High pressure building over the western states will bring hot and dry weather to Southern California this week, with a Santa Ana wind pattern setting up Sunday, elevating the fire weather threat through much of the week, the National Weather Service said.
Offshore flow will be strongest late Sunday through Monday morning over the mountains and foothills, forecasters said. Winds will weaken Tuesday through the remainder of the week, but the heat and low humidity will continue.
Gradual cooling will occur next weekend as the high pressure starts to break down.
Sunday’s high temperatures along the coast will be around 74 degrees, with overnight lows of 57-65, the NWS said. Inland highs will be 76-81 and the western valley highs will be 79-84 with overnight lows of 54-61. In the foothills, highs will be 87-92.
Mountain highs will be 84-91 with overnight lows of 54-64. Gusty winds of up to 35 mph are expected in the mountains overnight.
Desert highs will be 99-104 with overnight lows of 66-75.
Satellite images Sunday morning showed low clouds continuing over coastal areas and western valleys, the weather service said. High clouds were moving to the southwest across the region and low clouds should scatter out late morning, but may stick around the immediate coast through the afternoon hours.
Sunday will be a transition day as weak offshore flow begins to surface over the mountains and foothills, while onshore flow prevails over the coast and valleys, the NWS said. A slight warming will occur Sunday for inland areas, with coastal areas remaining about the same as Saturday.
The heat will be more noticeable Monday, especially west of the mountains.
The hottest days appear to be Tuesday through Thursday.
A red flag warning was issued Sunday by the NWS, effective from 5 a.m. to 5 p.m. Monday, for San Diego County mountains and valleys. The weather service is predicting lowest daytime humidity of 10 to 15 percent.
“Any fires that develop will likely spread rapidly,” forecasters said. “Outdoor burning is not recommended.”
A red flag warning means that critical fire weather conditions are either occurring now or will shortly, the NWS said. A combination of strong winds, low relative humidity and warm temperatures can contribute to extreme fire behavior.
Although the winds will be weaker Tuesday through Friday, a weak offshore flow, combined with low humidity and dry fuels will elevate the fire weather threat through much of the week.
— Story updated at 4:21 p.m. Sunday, Sept. 27, 2020.
— City News Service