Daniel Trouwborst, a Palace Playland employee in Old Orchard Beach, prepares a balloon-pop game Friday for a Memorial Day weekend opening. Visitors to Maine reached 36.7 million last year, up 2.5 percent from 2016. (Ben McCanna/ Portland Press Herald)

Visitors started flooding into Maine on Thursday to enjoy the long Memorial Day weekend, the unofficial start to the state’s tourism season.

The next few months are critical for Maine’s tourism industry and state officials are optimistic more people will visit the state in 2018, continuing a five-year growth trend.

“Two-thirds of our business does come during the summertime, but we have seen remarkable growth in the offseason, particularly winter and fall,” said Steve Lyons, director of the Maine Office of Tourism. The state does not make predictions, but its industry partners report strong bookings for the upcoming season, Lyons said.

The number of visitors coming to Maine reached 36.7 million last year, a 2.5 percent bump from 2016. That growth was less than half of the 6 percent average annual growth rate in the previous four years.

Last year’s increase is closer to national tourism trends and officials expect strong future growth, Lyons said.

“As much as we would like to keep 6 percent growth, I think it is a very difficult number to maintain,” Lyons said. “There is some mystique about Maine that really makes people want to visit. I think that will continue.”

Almost 42 million Americans, including 1.9 million New Englanders, will be on the roads this Memorial Day weekend, according to AAA. It is the highest number of travelers in more than a dozen years and a 5 percent bump from 2017.

Travel is surging even as gas prices hit a four-year high. The average price for a gallon of regular gas in Maine was $2.95 on Friday, according to price-tracking website gasbuddy.com. That’s about 50 cents per gallon higher than last year.

Memorial Day weekend traffic builds Friday on Interstate 95 in Kennebunk. (Jill Brady/Portland Press Herald)

The Maine Turnpike Authority expects at least 978,000 vehicles on the highway over the long weekend, almost 2 percent more than the same time last year. Heavy southbound traffic is expected as visitors leave the state Monday afternoon, raising the possibility of traffic jams at the Piscataqua River Bridge to New Hampshire.

Maine’s tourism businesses are hoping for another blockbuster year in 2018. However, concerns linger that an inadequate seasonal workforce could hurt an industry that supports about one in every six jobs in the state and brought in $6 billion of direct tourism spending last year, according to the Maine Office of Tourism.

Hotels, bed-and-breakfasts and vacation rentals are looking forward to another strong season, said Steve Hewins, president and CEO of the Maine Innkeepers Association.

Taxable lodging sales in Maine crested $1 billion for the first time last year and the association projects higher sales in 2018.

“This time of year breeds optimism,” Hewins said. “Bookings in the spring and winter were pretty strong. I think that gives people a lot of confidence that it will continue through the rest of the year.

“We basically want to be able to expect that nothing has plateaued yet in this industry and the demand for people coming to Maine remains strong,” he said.

Old Orchard Beach residents Jason Greenbaum and Annie Stevens eat lunch at Mike’s All American Meal on The Pier at Old Orchard Beach on Friday. The head of the the Maine Innkeepers Association says, “This time of year breeds optimism.” (Ben McCanna/ Portland Press Herald)

Summer spending is critical for Maine’s hospitality industry. Consumers spent $1.5 billion on lodging and restaurants in June, July and August last year, 40 percent of annual taxable sales, according to data from Maine Revenue Services. While summer is Maine’s dominant tourism season, more visitors are coming at other times, especially in the fall. Businesses that once reliably closed after Labor Day weekend in early September now stay busy through Columbus Day, more than a month later.

A reliable seasonal workforce is the one “wild card” that could disrupt another season of record-breaking earnings, Hewins said. Another year of federal hold-ups for temporary foreign worker visas and a tight labor market have left some seasonal businesses scrambling to find enough workers to keep hotel rooms open and restaurant customers served.

“Having enough staff to be open all the hours they want to be open is going to be a big issue, for sure,” Hewins said.