Southern California has seen some toasty Octobers, but this year’s start to the fall season has been marked by a persistent heat wave that’s shattered records and ushered in an unprecedented streak of 100-degree days.
The extreme heat is driven by a persistent high pressure ridge that has parked over the region causing sinking warming air with very little overnight relief. That is paired with down-sloping winds and uncharacteristically warm ocean temperatures — driven in part by an El Niño that has reduced Southern California’s sea breeze, frequently known as its natural air conditioning.
“We’re going on Day 4 of this really significant heat wave and we still have several more days of heat,” said Rose Schoenfeld, a meteorologist with the National Weather Service in Oxnard. “We do have heat events in October, but this streak of 100-plus days is definitely starting to become pretty notable.”
The average number of 100-degree days in downtown Los Angeles in a typical October has been closer to zero than one since the weather service began keeping records in the late 1800s. This month, downtown is on a four-day consecutive streak of temperatures 100 degrees or higher — the longest consecutive stretch in October since records began.
Downtown is currently tied for the most 100-degree-plus days in October with 1958 and 1971, but could surpass those years if the mercury hits 100 degrees Tuesday, according to the weather service.
“If we get another one tomorrow, then we would be at the most 100-degree-plus days in October in downtown L.A. ever,” Schoenfeld said.
The current heat wave already has broken daily heat records across the Southland.
Downtown Los Angeles broke a daily heat record Monday with the mercury reaching 104 degrees, shattering the previous record of 101 set in 1954 and tied in 1971.
The Burbank Airport hit 101 degrees Sunday, breaking the previous record of 100 set in 1964. Camarillo hit 99 degrees, inching past the previous record of 98 set in 1953. And Oxnard hit 99 degrees Sunday, shattering the daily record of 94 set in 2023.
In Orange County, Anaheim hit 101 degrees Sunday, blowing past the 98-degree record set in 2020.
San Diego hit 100 degrees, toppling a record of 97 set in 1987. The Oceanside Harbor registered 98 on Sunday, toppling the record of 97 set in 1953. And Ramona hit 101, just past the record of 100 set in 1987.
“It’s going to be pretty darn warm,” UCLA climate scientist Daniel Swain said of this week during a recent briefing on his Weather West channel.
Temperatures between 15 and 22 degrees above normal are expected to persist through Thursday. Highs along the coasts and valleys will be in the 90s up to the low 100s in the coming days. Even the beaches will provide little relief, with temperatures in the upper 80s.
The ocean is expected to bring its own dangers beginning Tuesday with elevated morning and evening tides and elevated surf as a result of Hurricane Rachel, located several hundred miles off the coast of Baja California with sustained winds of up to 85 mph.
The weather service is warning of dangerous rip currents and elevated surf of 3 to 6 feet on Catalina and Santa Barbara Islands as well as at Los Angeles and Ventura County beaches. The most susceptible areas will be Long Beach and the Avalon Harbor on Tuesday and Wednesday and then Malibu through Ventura County from Wednesday through Friday.
“Moderate flooding of sea water is a possibility over some vulnerable low-lying coastal areas, especially around the morning and evening high tides, including over beach parking lots, bike paths, and harbor walkways. Moderate beach erosion is possible to likely,” according to the weather service.
And those looking for relief won’t find it overnight.
It’ll still be warm after dark too, forecasters say, with the mercury dipping only into the upper 60s to mid-70s across much of the region. The weather service in Oxnard and San Diego issued extreme heat warnings through 8 p.m. Thursday, cautioning of the risk of heat-related illnesses.
Schoenfeld said a lack of overnight recovery and days of hot weather can “really build and stress the body over time, especially for the elderly and other vulnerable folks like the very young.”
The Los Angeles Department of Public Health is urging residents to hydrate, avoid going outside during the hottest hours of the day, use an umbrella and wear lightweight clothing if you must go out — and take frequent breaks in air conditioned spaces. The county has dozens of cooling centers open.
The heat is expected to relent a bit by the weekend with temperatures in the mid-80s and even a chance of light showers Sunday as Hurricane Rachel continues its path across the Pacific Ocean.
But Swain, the climate scientist, said models suggest that temperatures won’t decline that much as October continues.
“This is not a cool autumn by any means,” he said.