The optimum word is "possibly."

It captures the capricious spirit of the possibly annual Hawaiian Christmas Looong Distance Invitational Rough-H20 Swim, an adventure intended to be taken seriously for serious fun.

Sunday’s 4.33-mile (7-kilometer) race is scheduled to be held for the 32nd time in 33 years. The probability is close to 100 percent that the 42 entered swimmers will get the go-ahead to go from San Souci Beach to the outer Ala Wai Harbor channel buoy and return.

For sure? The unpredictability of that matches the unpredictability of the conditions. It’s Mother’s Nature’s playtime, where the water can change in a matter of strokes.

That is part of the allure.

"You just never know what’s going to happen that day," said Hawaii’s Linda Kaiser, acknowledged as one of the pioneers of ocean swimming and one of two people to swim all nine of Hawaii’s major channels. "One time, it took four hours to go down and a half-hour to come back.

"Sometimes you’re halfway back to the finish and you’re asking yourself, ‘Why am I doing this?’ Then after a couple of months, you start planning to do it again."

There is a mystique equated with a journey to Oz to see the wizard, according to Rick Heltzel, who has won the event a record 12 times. The entry process is a bit different with applicants needing to be approved by race founder and director Jim Anderson before receiving an invitation to compete.

"The first time I came here was in 1983 and I wanted to do this swim," said Heltzel, a standout swimmer at Stanford. "Jim didn’t know who I was. I had one day to turn in my entry and I hand-carried it to his house. It was like going to see the Wizard of Oz. I kept thinking, ‘I hope I get accepted.’

"I was pretty excited when I got my invitation."

Heltzel, another recognized pioneer in the sport, finished fourth overall in his first outing. He won his first in 1985 and his 12th in 2011, claiming his age group title every year when he wasn’t the overall champion.

His record in 1989 (1 hour, 26 minutes, 55 seconds) was reset a year later by world open water champion Greg Slippert of Canada (1:24:44). Heltzel’s 1989 time remains second-best all-time.

Anderson has only canceled the race once (in 2007 due to his health issues). He also has only denied one application: Mickey Campaniello.

"If I had known who he was other than he was a runner, I would have let him swim," Anderson said of the well-known Hawaii marathon runner. "He was super fit and it wouldn’t have been a problem for him. We all have a good time still talking about that."

However, safety is primary for Anderson. Swimmers have to provide a resume of sorts, showing they are capable of the distance, known as the Double Waikiki Roughwater Swim.

Swimmers also are required to provide an escort on a non-motorized water craft such as a kayak or surfboard. The escorts must themselves be in excellent condition with strong water knowledge; they are allowed to carry nourishment for the swimmers.

"The escorts are the unsung heroes," Heltzel said. "This swim is absolutely my favorite swim in all the world and it’s doable for pretty much anyone who sets their mind to it. Getting escorted the whole way makes you feel more comfortable, especially if you’re new to the ballgame.

"There’s been a couple of occasions where it’s gotten pretty nasty out there and the swimmers have had to leave some of their escorts behind who couldn’t keep up."

Earlier this year the event was one of the first to be sanctioned by the World Open Water Swimming Association. It recognizes that the race promotes the sport and does so in a safe manner in keeping with the international rules and regulations.

And it’s done in the best waters on the planet, Anderson said

"No question in my mind that, as (TV meteorologist) Guy Hagi says, we have the best weather on the planet AND the best waters," he said. "One of our Italian competitors described it as a living, breathing thing. Most of the Olympic events are done on lakes, in calm waters. Here, we get whatever Mother Nature wants.

"It’s a different swim going down and coming back. It’s the only event we have where navigation plays a big role."

That the race is held in December is not to make it Hawaii’s version of a polar bear swim. It was done so, according to Anderson, to fill that gap between the traditional end of swimming season — the Labor Day Roughwater Swim — and the beginning in April.

"Putting it in December, there was another reason to swim and workout," he said. "It changed the whole swimming community."

NOTE: Anderson will be inducted into the International Marathon Swimming Hall of Fame some time next year. The IMSHOF has not decided when and where it will hold the induction ceremonies, with Spain, Scotland and Hawaii the three sites mentioned.