The record-breaking heat roasting parts of San Diego County is expected to peak Wednesday as humidity generated from slow moving storms adds to the already uncomfortable conditions and threatens possible flash flooding.
A high of 92 degrees in Chula Vista Tuesday amid a National Weather Service heat advisory topped a previous record of 89 degrees set on Sept. 8 last year.
The heat advisory for the coast and the valleys will remain in effect until 6 p.m. Thursday. A flash flood watch for the mountains and deserts will also extend through Thursday evening.
Forecasters said high pressure aloft would keep conditions toasty Wednesday with high temperatures in some areas up to 15 degrees above average. The low deserts are expected to remain closer to normal, but muggy.
Highs of 85 to 90 degrees are forecast Wednesday for the coast, 95 to 100 degrees in inland areas, 97 to 102 in the valleys, 87 to 95 in the mountains and 101 to 106 degrees in the deserts.
A chance of afternoon and evening thunderstorms is also in the forecast for areas other than the coast. The weather service pegged the chance at measurable precipitation at 20 percent in the valleys, 40 percent in the deserts and 50 percent in the mountains.
Forecasters said the sea breeze and east winds would converge Wednesday afternoon, which will allow storms to develop. Locally heavy rainfall and flash flooding could be possible near the storms.
"Light steering winds today will result in slow moving storms and a threat of flash flooding, especially over the mountains, deserts and portions of the Inland Empire," according to the weather service.
Areas in and below recently burned areas would be particularly susceptible to heavy runoff and debris flows should strong thunderstorms develop nearby.
Forecasters 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.
Authorities also warned against leaving children or pets in parked cars, which can quickly become death traps in high heat.
Cooler weather is expected to spread inland from the coast starting Friday.
