High pressure was expected to weaken Monday in San Diego County, bringing slight cooling from the coast to the mountains and greater cooling spreading inland on the July Fourth holiday, the National Weather Service said.
Areas of night and morning coastal low clouds were predicted to extend inland into the western valleys, the NWS said.
Onshore flow could bring gusty sea breeze winds to the mountains and deserts each afternoon and evening.
The most critical fire conditions were expected Tuesday afternoon and evening with lowest daytime humidity around 5% and strongest westerly wind gusts on the desert slopes of the mountains to around 50 mph during the late afternoon into the evening.
Along the coast Tuesday, it was expected to be partly cloudy with high temperatures from 70 to 74 degrees and 75 to 78 inland, the NWS said. The western valleys were expected to be mostly sunny with highs from 80 to 85 and near the foothills from 88 to 93. It should be mostly sunny in the mountains with highs from 84 to 94. The deserts were expected to be mostly sunny with highs from 108 to 113.
Minor day-to-day changes or slight cooling may continue into Friday and Saturday.
For early next week, high pressure to the east could strengthen and begin to expand westward into Southern California, bringing a warming trend with high temperatures for the deserts next Monday around 5 degrees above average.
The marine layer and onshore flow may continue to moderate the heat toward the coast with areas of night and morning coastal low clouds extending inland into the western valleys at times.
Patchy fog may develop over the coastal waters each night and morning through Thursday. There is about a 20 to 25 percent chance of visibility less than 1 nautical mile, especially Tuesday and Wednesday mornings.
City News Service contributed to this article.