Newport Beach residents face an extreme heat warning starting Saturday, Oct. 3, with coastal temperatures expected to reach the mid-80s to around 90 degrees.

The National Weather Service upgraded an earlier watch to a full warning on Thursday, Oct. 1. The warning takes effect at 10 a.m. Saturday and runs through 8 p.m. Thursday, Oct. 8, according to the Orange County Register. Separate warnings cover inland Orange County, where highs could reach the mid-90s to near 100, and the Santa Ana Mountains, where the NWS forecast highs in the mid-90s to 104.

Along the coast, the NWS San Diego office said overnight lows will stay in the lower to mid-70s, offering little relief after dark.

Sunday, Oct. 4 is the expected peak. Triple-digit temperatures are forecast in parts of Los Angeles and Ventura counties, according to the Los Angeles Times.

"This is one of the longer-duration ones that I've seen in my time at this office," NWS Oxnard meteorologist Rose Schoenfeld told the Times. Schoenfeld said the heat wave, driven by high pressure and a lack of wind, does not have a clear cutoff. Weather service models suggest it could last through mid-October.

The NWS described the risk as "Major to Extreme" for inland coastal areas and western valleys, with at least moderate heat risk along the coast.

The agency urged residents to drink plenty of fluids, stay in air-conditioned spaces, avoid direct sun and check on relatives and neighbors. The NWS also warned against leaving children or pets in unattended vehicles, noting car interiors can reach lethal temperatures within minutes.

Newport Beach has two designated cooling centers listed on the Orange County cooling center directory: the Civic Center Community Room at 100 Civic Center Drive and the Oasis Senior Center at 801 Narcissus Ave. Both are open Monday through Friday, 8 a.m. to 5 p.m. Whether the city will extend hours or open weekend locations for this event has not been announced.

The heat warning arrives after what Newport Beach lifeguard Chief Brian O'Rourke described as an unusually demanding summer. O'Rourke told the Orange County Register on Sept. 2 that lifeguards had already made more than 4,000 ocean rescues, well above the typical 3,000 for a full season. His comments addressed surf hazards ahead of Labor Day weekend, but the pace underscores the compounding pressure on the city's public safety teams heading into the heat event.

Residents can reach the Civic Center Community Room at 949-644-3140 and the Oasis Senior Center at 949-644-3244.