Temperatures topped 100 in San Diego County on Thursday and are expected to keep climbing this weekend, when inland areas may swelter with sunny skies and highs more than 10 to 20 degrees above the June norm.
Forecasters said area growers, who earlier this week complained that the cool weather slowed crop growth, were cheered Thursday when temperatures leaped to 100 degrees in Fallbrook, 97 in Escondido and 93 in Vista.
In other parts of the county, the temperature reached 99 in El Cajon, 96 in Lemon Grove, 101 at the Wild Animal Park, 94 at San Diego State University and 110 in Borrego Springs.
Closer to the coast, temperatures were slightly cooler--80 degrees at Lindbergh Field, 79 in Chula Vista, 88 in National City, 80 in Coronado, 70 degrees in Del Mar and only 65 in Oceanside.
A high-pressure system building off the California coast this week has pushed out the cool weather and winds that chilled San Diego last weekend, as temperatures did not rise above 68 degrees Saturday and Sunday.
Summer isn't due for two weeks, but the weather this weekend may remind San Diegans of last summer's siege of muggy heat. According to forecaster Wilbur Shigehara, humidity in the 45% to 55% range along the coast and 25% to 45% inland will make the heat more uncomfortable.
Along the coast, however, the heat may be tempered by cooler ocean air trying to push its way inland.
"We do have a fight going on between the marine air and the high temperatures. If the sea breezes win out, beach temperatures might not reach 80," Shigehara said. "The only place to stay cool this weekend will be along the coast."
Gentle westerly winds of 8 to 15 m.p.h. will blow in off the ocean through Sunday, but forecasters said that areas more than five miles inland may not have the benefit of a breeze to disturb the hot air.
Ocean air will generate night and morning clouds that may become hazardously thick at night and early morning, forecasters said. The warmer temperatures have the effect of pushing low clouds to the ground, creating dense fog.
Low clouds backed up against the mountains, however, should evaporate rapidly in the early morning as the air warms, Shigehara said.
High temperatures along the coast are expected to be in the 80s through Sunday with lows between 58 and 64 degrees.
Shigehara said inland highs are expected to be between 90 and 110 degrees with lows from 58 to 64 degrees.
Temperatures in the mountains may reach 88 during the day but will cool to around 50 degrees at night. Desert highs between 106 and 112 degrees are expected to drop to the 70s at night.
Temperatures at Lindbergh Field have not been this hot for more than two months. Highs of 87 and 88 degrees were recorded April 1 and 2.