The National Weather Service has issued an excessive heat advisory for the San Jacinto Mountains at least through Saturday night, Sept. 2.

However, while winter is colder and more dangerous in Idyllwild than in the valleys and coastal areas, this heat weather is considered “dangerous” for those areas.

NWS has issued a heat advisory for the San Jacinto Mountains at least through this Friday night. The high pressure that is trapping the heat in Southern California is expected to rebuild Thursday, so the excessive heat warning will continue through Labor Day weekend, according to Alex Tardy of the San Diego NWS.

The NWS Advisory says, “The heat may relent slightly for Thursday into next weekend … but with high temperatures remaining well above average.”

A slight chance of thunderstorms is forecast for any day this week. A high ridge of high pressure brought this sweltering heat to Southern California, according to NWS meteorologist Stephen Harrison.

One advantage of the high-pressure system over Utah is that it blocks Hurricane Harvey from traveling west, Tardy noted.

“The long duration of the heat wave and the lack of significant relief overnight will result in potentially deadly heat for much of the region,” Harrison said Friday in a You Tube video.

A heat advisory, according to the NWS, is a “period of hot temperatures, which is expected [to] create a situation in which heat illnesses are possible.”

NWS advises people to drink plenty of fluids, stay in an air-conditioned room and stay out of the Sun. Also, “check up on relatives and neighbors.”