Worst of brutal SoCal heat wave is here: How long will it last? How bad will it be?

A major new heat wave will peak in Southern California over the next few days, bringing dangerous conditions and fire risk.

Here is what you need to know:

Timing

The heat wave begins Friday and will last through the weekend as a strong ridge of high pressure moves over the area.

“A big ridge of high pressure is associated with warmer temperatures,” said Carol Ciliberti, meteorologist with the National Weather Service in Oxnard. “In this case it’s really high, so it’s giving us very hot conditions.”

Forecasters are calling for highs of 95 to 110 degrees in the valleys, with portions of the Antelope Valley potentially reaching 115 degrees, and 100 to 110 across the Inland Empire and high desert, with the low desert potentially nearing 120 degrees.

The coast will be a bit cooler, but still getting into the 80s.

Overnight temperatures won’t fall much below 70 degrees in many locations near Los Angeles, increasing the risk of heat stress.

Forecasters are calling for a slow cooling trend starting Sunday but warned that temperatures would still be above normal and remain that way for the foreseeable future as the high pressure persists.

Fire danger

The majority of Southern California, except for the immediate coastline, will see an enhanced risk of large wildfires Friday through Sunday, when conditions will be hottest and driest, said Kristen Stewart, meteorologist with the U.S. Forest Service.

Areas of particular concern include the foothills of the San Joaquin Valley and the region’s lower mountain areas, she said.

Beach conditions

Forecasters warned that those seeking to escape the heat with a trip to the beach should take care, as a large south swell from Hurricane Genevieve will continue to result in big waves. Southern California lifeguards reported performing thousands of rescues last weekend amid crowded conditions, rough surf and strong rip currents.

A high surf advisory is in effect through Saturday evening from San Diego County to Ventura County due to a large south swell from Tropical Cyclone Genevieve, with forecasters warning the risks are especially acute for south-facing beaches, including Manhattan Beach to Port Hueneme along the Malibu coast, and from Long Beach to the Palos Verdes Peninsula.

Many areas are seeing strong rip currents, and lifeguards have reported performing many rescues, Ciliberti said.

Health concerns

In addition to causing death and illness directly, extreme heat can exacerbate heart, lung and kidney disease, as well as mental health problems, experts said.

The heat wave was also expected to trigger a multiday smog event in some Los Angeles County regions, with the Air Quality Index potentially reaching unhealthy levels in Glendora and unhealthy levels for sensitive groups, including people with asthma, in the San Fernando, Santa Clarita and San Gabriel valleys, according to the South Coast Air Quality Management District. An ozone advisory was in effect from 10 a.m. Friday through 8 p.m. Sunday.

People can lessen the stress by staying inside somewhere that has air conditioning, taking the shadiest route possible when spending time outside, and submerging themselves in water — even if it’s just a cold foot bath.

People should also stay hydrated and refrain from leaving children or pets in vehicles. Those who must be outside are encouraged to wear lightweight, loose-fitting clothing and limit strenuous activities to the early morning or evening, he said.

Underlying drivers

Although forecasters said this heat wave will be drier than the last one, Southern California has seen a hot and unusually muggy summer, in part due to warm ocean temperatures.

Climate change from the burning of fossil fuels has resulted in hotter, more frequent heat waves, said David Eisenman, professor of medicine and co-director of the UCLA Center for Healthy Climate Solutions.

“Also, importantly, the nighttime doesn’t cool down like it used to, so our bodies are not able to recover in the same way,” he said.