High temperatures in most areas of San Diego County will be 5 to 10 degrees above average on Sunday, but it will be the coolest day for much of the week as a strong high-pressure system engulfs the region.
The National Weather Service forecast calls for the system to bring a prolonged heat wave and elevated fire weather conditions. The fire weather threat, while not critical, will be greatest Tuesday through Friday.
Gradual cooling and increasing humidity will help to ease conditions over the weekend and into next week.
“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 on Sunday were expected to be 69 to 74 along the coast, 81 to 86 in the western valleys, 89 to 94 in the foothills, 88 to 98 in the mountains and 110 to 115 in the deserts.
An excessive heat warning will be in effect from 10 a.m. Monday to 9 p.m. Friday for the deserts.
An excessive heat watch for the mountains and valleys begins Tuesday morning and extends through Friday evening.
Patchy low clouds and fog were expected to continue nights and mornings along the coastal areas through much of the week.
City News Service contributed to this article.