If you need a reminder that summer begins today, just look at the thermometer.

The first day of summer marks the start of a heat wave that will linger through Sunday across the North Bay, bringing triple-digit temperatures to the area for the first time since September.

Sonoma County’s forecast calls for highs at or near the 100-degree mark through the weekend, with Saturday being the hottest day, the National Weather Service said.

On Saturday, Santa Rosans can expect a high of 103 degrees, while in Cloverdale, the high could reach 105 degrees. Meanwhile, coastal temperatures are expected to top out about 70 degrees, said Steve Anderson, a forecaster with the weather service.

“It will be a good time to go to Lake Sonoma or the Russian River,” he said.

While it’s certainly going to be hot, the North Bay likely won’t see any record-breaking temperatures, Anderson said.

On this weekend’s hottest day — Saturday — the record high for Santa Rosa was set at 107 degrees in 1909, and it looks like it will stay that way, he said.

The heat will dry out any green vegetation remaining from the North Bay’s below-average rainfall, raising the specter of fire, he said.

“It will be hot and dry, but no high winds, so that’s one good thing,” Anderson said. “But, yeah, the hot weather is not going to help things at all.”

Despite excessive heat kicking off the start of the summer season, it isn’t a harbinger of what’s to come. All indications are that this summer’s heat will be near normal, Anderson said.

At Santa Rosa’s Prince Gateway Park Wednesday, 7-year-old Willow Kagey splashed about in the so-called “sprayground” as her mom, Misty Kagey, 35, watched from a shady patch of grass nearby.

The Santa Rosa mother-daughter pair headed to the park to cool off from the 78-degree day.

“I love the summer,” Misty Kagey said. “Just the sunshine and all the fun stuff there is to do. We try to hit all the different parks. We go to the pool.”

The pair plan to head to the water park at Spring Lake Regional Park this weekend, she said.

Parks workers across the county are preparing for what could be their busiest weekend yet, with visitors traveling from all over the Bay Area to beat the heat.

Park rangers will be closely monitoring activity along the Russian River, where by Wednesday staffers had already received a number of phone calls from eager Sonoma County weekenders asking about water conditions, said Scott Bolin, supervising ranger of Russian River beaches.

“The big thing is that people be safe out there and do what they can to be respectful of others,” Bolin said. “Wear life jackets if they can. Be cognizant of where they’re at. With heat factors, too, rangers will be on the lookout for anybody who may be having heat exhaustion. That’s a big one.”