Hot, humid conditions will grip Los Angeles County through at least Thursday, with forecasters warning that unusually high overnight temperatures and elevated moisture will make the heat feel more oppressive than the daytime numbers alone suggest.
The National Weather Service issued a Heat Advisory effective through Thursday, Sept. 10, covering the Malibu Coast, Los Angeles County beaches, the Los Angeles inland coast, the western and eastern Santa Monica Mountains, Calabasas and Agoura Hills, the west and east San Fernando Valley, the San Gabriel Valley, and the Palos Verdes Hills.
According to the NWS Los Angeles/Oxnard office, a weak offshore pressure gradient is limiting the region's usual sea breeze, allowing temperatures to climb even as lingering moisture from former Hurricane Marie pushes humidity levels well above normal. Forecasters said that combination will make the heat "feel quite uncomfortable across the area," with advisory-level conditions likely across the Los Angeles Basin.
Overnight lows are expected to stay unusually warm as well, with widespread readings in the 70s and some areas in the foothills reaching into the 80s.
Los Angeles County Public Health officials urged residents to take precautions, warning that heat is a leading cause of weather-related death nationally. "Heat causes more deaths in the U.S. annually than floods, storms, and lightning combined," said Dr. Muntu Davis, the county's health officer, adding that older adults, young children, outdoor workers, athletes and people with chronic medical conditions face the greatest risk.
Officials said residents should call 911 immediately if someone shows signs of heat stroke or heat exhaustion, including confusion, fainting, hot or red skin, a body temperature of 103 degrees or higher, a rapid pulse, headache, dizziness or nausea.
Public Health recommended that residents stay hydrated throughout the day, avoid outdoor activity during peak heat hours, wear lightweight and light-colored clothing, and use sunscreen when outdoors. Officials also warned that vehicles can become dangerously hot within minutes and urged residents never to leave children or pets inside a parked car, even briefly, saying anyone who sees a child or pet alone in a vehicle should call 911.
Residents without air conditioning were encouraged to use cooling centers, libraries, shopping malls or other air-conditioned spaces, or to call 211 for help locating one. The county said cooling centers, splash pads and community pools are available for those without access to air conditioning, with locations listed at ready.lacounty.gov/heat.
The heat threat is expected to expand Wednesday, when additional Heat Advisories take effect for Ventura County's coasts and valleys, the Santa Clarita Valley, and all of Santa Barbara and San Luis Obispo counties, remaining in place through Wednesday evening. Forecasters said there is a 20% to 30% chance humidity levels could climb high enough Wednesday to trigger heat warnings, a more serious designation than an advisory.
Inland areas of the Central Coast could see temperatures reach 100 to 102 degrees Wednesday as offshore flow develops, with some locations running 20 degrees or more above normal for this time of year, according to the NWS.
Forecasters said relief should begin arriving Friday, as high pressure weakens and onshore flow strengthens, bringing 3 to 6 degrees of cooling to most of the region. Similar cooling is expected Saturday, potentially pushing temperatures a few degrees below normal, with Sunday's temperatures expected to be similar. There is a 20% chance the cooling trend could be delayed by a day, forecasters said. A slight warming trend of 1 to 2 degrees is possible by Monday as onshore flow weakens again.