Sunday's high temperatures in San Diego County were forecast to be five to ten degrees above average, but it will be the coolest day for much of the week as a strong high-pressure system comes into the region, the National Weather Service said.
The forecast calls for the system to bring in a prolonged heat wave and elevated fire weather conditions. The fire weather threat, while not critical, will be greatest Tuesday through at least Friday, the NWS said. Gradual cooling and increasing humidity will help to ease conditions over the weekend and into next week.
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"The main concerns are with the inland push of the sea breeze in the afternoons and evenings, especially through and below the desert passes and the coming extreme heat, creating the potential for large, plume-dominated fires over the far inland valleys and mountains," the weather service said.
High temperatures in coastal areas Sunday were expected to be 69-74 degrees with overnight lows of 56-62, the NWS said. Western valley highs will be 81-86 and 89-94 in the foothills with overnight lows of 53-60.
Mountain highs were expected to be 88-98 with overnight lows of 55-65. Highs in the deserts will be 110-115 with overnight lows of 75-83.
An excessive heat warning was issued from 10 a.m. Monday to 9 p.m. Friday for San Diego County deserts.
An excessive heat watch was issued from Tuesday morning through Friday evening for San Diego County mountains and valleys.
Patchy low clouds and fog were expected to continue nights and mornings along the coastal areas through much of the week.
The high-pressure ridge over the Southwest was predicted to keep it hot well inland into next weekend, with cooling expected across the entire region early next week, the NWS said.
