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SAN DIEGO (CNS) – Sweltering conditions will persist in the San Diego County mountains and deserts Monday, but cooler weather is expected the rest of the week, according to the National Weather Service.

An excessive heat warning will remain in effect in those two areas until 9 p.m. Monday.

Cooler temperatures will arrive on Tuesday, and thunderstorms will be possible in the mountains and deserts each afternoon from Tuesday through Thursday, forecasters said.

Highs temperatures on Monday are expected to be in the low-70s to low- 80s in coastal areas, the low- to mid-80s in the western valleys, the high-90s to low-100s near the foothills, the high-90s to low-100s in the mountains and the low- to mid-110s in the deserts.

The weather service said the extreme heat will significantly increase the potential for heat-related illnesses, particularly for those working or participating in outdoor activities.

People should be prepared to drink plenty of fluids, stay in an air- conditioned room, stay out of the sun and check up on relatives and neighbors.

While young children and pets should never be left unattended in vehicles under any circumstances, the weather service said that’s especially true during warm or hot weather — when car interiors can reach lethal temperatures in a matter of minutes.

The county has opened nine “Cool Zone” locations to help the public beat the heat. They are located in Alpine, Borrego Springs, Fallbrook, Lakeside, Potrero, Ramona, Santa Ysabel, Spring Valley and Valley Center.

A full list of the locations can be found here.

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