Los Angeles Heat Advisory conditions are set to intensify Wednesday, Sept. 9, as high temperatures combine with elevated humidity across much of Los Angeles County. The National Weather Service expects downtown Los Angeles to reach about 98°F, with heat index values as high as 116°F. Readers will find the timing, affected areas, humidity factor, and official safety guidance below.
Key Takeaways
- The National Weather Service has a Heat Advisory in effect for much of Los Angeles County from 10 a.m. Tuesday, Sept. 8, through 8 p.m. Thursday, Sept. 10.
- Downtown Los Angeles is forecast to reach about 98°F Wednesday, with heat index values as high as 116°F.
- The advisory includes downtown Los Angeles, the San Fernando and San Gabriel valleys, Los Angeles County beaches, Malibu Coast, Palos Verdes Hills, and parts of the Santa Monica Mountains.
- The National Weather Service says humid conditions will add to heat discomfort, with the heat expected to peak Wednesday for most areas.
- Los Angeles County maintains public cooling centers and directs residents to additional air-conditioned facilities during excessive heat.
Los Angeles Heat Advisory conditions are expected to peak Wednesday, when the National Weather Service forecasts the highest temperatures of the current episode for much of the region.
The advisory began at 10 a.m. Tuesday and remains scheduled through 8 p.m. Thursday for a broad set of Los Angeles County zones. The National Weather Service expects temperatures of roughly 85°F to 105°F across the advisory area, about 10 to 15 degrees above normal depending on location.
Humidity is a central part of the forecast. The agency said, “Humid conditions will add to heat discomfort,” and identified Wednesday as the likely peak for most areas.
Wednesday Heat Index Could Reach 116°F
For central Los Angeles, the National Weather Service point forecast shows a high near 98°F on Wednesday. More notably, the same forecast lists heat index values as high as 116°F.
The heat index combines air temperature and relative humidity to estimate how hot conditions feel to the human body. Higher atmospheric moisture can slow the evaporation of perspiration, reducing the body’s ability to cool efficiently and making humid conditions feel hotter.
That distinction matters during the current heat episode because the thermometer alone does not necessarily represent how conditions feel. National Weather Service guidance also notes that heat index calculations generally assume shaded conditions, meaning full sun can add further heat exposure.
Tuesday remains hot as well. The downtown forecast calls for a high near 95°F after a chance of morning showers and thunderstorms, followed by clearing conditions. Overnight temperatures are forecast to fall only to around 73°F before Wednesday’s hotter afternoon.
Thursday is forecast to remain warm but somewhat cooler, with a high near 92°F in central Los Angeles. Friday’s current forecast falls to around 87°F, although National Weather Service forecasts and advisory periods can be updated as conditions develop.
Humidity Broadens the Los Angeles Heat Stress
The Los Angeles Heat Advisory covers a wide section of the county. Affected zones include the Los Angeles County inland coast, including downtown Los Angeles, as well as the San Fernando Valley, San Gabriel Valley, county beaches, Malibu Coast, Palos Verdes Hills, Calabasas and Agoura Hills, and portions of the Santa Monica Mountains.
The forecast range of approximately 85°F to 105°F across those zones also shows that conditions will differ substantially by location. The alert is therefore not limited to the communities that record the county’s highest afternoon temperatures.
Humidity adds another layer to that variation. At 8:40 a.m. Tuesday, the National Weather Service observation for downtown Los Angeles showed 83°F, relative humidity of 54%, and a dew point of 65°F. The heat index at that time was 85°F, before the forecast afternoon high.
As temperatures rise, humidity becomes increasingly important to the apparent temperature. The National Weather Service defines the heat index as the measure of how hot it feels when relative humidity is considered alongside air temperature.
For residents who expect to spend significant time outdoors, hot weather safety tips remain particularly relevant during the hottest hours. Official guidance recommends reducing strenuous activity during periods of excessive heat, maintaining hydration, seeking cooled spaces, and checking on people who may face greater heat-related health risks.
Warm Nights and Workplace Exposure Extend the Risk
The forecast also keeps overnight temperatures elevated. Downtown Los Angeles is expected to remain near 73°F Tuesday night and again Wednesday night before falling closer to 70°F Thursday night.
Los Angeles County identifies older adults, infants and young children, and people who overexert during work or exercise among groups at higher risk during excessive heat. Ready LA County maintains a cooling-center directory and says listed locations generally provide air conditioning, bathrooms, drinking water, and public access during their posted hours.
Residents can also use other public air-conditioned facilities when necessary. Los Angeles County says residents can call 211 for cooling-center information and other emergency-preparedness resources, while City of Los Angeles heat resources are available through 311.
Workplace exposure is another part of the heat picture. Los Angeles worker heat risks become especially relevant for jobs that require prolonged periods outdoors or in hot indoor environments.
California heat illness regulations require protections at covered indoor and outdoor workplaces. Cal/OSHA says outdoor shade must be available when temperatures exceed 80°F, while specified industries must use additional high-heat procedures when temperatures reach or exceed 95°F. The state’s indoor heat standard applies to most indoor workplaces when temperatures reach 82°F.
Those requirements can affect workers in construction, landscaping, warehouses, restaurants, manufacturing facilities, and other settings where employees may have limited control over their heat exposure. Cal/OSHA requires measures that can include access to drinking water, shade or cool-down areas, preventive rest periods, and worker training depending on the workplace and temperature.
The current Los Angeles Heat Advisory therefore carries different levels of exposure across the county. Residents near the coast, people traveling through downtown, employees working indoors without adequate cooling, and outdoor workers may encounter different temperatures, but extended heat and humidity can increase physical strain.
By late Thursday, the current National Weather Service forecast shows temperatures beginning to ease in central Los Angeles. Until then, Wednesday remains the central period of concern, with a forecast high near 98°F and heat index values potentially reaching 116°F in downtown Los Angeles.
Frequently Asked Questions
How long is the Los Angeles heat advisory in effect?
The Los Angeles Heat Advisory is scheduled from 10 a.m. Tuesday, Sept. 8, through 8 p.m. Thursday, Sept. 10, for the affected Los Angeles County zones. The National Weather Service has identified Wednesday as the expected peak for most areas.
How hot could downtown Los Angeles get Wednesday?
The National Weather Service point forecast for central Los Angeles calls for a high near 98°F on Wednesday. Heat index values could reach as high as 116°F at that location.
Why is humidity important during this heat event?
Humidity affects how efficiently perspiration evaporates from the body. The National Weather Service uses temperature and relative humidity together to calculate the heat index, which estimates how hot conditions feel.
Which areas are included in the advisory?
The advisory covers downtown Los Angeles and the county inland coast, along with the San Fernando and San Gabriel valleys, Los Angeles County beaches, Malibu Coast, Palos Verdes Hills, Calabasas and Agoura Hills, and portions of the Santa Monica Mountains. Conditions and temperatures will vary across the affected zones.
Where can Los Angeles residents find cooling centers?
Ready LA County maintains a directory of public cooling centers and says residents can call 211 for local cooling-center information. City of Los Angeles residents can also use 311 to identify city heat-relief resources.
