MYRTLE BEACH — Gas prices have spiked in the Carolinas as some refineries have shut down because of Hurricane Isaac, and those rising prices combined with the storm are creating a one-two punch that likely will prompt some South Carolinians to skip taking a trip this long Labor Day weekend, according to AAA Carolinas.

Gas prices in the Carolinas spiked overnight Tuesday by the largest amount since Hurricane Katrina hit the Gulf Coast seven years ago, according to AAA Carolinas. Prices jumped an average 7.6 cents in the Carolinas to an average $3.58 a gallon Wednesday. The state average was 20 cents a gallon less during Labor Day last year.

In Myrtle Beach, the average was $3.54 Wednesday, up 7 cents from Tuesday, 10 cents from a week ago and 35 cents from a month ago, according to Fuel Gauge Report.

Before the spike this week, South Carolina gas prices have ticked up about a penny a day since July 3, according to AAA Carolinas.

“Pump prices will continue upward in the next few days as Hurricane Isaac directly affects prices in [the Carolinas] due to 90 percent of our gasoline coming from pipelines getting supplied by Gulf of Mexico on-shore refineries getting crude from the Gulf’s oil rigs. Many refineries are shut down and oil rigs have been evacuated,” David Parsons, president and CEO of AAA Carolinas, said in a news release.

Isaac, which came ashore in the Gulf as a Category 1 storm but was downgraded later Wednesday to a tropical storm, hit the Gulf Coast on Wednesday with strong winds and heavy rains. It was moving slowly, soaking some areas with inches of rain.

“The longer Hurricane Isaac lingers in the Gulf, the more prices will increase,” Parsons said. “The spikes will definitely be an inhibiting factor for motorists this Labor Day holiday weekend.”

Officials can’t pinpoint when prices will start declining, saying it depends on how long the hurricane lingers over the Gulf Coast keeping those refineries shut, the damage the storm causes and how long it will take to ramp up production after the refineries come back online, said Angela Daley, spokeswoman for AAA Carolinas.

“After that we may start to see some relief,” she said.

The storm and rising gas prices are putting a cloud over travel this Labor Day holiday weekend in the Carolinas, though the Grand Strand is expecting to have a good summer sendoff.

Lodging occupancy along the Grand Strand this holiday weekend is expected to hit between 70 percent and 80 percent, according to Taylor Damonte with Coastal Carolina University’s Center for Resort Tourism. That’s in line with Labor Day weekend the past two years, when occupancy on those Fridays and Saturdays of the holiday weekend were 82.5 percent last year and 80 percent in 2011, according to the center.

The rainy weather along the Grand Strand is predicted to clear out just in time for the holiday weekend, but remnants from Hurricane Isaac in other areas could keep drivers from making the trip through those less-than-ideal traveling conditions, Damonte said. The beach is expected to have mostly sunny skies Friday, Saturday and Sunday with highs in the mid-80s and no chance of rain, according to the National Weather Service.

“It’s going to be a nice weekend, but we’ve had so much nasty weather for the last week and people have to drive to get here,” Damonte said.

About 424,000 South Carolinians are expected to travel at least 50 miles from home starting Thursday through Monday, about the same number as last year, AAA Carolinas said. The travel group had seen a 5 percent increase in Labor Day bookings before the recent run-up in gas prices and Hurricane Isaac.

“A month ago, we expected a robust increase this year for the Labor Day holiday travel weekend, but with the recent spike in gas prices and the threat of Hurricane Isaac, many last-minute travelers will choose to stay home,” Parsons said.

Myrtle Beach isn’t among the most popular Labor Day destinations for Carolinas travelers, according to AAA Vacations, though its absence from the list initially surprised AAA officials. Most travelers are headed to Asheville, N.C.; Washington, D.C.; Wilmington, N.C.; Atlanta; Boston; Pigeon Forge, Tenn.; Savannah, Ga.; Pittsburgh and Williamsburg, Va., according to AAA Vacations, the group’s travel agency.

Even New Orleans, which is getting hammered by Hurricane Isaac, was among the most popular destinations as determined by bookings in the past month or so, and the hurricane could have changed the plans for travelers headed that way, Daley said.

Myrtle Beach likely isn’t among the most popular destinations because many travelers in the Carolinas have visited the area before and aren’t likely to need the travel agency, Daley said.

The Grand Strand is coming off a strong weekend and week, with occupancy during the weekend hitting 78 percent and reaching 71 percent last week, Damonte said.

“We’ve had a couple of soft weeks but this last week made up for that,” he said.

Broadway at the Beach, which has planned special events for Labor Day weekend, doesn’t expect gas prices to keep visitors away from the complex this weekend, O’Neil McCoy, Broadway’s general manager, said in an email.

“We fully anticipate a busy Labor Day weekend at Broadway,” he said. “It will be the perfect farewell to another successful summer season.”

Contact DAWN BRYANT at 626-0296 or at dbryant@thesunnews.com or follow her at Twitter.com/TSN_dawnbryant.