Just as the surf on Oahu’s North Shore promises to build this week, so has the interest in stand up paddling internationally. The Stand Up World Tour is proof of the growth in what was considered a fringe sport.

It has become bigger, adding four stops around the world. It is becoming epic, like the hoped-for conditions at the Sunset Beach Pro. The first stop of the world tour begins its holding period this morning with the potential to get in a full day of trials.

Returning to defend his Sunset Beach title is 18-year-old Kai Lenny of Maui, the reigning world champion. He won this event last year — the opener of the inaugural world tour — as a wild-card entry.

"The swells are coming up, and it’s supposed to be big," Lenny said. "The bigger it is, the more comfortable I am. The conditions look to be similar to last year, maybe cleaner. That it could be epic out there has everyone stoked."

Lenny grew up surfing, windsurfing and kitesurfing on Maui’s North Shore. But when he saw surfing great Laird Hamilton do an SUP downhill run about eight years ago, he said, "Man, I want to do that. And I’m loving it."

Lenny is one of the younger competitors on tour. The ages in this week’s opener range from 13 to more than 50.

"That’s the greatest thing about the sport," said 40-year-old Kamaki Worthington, a longtime crew member of the sailing canoe Hokulea. "It allows everyone to be a part of it. Although I did feel weird at Sunset last year when standing on the podium. I was third and the winner (Lenny) could have been my son."

Besides the Sunset Pro and the finale at Honoli’i on the Big Island, the tour returns to Ibiraquera, Brazil; Sapinus, Tahiti; and Anglet, France. Added this year are stops in Brittany, France; Punta de Lobos, Chile; Cardiff, Calif.; and Victoria, Australia.

In the current world rankings, Hawaii dominates with five in the top 10: Lenny at No. 1, Robin Johnson No. 4, Duane DeSoto No. 5 and Ikaika Kawaii No. 10. But Frenchmen Peyo Lizarazu and Antoine Delpero rank 2-3 and Tahitians Arsene Harehoe sixth and Tama Audbert ninth. Australian Dave Muir ranks eighth.

The Sunset Pro opens with a 40-man trial, with the top moving on to a 48-man main draw. Waterman League tour director and CEO Tristan Boxford said the conditions may allow for the event to be completed as early as Thursday.

The decision to run the competition will be made at 7:30 a.m. daily, with heats starting at 8 a.m. The webcast on OC 16 begins at 7:30 a.m. on days with events.

"I’m looking forward to this second year," said Kainoa Hauanio, who grew up on the Big Island but now lives on the North Shore. "The waves were fun today and hope they increase for tomorrow.

"What started with the beach boys right here (in Waikiki) has progressed to a world sport. I’m not surprised it has grown."