A Hot Time Guaranteed for the Weekend : Weather: Searing, smoggy air has settled over the county. Temperatures in the low 90s expected.

Throngs of visitors to the air show at the El Toro Marine Corps Air Station this weekend will have to take the heat--literally.

A mass of hot, smoggy air has settled over Orange County and the rest of Southern California, with highs in Santa Ana and El Toro expected to be in the low 90s and in the mid-70s at the beaches, said Steve Burback of WeatherData Inc., a forecasting service used by The Times.

Orange County suffered the year’s first unhealthful bout of smog Friday afternoon--a week before “smog season” officially begins on May 1--with more of the same expected this weekend. “The air mass hasn’t changed much in days,” Burback said. “With more heating and no clouds, the more there will be a smog and haze problem. The sky is going to be that off-white, creamy color.”

El Toro, scene of a military air show today and Sunday, was already the warmest spot in Orange County by Friday, when it posted a high of 88 degrees.

WeatherData’s Burback said lows tonight and Sunday are expected to range from the mid-50s to the low 60s.

On Friday, ozone--the caustic, lung-irritating main ingredient of smog--reached a level of 163 on the Pollutant Standards Index in north Orange County and 150 in central Orange County. That level is considered unhealthful, and people are advised to refrain from outdoor activity.

It was not bad enough, however, to trigger a first-stage smog alert, which requires a reading of 200.

Air quality officials predict that Orange County will suffer unhealthful smog levels today. Friday’s highs included 85 degrees in Santa Ana, 82 in San Juan Capistrano, 78 in Laguna Beach and 71 in Newport Beach.

Times staff writer Marla Cone contributed to this story.

DANGER ZONE Lifeguards brace for extra rescues with riptides and bigger hot-weather beach crowds. A1