How Long Will this Humid Heat Wave Last?

Temperatures and humidity levels will rise to uncomfortable levels in the Southland today at the start of a heat wave expected to last until early next week, and perilous conditions characterized by strong rip currents and high surf will prevail along the coast until tonight, National Weather Service forecasters said.

“The combination of high pressure aloft and weak offshore flow will bring very hot weather to much of Southwestern California ...” warned an NWS statement, asserting that “slight cooling” is expected Friday and Saturday, although temperatures will not be returning to normal until early next week..

“The prolonged heat wave will bring a risk of heat-related illness through much of the week. Those at highest risk include children, the elderly, and pets without adequate shelter,” warned the statement, which noted that the heat would heighten electricity use throughout the region, “increasing the threat of power outages.”

The NWS forecast highs today in the mid 90s in metropolitan Los Angeles and the low 100s in the San Gabriel, San Fernando, Santa Clarita and Antelope valleys as well as inland Orange County.

Temperatures today and during the rest of the heat wave will be running 10-15 degrees higher than normal, said NWS meteorologist Kathy Hoxsie. The high heat is being attributed to high pressure developing over the region, combined with the fact that only weak winds are blowing in from the ocean.

Also afflicting the region today is high humidity, which is forecast to be at the 50 percent level in the coastal plains -- the norm is 20-30 percent -- and around 40 percent in valley areas, compared to the teens, which would be normal, Hoxsie said. The humidity is attributed to lingering moisture from Hurricane Linda.

The conditions prompted the NWS to issue an excessive heat warning for the San Gabriel and Santa Monica mountains in both Los Angeles and Ventura counties, with highs of 105 expected at low elevations, and the San Fernando, San Gabriel and Santa Clarita valleys. It will be in force from 11 a.m. today until 8 p.m. Thursday.

Normally, excessive heat warnings are issued when humidity levels stand to make temperatures feel even hotter than they are, but in this instance the warning would have been issued in any event as a result of the high temperatures, Hoxsie said.

Forecasters said those at greatest risk of suffering heat-related ailments were infants, the elderly, the homeless, outdoor workers and people taking part in outdoor activities in the heat.

They urged residents to drink plenty of water; wear light-colored and lightweight clothing; stay out of the midday sun; check on neighbors and the elderly to make sure they are not being overwhelmed by the heat; and never, ever leave children, the elderly, or pets in a vehicle parked in hot weather.

The NWS forecast sunny skies today and highs of 81 in San Clemente; 82 in Avalon;  85 in Newport Beach and Laguna Beach; 86 at LAX; 92 on Mount Wilson; 97 in Irvine, Anaheim, Long Beach and downtown L.A.; 98 in Mission Viejo and San Gabriel; 99 in Fullerton; 100 in Yorba Linda, Palmdale and Burbank; 101 in Lancaster; 102 in Pasadena and Saugus; and 105 in Woodland Hills. Temperatures will be a couple of degrees higher in several communities on Wednesday and start a cooling trend on Friday. By Monday, many communities that will have withstood temperatures in the 90s and above will be back in the 80s.

Along the coast, high surf is expected through tonight as a result of a long-period swell in the Pacific, said the NWS, adding that the highest surf -- 3 to 6 feet, with 7-foot sets -- will pound south- and southwest-facing beaches.

“Strong, frequent rip currents will continue to be a significant hazard,” an NWS statement said.

Anyone who plans to swim in the ocean today should do so near a lifeguard, the NWS urged, adding that beachgoers must avoid climbing on rocks or jetties because of the risk of being scooped up by “sneaker waves.”

City News Service