High pressure could push temperatures in parts of San Diego County into the low hundreds Tuesday while showers and thunderstorms caused by tropical moisture will increase the risk of flash flooding throughout the region.
A National Weather Service heat advisory is set to take effect at noon Tuesday and extend until 6 p.m. Wednesday in coastal areas and the valleys. A flash flood watch for the mountains and deserts will extend from noon Tuesday through Thursday evening.
Highs of 82 to 87 degrees are forecast Tuesday for the coast, 90 to 95 degrees in inland areas, 94 to 99 in the valleys, 88 to 96 in the mountains and 103 to 108 degrees in the deserts. Slightly higher temperatures are expected Wednesday along the coast and in the valleys.
"High pressure aloft will bring hot daytime weather through Thursday with Wednesday expected to be the hottest day," according to the weather service. "Nights will be warm as well with low temperatures 5 to 10 degrees above average."
A chance of afternoon and nighttime showers and thunderstorms was also in the forecast for the mountains and deserts. Forecasters said a 50 percent chance of measurable precipitation in the mountains should drop to around 20 percent overnight, and a 20 percent chance of measurable precipitation in the deserts should remain unchanged through Thursday.
"Tropical moisture will continue to increase across far southern California into Thursday, bringing and increasing chance of afternoon and early evening thunderstorms to the mountains, deserts and portions of the Inland Empire with locally heavy rainfall and flash flooding possible," forecasters said.
Forecasters said areas in and below recently burned areas would be particularly susceptible to heavy runoff and debris flows should strong thunderstorms develop nearby.
They also urged people to protect themselves and their loved ones against dehydration, heat stroke and other heat-related illnesses. Residents were advised to stay well-hydrated, avoid working in the sun, check on neighbors and relatives — especially the elderly — and provide plenty of water to pets and livestock.
