshore flow will decrease.
“This will lead to noticeable warming on Thursday, especially inland, where high temperatures should approach 100 degrees in the Antelope Valley, in the mountains at lower elevations, in the interior valleys of San Luis Obispo County and in the Cuyama Valley. Temperatures could even get close to 100 degrees Thursday in some of the warmest locations in the Los Angeles and Ventura County valleys.”
Gusty north winds are expected to develop across southern Santa Barbara County and possibly through the Interstate 5 corridor Thursday night.
“… The combination of gusty winds, high temperatures and low relative humidity will increase fire danger substantially, possibly approaching critical levels,” according to a statement.
Also scheduled this week is a beach hazards statement from Wednesday evening through Friday evening in both L.A. and Orange counties.
“A large southerly swell from Hurricane Fabio will move into the waters late Wednesday evening, peak in height Thursday afternoon through Friday morning, then slowly subsiding through Friday night,” according to an NWS statement. “This swell is slightly smaller but very similar to the swell from Hurricane Marie in August 2014, when large surf, lethal rip currents, and damaging coastal flooding … occurred over southwest California. The surf and rip currents will be especially dangerous considering the anticipated large beach crowds from the record hot temperatures.”
Surf of 8-11 feet is expected in L.A. County, 6-8 feet in Orange County.
Also expected are life-threatening rip currents, sneaker waves and coastal flooding, and the beach hazard statement could be replaced by a more serious high surf advisory.
Any swimmers who get ensnared in rip currents should swim parallel to shore until able to break free.
On Friday and Saturday, “the very high daytime temperatures and limited overnight cooling will create significant heat stress for people in the region,” the NWS warned. “People should plan to reduce time in the sun during peak heating hours later this week into this weekend and drink additional water to keep hydrated.”
The expected rise in temperatures will be dramatic. Downtown L.A. for example, will go from a high of 76 Tuesday to 100 on Friday, according to an extended NWS forecast. Pasadena, expected to reach 81 Tuesday, is forecast to have a high of 108 Friday, and Woodland Hills will go from 85 to 111.
A similar progression is expected in Orange County, although temperatures will be a little lower than in Los Angeles. Along the coast, San Clemente will go from 69 Tuesday to 87 Friday, but inland temperatures will climb more sharply. Yorba Linda, for instance, will be at 81 Tuesday but 107 Friday and 109 Saturday.