S.D. Sizzles in 100-Degree Indian Summer

Unseasonably high temperatures warmed Southern California Sunday, topping 100 degrees in some areas of San Diego County and creating a pleasant Indian summer effect.

Borrego Springs sizzled at 105 degrees, and Fallbrook reported a high of 100. Elsewhere in the county, most inland valleys reported highs in the 90s, while the beaches stayed cooler with temperatures in the upper 70s and low 80s.

Downtown San Diego reached 84 degrees, which is 9 degrees above normal for this time of year, according to meteorologist Harvey Hastrup of the National Weather Service.

“We have a weak Santa Ana condition with light north-easterly winds, which is bringing very warm air into the county,” Hastrup said. “There will be a tad bit of cooling tomorrow and a lot more cooling on Tuesday, so we saw the best over the weekend,” he said.

Temperatures Monday are expected to drop a few degrees, hitting 80 downtown and 88-96 degrees in inland areas. Tuesday will be considerably cooler and should bring the return of the usual pattern of night and morning low clouds followed by hazy afternoon sunshine, the forecasters predict.

Temperatures in the inland valleys hovered in the 90s Sunday, with reported highs of 98 in Santee, 96 in Escondido, 95 in El Cajon and 93 in La Mesa and Lemon Grove.

While San Diegans enjoyed the warm weather, Los Angeles residents sweltered in temperatures that soared up to 102 degrees. It was the hottest Oct. 9 on record in Los Angeles, sending people to the beaches there in double the usual October numbers.

Hot, bone-dry Santa Ana winds under cloudless skies sent the temperature to 102 degrees at the Los Angeles Civic Center by 2 p.m., beating the previous record of 98, which was set in 1976. The normal high for the date is 80 degrees.

Weather forecasters say the unseasonal heat will continue today in Los Angeles.

“You guys are sizzling,” said meteorologist Janice Roth of WeatherData Inc., which provides forecasts for The Times.

But as hot as it was, Sunday’s peak was still several degrees cooler than last Sept. 4, when the scorching 110-degree reading equaled the hottest day ever in Los Angeles. The previous high this October was 89, which was reached Saturday.

Relative humidity ranged from 51% to 16%.

The hot, dry weather, which meteorologists termed a “mild Santa Ana condition,” stems from the influence of a high-pressure system sitting over northwest Washington that is causing a vast, clockwise rotation of winds over the western United States, according to Roth.

The slowly wheeling weather system causes hot dry winds to blow from Nevada into Southern California. In addition to the desert heat that the northeasterly winds bring, they have been preventing the formation of low clouds, which usually shield the area from direct sunlight for part of the day.

And the winds have also been heating up through compression as they flow over the San Gabriel Mountains and drop in altitude to sea level.