RIVERSIDE (CNS) - Scorching heat is expected again Thursday, Aug. 20 throughout Riverside County, but relief will arrive this weekend, according to the National Weather Service. High pressure over the southwestern United States will slowly weaken as it moves southward into Arizona, forecasters said. An excessive heat warning will remain in effect until 10 p.m. today in the Riverside metropolitan area, the Riverside County mountains, the San Gorgonio Pass near Banning and the Coachella Valley. The NWS urged residents to drink plenty of fluids, stay out of the sun and check on relatives and neighbors. Also, young children, seniors and pets should be never be left unattended in a vehicle, with car interiors able to ``reach lethal temperatures in a matter of minutes,'' according to the NWS.