Holiday Hordes Expected to Jam Beach, Freeways : Weekend: As summer sets, lifeguards, CHP brace for a busy four days with sun-seekers and travelers. Motorists are advised to leave early--and sober.

Orange County residents by the thousands are expected to hit the beaches this Labor Day weekend, taking advantage of summer’s traditional last hurrah and avoiding inland heat and smog.

In San Clemente, Marine Safety Lt. Bill Humphreys predicted especially big crowds on the beach this weekend.

“I think we’ll have larger crowds because the weather has been much nicer this week,” Humphreys said. “It’s been very warm in the inland areas, and I think a lot of those people who live there will be coming to the beach.”

Humphreys said the sun broke out about 9:30 a.m. Thursday on San Clemente beaches, giving beach-goers a full day of sunshine. “On most of the days this summer it’s been after noon--or never,” Humphreys noted.

But the sun, which has been playing peekaboo all summer long, will again hide behind morning clouds before a midmorning or afternoon appearance, said weather forecasters.

“It’s a ridge of high pressure affecting us (Thursday), but it’s going to break down over the weekend and we’re expecting more low clouds and fog, especially along the coast,” said Marty McKewon, a meteorologist for WeatherData Inc., which forecasts the weather for The Times.

Beach temperatures warmed to 76 degrees on Thursday, prompting lifeguard officials to order full crews this weekend along the county’s 42-mile coastline. Temperatures will be in the upper 60s to mid- to upper-70s along the coast. Inland temperatures should range from the upper 70s to the upper 80s.

Smog will again plague Orange County, especially in La Habra and Anaheim and other North County cities, said Joseph Cassmassi, a senior meteorologist for the South Coast Air Quality Management District in El Monte.

The AQMD is predicting first-stage smog alerts for the San Gabriel, Riverside and San Bernardino areas today. However, with cooler temperatures expected through the weekend, Cassmassi predicted some improvement by Saturday and Sunday.

On Monday, all city, county, state and federal offices will be closed. Post offices, schools and banks also will take the day off.

Drivers leaving town today for the deserts and the Colorado River are advised by the California Highway Patrol to leave early.

“We expect the Santa Ana and the Riverside freeways to be very busy all day,” said Angel Johnson, a CHP spokeswoman in Santa Ana.

Throughout the weekend, CHP officers will be focusing on drunk drivers, Johnson said. Last year, officers arrested 366 motorists on suspicion of drunk driving over the Labor Day weekend in Orange County. Johnson predicted that the number will be larger this year.

“We’re going to get more because we’ve got more patrols and more people out driving,” she said. “I really can’t see anything wrong with just staying home this weekend. If you’re going to drink, drink at home.”

Johnson said that of the state’s 68 freeway deaths during last year’s holiday, three occurred in Orange County. Half of the 68 people killed were not wearing seat belts, she said.

John Wayne Airport officials said they expect a surge in travelers over the Labor Day weekend but nothing like the crowds at Thanksgiving and New Year’s.

With the new Thomas F. Riley Terminal open, holiday problems that plagued the cramped, older passenger facility simply aren’t expected, said airport spokeswoman Courtney Wiercioch.

A year ago, the old terminal handled 15,714 passengers on the Friday that started the Labor Day weekend. Passenger volume is about 25% over last year, but the building is 10 times bigger.

“We’re expecting more passengers this year, just because we have more of everything with the new terminal,” Wiercioch said. “But we think the facilities will handle the extra people very well.”

Times staff writers Bill Billiter and Jeffrey A. Perlman contributed to this story.