Temperatures will soar to the upper 80s at the coast and the 102-104 range across some inland valleys on Monday and Tuesday as San Diego County experiences its third heat wave in a month, according to the National Weather Service. The above average temperatures are expected to last until the weekend, and monsoonal moisture could return by mid-week. An excessive heat watch will be in effect for all areas but the coast from 10 a.m. on Monday to 7 p.m. on Tuesday. Monday will be the hottest day.