Sacramento's ties to Hawaii go way back – back to the time of John Sutter, who visited the islands and returned to the mainland with Hawaiian workers.

Sacramento's annual Pacific Rim Festival remains popular, and there are a number of halaus, or hula schools, in the region.

That only partly explains the appeal of Hapa, the two-man slack-key group headed by a white guy, New Jersey native Barry Flanagan.

Hapa, dubbed "the most successful Hawaiian music group in recent history" by the New York Times, plays this week at Harlow's. It sold out the 250-seat venue last year and has been playing to packed houses on the mainland for years.

The group's music was featured on this season's "Hawaii Five-0" and in the recent romantic comedy "Just Go With It," with Adam Sandler, Jennifer Aniston and Nicole Kidman.

All of this is good news for Flanagan, a haole Irish Catholic who left New Jersey 30 years ago, immersed himself in Hawaiian culture and slack-key (open-tuning) guitar technique, and went on to create music that is Hawaiian with a twist of jazz and world beat.

Interest in Hawaiian music is deepening as groups like Hapa continue to bring slack key to new territories.

"Don Ho's advice to me 20 years ago was not to play the big cities with Hapa, but places where no one has gone," says Flanagan. Once experienced, the music generates what Flanagan describes as "a Hawaii state of mind" – meaning instant relaxation. "The blood pressure goes down and the white blood cells go up."

Hawaiian culture has also gotten a popularity boost thanks to President Barack Obama, who was born and grew up in Hawaii and returns regularly to his childhood home.

Flanagan is the group's songwriter and lead musician. He's had his Washburn Monterey guitar since his busboy days as a slack-key student in Hawaii, drawn to the music scene by the works of masters like Ry Cooder, who played with the Rolling Stones, and Hawaiian master Gabby Pahinui.

Flanagan's Hawaiian mentors told the young man to focus on learning the slack tuning and then add his own style. Flanagan says he's stayed largely true to that advice – always ensuring that the traditional chants and music he weaves into Hapa's offerings reflect Hawaiian language and culture.

"There's always been room for haoles in Hawaiian music," says Flanagan, speaking via telephone from Canada, where Hapa's tour included stops in the San Juan Islands – a place where, he says, no Hawaiian group had played before. "There have always been outsiders bringing influences to Hawaiian music to make it contemporary."

"Hawaiian music is not static, it keeps changing," agreed Pat Toyama, who directs the Sacramento-based nonprofit Ohana Dance Group. Even slack-key guitar, which has become a sort of soundtrack of Hawaii, was added to the Hawaiian musical repertoire by the Spanish-speaking Mexican cowboys, the paniolos, in the 19th century. Flanagan "is very well-respected in the (Hawaiian) community," added Toyama. "He has brought beautiful music to the forefront that is accepted by everyone."

Hapa takes its name from the Hawaiian word "half" – referring to a person of mixed race. For eight years, the Hawaiian part of the duo was electric bassist Nathan Aweau, who left the band a few months ago to launch a solo career. Replacing Aweau is Ron Kuala'au, a singer and slack-key guitarist Flanagan describes as a major influence in developing Hapa's signature sound. Flanagan says the two are working together on a new album featuring ukuleles that is about a year away from release.

Hula will accompany a part of Hapa's performance at Harlow's. Missing from the concert is veteran Hawaiian chanter Charles Ka'upu Jr., who died in Maui last week. Flanagan said Hapa will keep an empty chair on stage at Harlow's, and fans of Ka'upu are invited to bring leis and flowers to honor his memory.

HAPA

What: This two-man Hawaiian slack-key group is made up of Barry Flanagan and Ron Kuala'au.

When: 7 p.m. Thursday

Where: Harlow's, 2708 J St., Sacramento

Cost: $25 advance; $30 day of show

Information: (916) 441-4693, harlows.com

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