Breaking a string of cooler-than-average temperatures, San Diego County weather warmed Thursday--beginning what forecasters predict will be a spell of hot, muggy weather.
Thursday's high of 78 degrees at Lindbergh Field--the first above 75 since Aug. 6--reflected the breakdown of an upper-level trough that has fostered cooler weather. The weakening system, an odd pattern for this time of year, also generated last weekend's spring-like overcast skies and misty air.
"Weather will take a wide swing this weekend. A high pressure will bring a good warming trend--and some areas will be hot," National Weather Service forecaster Wilbur Shigehara said.
A building high-pressure system, bulging into Southern California from Texas, is expected to dominate weather here through the weekend. Not only will temperatures rise from below average to 8 to 10 degrees above the norm, but the pattern is expected to invite subtropical moisture from the south.
Sound like last summer? According to Shigehara, uncomfortable, muggy weather may invade the county by day, but sleepers will be spared the record-high nights associated with last summer's blast.
The familiar late-night and early morning low clouds should be confined to within four miles of the coast through the weekend, where thick fog should clear by 9 a.m. Clear, cool nights are expected inland.
Sunny, warmer days are predicted for the county, but Shigehara said forecasters are looking to the south for cloudiness that may arrive with the subtropical air mass. High clouds could scatter across the county, and the unstable air might generate thunderstorms in the mountains and deserts.
At the beach a light breeze of 8 to 15 m.p.h. and a mild surf of 1 to 3 feet are expected. The water temperature hovers at a cool 67 degrees, Shigehara said. Daytime highs up to 76 today may reach 80 over the weekend.
Highs along the coast, up to 83 today, are expected in the mid-80s by Saturday, with nighttime lows in the 60s.
Inland valley highs expected in the 88- to 98-degree range today may reach 100 over the weekend. Nighttime lows will be 59 to 67 degrees.
Mountain highs are expected to be in the 80s with lows in the 52- to 62-degree range. Desert highs between 108 to 113 degrees today may inch up to 115 over the weekend. Lows are expected to be 78 to 86.
Forecasters said relative humidity will not jump, but the rising temperatures together with the moisture will make the air feel warmer--raising the high on the National Weather Service's "comfort index," a measure used frequently during last summer's persistent heat wave.