L.A.’s summer heat arrives late

Summer, which seemingly fled Los Angeles this year, will make a brief cameo this week.

Forecasters say a high-pressure system moving in from Arizona and New Mexico will boost temperatures to between 90 and 104 degrees in the San Gabriel and San Fernando valleys, making for a heat wave that is to begin on Sunday and peak on Monday.

One of the Southland’s perennial hot spots, Woodland Hills, could reach the triple digits, and Pasadena may hit the mid-90s early this week.

“The summer heat has finally arrived,” said Bonnie Bartling, a weather specialist at the National Weather Service office in Oxnard. This is expected to be only the second time this summer that temperatures will top 100 in the valleys.

The heat will raise wildfire concerns in the mountains and Antelope Valley as humidity drops, the weather service said.

Anyone seeking relief may want to head closer to the beach, which will be protected from the heat by the marine layer, the low, cool clouds that hug the coast in the evenings and mornings. Downtown L.A. will hit the 80s through Tuesday, while highs at the beaches will stay in the 70s.

The heat wave is expected to be short-lived. Cooling is expected predicted to begin on Tuesday, but that day will also bring humidity from the south, so “it might feel sticky,” Bartling said.

Last week, the National Weather Service issued a statement explaining why summer jilted Southern California so far this year, saying persistent low-pressure systems have been loitering off the California coast for the last 2-1/2 months.

The phenomenon has kept Southern California’s traditional May gray and June gloom around for July and August. For much of this time, fog has rolled in overnight and made L.A.’s summer seem almost as chilly as those in San Francisco. The average temperature recorded at Los Angeles International Airport throughout July was 65.7, a low that matched records set in 1948 and 1965.

Lower-than-normal ocean temperatures have also kept onshore Pacific breezes “extra chilly,” according to the National Weather Service.

Those lower-than-normal ocean temperatures, a phenomenon scientists call La Niña, could exacerbate wildfire conditions this fall and winter by bringing little or no rain.

“The fires that would start would spread much easier during times of less precipitation, because the vegetation is much drier,” said Jamie Moker, a National Weather Service meteorologist in San Diego.

Southern California’s cool summer comes as much of the world has baked. The global average land surface temperature worldwide in July was the warmest on record, according to the National Oceanic and Atmospheric Administration. The agency has records going back to 1880.

Moscow, which has been suffering a heavy death toll from an extended heat wave and nearby fires that have raged out of control, set a record July 30 when the mercury hit 102, surpassing the previous record of 99 set four days earlier.

China had its warmest July since 1961, and Finland set a new all-time high of 99 degrees on July 29, breaking the previous record of 96.7 made in July 1914.

ron.lin@latimes.com