Weekend Could Be Stormy as Well as Sticky

Relative humidity and thunderstorm activity diminished here Thursday when tropical depression Guillermo traveled north but, according to National Weather Service forecasters, a new influx of moisture may generate stormy weekend weather.

A high-pressure system that has been influencing San Diego County weather, centered Thursday in the Four Corners area of Arizona, Utah, Colorado and New Mexico, was beginning to move west. According to forecaster Ray Robben, the shift will move the county out of a “bottom side” position in the high-pressure system.

“The moisture line will be advancing toward us. At this time of the year, moisture and thunderstorms build up in the mountains of Mexico and eastern Arizona--but they usually stay there,” Robben said. Since last year, that humid air has been heading toward San Diego more frequently, he said.

He said conditions would be favorable for isolated thunderstorms in the mountains and deserts beginning late today. Thunderstorms could be pushed into the valleys by Sunday. “It all depends on the location of the high,” Robben said.

Humidity that dropped to about 50% at Lindbergh Field on Thursday is expected to reach about 80% this morning when fog clings to the shore. Some moisture will evaporate by afternoon, but above-average humidity levels are expected through the weekend.

An onshore sea breeze should protect beach areas and the immediate coastal strip from uncomfortably hot temperatures, but inland valley temperatures will continue to sizzle--reaching as high as 102 degrees.

Day and night temperatures that have been above average for nearly two weeks are expected to continue through the weekend. The July 11 norm at Lindbergh Field is a high of 75 and a low of 65. On Thursday the high was 84 and the nighttime low was 72.

Temperatures through Sunday at the beach should be balmy, with highs in the 70s and an ocean water temperature of about 68 degrees. Light, variable morning winds will blow up to 20 knots from the west to southwest in the afternoon and evening today.

Coastal strip highs are expected to be 79 to 85 degrees, with lows between 67 and 73 degrees.

Night and morning clouds and hot, sunny afternoons are expected inland, with temperatures at night dropping to the 60s.

Mountain highs in the 80s will fall to 55 to 65 degrees at night. Desert temperatures that will reach 104 to 114 degrees will show little cooling at night, with lows in the 80s.