Much of San Diego County under heat advisory later this week, extreme heat in deserts

SAN DIEGO (FOX 5/KUSI) — Much of San Diego County will be under a heat advisory later this week, while extreme heat is forecast for the desert areas, marking the first major heat wave of the summer.

Monday started a gradual warmup across San Diego County, while temperatures are forecast to increase slightly Tuesday, peaking Wednesday and Thursday.

Temperatures in inland cities will reach around 100 degrees by Wednesday and Thursday, while desert areas will near 115-120 degrees. Coastal San Diego areas will also see a warmup later in the week, but are only forecast to reach the upper 70s and low 80s.

By the weekend, inland areas will be around 10 degrees cooler with a high around 85 degrees forecast for Saturday and Sunday.

Heat Advisory

The National Weather Service (NWS) has issued a heat advisory for much of inland San Diego County from 10 a.m. Wednesday to 8 p.m. Thursday. Temperatures are expected to reach 97 to 101 degrees in valley areas and the cities of La Mesa, Escondido, El Cajon, San Marcos, Santee and Poway.

NWS San Diego says the hottest temperatures are expected east of Interstate 15, and noted the high temperatures can cause heat illness.

Extreme Heat Warning

At the same time, from 10 a.m. Wednesday to 8 p.m. Thursday, San Diego County deserts will be under an extreme heat warning, NWS reports.

NWS advises because of the high temperatures expected, up to nearly 120 in some areas, that the risk of heat-related illness will be high, especially for people who are sensitive to heat, or without proper cooling and/or adequate hydration.

There will also be increased relative humidity during this warmup, adding some moisture in the air which can make conditions feel warmer, NWS says.

When in an area under a heat advisory or warning, NWS advises to drink enough fluids, stay in air conditioning, stay out of the sun, and to check on relatives and neighbors as hot temperatures can cause heat illnesses.