Southern California Braces for Triple-Digit Heat Wave Expected to Last Into Mid-October

A ridge of high pressure is about to turn early October into an extension of summer across California. The National Weather Service says this will be a major and long-lasting event.

Starting Thursday, October 1, temperatures across Southern California will climb well above normal, according to Bloomberg. Downtown Los Angeles is forecast to hit 90°F Thursday and climb as high as 98°F through the weekend. An extreme heat watch covers areas just inland from Los Angeles and San Diego, including parts of Orange, San Bernardino and Riverside counties, running from Friday through next Wednesday, October 7.

CBS News reports the NWS is calling this a "major and long-lasting heat wave," with highs projected to run 10 to 15 degrees above average for early October. CBS LA Chief Meteorologist Paul Deanno told the station this "is not going to be a one or two-day heat event" and that "it's likely going to stay hot for a while." He added that rain relief typically doesn't show up in the region until November.

How Hot, Where

Pasadena is forecast to hit 93°F Thursday, 97°F Friday, and peak at 101°F Saturday, according to the National Weather Service forecast cited by Pasadena Now. Highs are expected to hold near 98°F Sunday and Monday and around 97°F Tuesday, with overnight lows climbing from the mid-50s Wednesday night to 70–72°F by the weekend, offering little overnight cooling.

Riverside County faces a similarly difficult stretch. Patch reports peak daytime highs of 98 to 105°F from Friday through Sunday in the Riverside area, with the Coachella Valley pushing into the 100–105°F range and overnight lows in the mid-70s potentially tying or breaking daily record-high minimum temperatures. The NWS forecast discussion cited by Patch also notes that Tropical Storm Odalys and Hurricane Polo, both near the Baja California peninsula, are keeping temperatures temporarily suppressed in the Inland Empire through Wednesday before the high-pressure ridge takes over Thursday.

The Bay Area is already in it. KQED reports the region has been running above seasonal norms since Tuesday, September 29, with highs in the mid-80s and 90s inland and 70s in San Francisco and Oakland. NWS meteorologist Dial Hoang told KQED there's "no end in sight" and that San Francisco could see its first 10-day stretch of consecutive 70-degree days since October 2015. Hoang said temperatures could eventually reach triple digits in some inland spots depending on how much the ridge strengthens by mid-October.

One outlet's numbers run hotter than others: reporting attributed to the Gokhshtein research desk put downtown Los Angeles near 100°F through Friday and forecast San Fernando Valley readings as high as 110°F, alongside Bay Area cities hitting 95°F on Tuesday. Those figures run above the Bloomberg and CBS forecasts for the same days. Inland valley readings can diverge sharply from downtown or coastal numbers even within the same metro area.

Fire Risk and Power Demand

Bloomberg notes the heat is pushing up electricity demand at the same time it's raising wildfire risk, as dry offshore winds and low humidity combine with the heat. The Gokhshtein reporting adds that Sacramento, Stockton and Modesto have already surpassed their prior calendar-year records for triple-digit days. Statewide, roughly 1 million acres have burned so far this year, according to that same reporting.

That same coverage noted Governor Gavin Newsom recently vetoed legislation that would have required climate resilience plans for schools, simplified workers' compensation claims for farmworkers suffering heat illness, and exempted 2021 Dixie Fire and 2022 Mill Fire settlement recipients from state taxes on that money. No reasoning from Newsom's office for the veto appears in available reporting.

What's Still Unknown

Forecasters aren't agreed on how long this lasts. CBS LA meteorologists said computer models remain split, with some projecting 7 to 10 days of heat and others keeping Southern California abnormally hot through October 15. Confidence in the models is expected to firm up as the event gets closer, according to that reporting.

For now, the NWS advises residents across the affected counties to stay hydrated, limit outdoor exertion during peak afternoon hours, and check on elderly neighbors, farmworkers and pets, particularly in homes without air conditioning where overnight lows in the 70s will offer little relief.