JP Kennedy — guitarist, vocalist, and a founding member of The Green — was up against an entertainer’s nightmare.

The Green was on the mainland with one more big sold-out show to play — co-headlining with J Boog and Hot Rain. They’d be back in Hawaii in two, maybe three, days, but his “other half” was due to give birth in a matter of hours.

The more she assured him that it was OK and she’d be fine without him, the more he felt he should be with her.

So, in the middle of the night, Kennedy wrestled with one of the toughest decisions in his life.

“I was thinking it wasn’t cool (to leave) but coming down to it, it was one of my life decisions: ‘Am I going to stay here, or be there when my kid is being born?‘” Kennedy said last Tuesday, relaxing with three other members of the group — Ikaika “‘Kaiks” Antone, Zion Thompson and Brad “BW” Watanabe – in a hidden rehearsal space in Iwilei.

“We don’t miss shows,” Kennedy explained. The members of the band had decided that; they were committed to their performances, and to The Green.

“I woke up ‘Kaiks and Caleb, and I was saying, ‘What should I do?’ They said, ‘You gotta go.’ I was so stoked that the boys were cool with me,” Kennedy said. “I was already expecting someone to be upset. I was already upset myself!”

At the rehearsal space, Thompson also looked back on that day in February, volunteering that he had been last to agree with Kennedy’s decision, but finally told him to go home for the birth, because “family’s more important.”

The band, also a family, proved their commitment to each other in Kennedy’s absence. Playing a major concert one man short was “crazy,” Antone said; but they pulled it off.

“We learn as we go how to deal with certain things. Now that we’re all having kids and families its getting a little more tricky, but as long as communication is solid, we’re gonna be alright.”

“We told him, ‘You gotta be there for your family.’ We did the show without JP. It was awesome — and we facetime’d JP in the hospital during the show.”

“I was so thankful,” Kennedy said.

THE BAND came first in the early years for The Green, Kennedy said.

“Maybe we had girlfriends, but this was our career before we had serious, serious other-halves. That’s why we had the time to travel and do all the touring we did in 2009, 2010 and 2011. … I needed the boys, and I was stoked to be part of the band.”

That commitment to each other — and the willingness to make occasional exceptions for exceptional reasons — are two of reasons that The Green has survived, and has played together for almost nine years without any changes in membership.

At the moment, vocalist Caleb Keolanui is the almost-father of twins that could be born the day of the concert, Thompson said. Keolanui had been at rehearsal, but did not stay for the interview, and no one faulted him for that; on Friday he’ll be on stage at the Shell, come what may.

The members’ commitment to their music has made The Green one of the foremost Hawaii-based reggae groups of their generation. Hawaii will see them Friday when The Green appear as the headliners of the first night of the KCCN FM 100 Birthday Bash at the Waikiki Shell. California-born Samoan-American recording artist J Boog is at the top of the bill on Saturday with another concert lineup.

The two night event is a revival of a tradition that began in 1991 when KCCN FM 100 was promoting what was then called “Jawaiian” music — music arranged around the basic Afro-Caribbean rhythms of Jamaica. When the term “Jawaiian” fell into disfavor, radio station music marketers rebranded the FM 100 format as “island music.”

Jawaiian/island music pioneer “Brudda Walta” Aipolani won the Na Hoku Hanohano Award for best contemporary album in 1991, but the Hawai‘i Academy of Recording Arts didn’t give reggae music its own category until 1999.

THE GREEN got together in 2009, with Antone on keyboards, Kennedy and Thompson playing guitar, Watanabe on bass and Jordan Espinoza on drums. Antone, Kennedy, Keolanui and Thompson share vocal parts.

Their self-titled debut album won the 2011 Hoku award for reggae album of the year.

The Green’s second album, “Ways & Means,” helped build the group’s momentum with its release later in 2011.

The third, “Hawai‘i ’13,” made history three years later, when The Green became the first Hawaii reggae group to win a Hoku for group of the year. The band also won the reggae album category for the second time, and won the public vote for favorite entertainer of the year.

The group’s fourth album, “Marching Orders,” was released last fall. Friday’s show will be Hawaii’s first chance to hear songs from the album performed “live” in the islands.

“We haven’t done a live Hawaii show for the public since the album’s been out,” Thompson said. “This is special because we get to play the new stuff — all the new songs they’re playing on the radio — plus we get to play it in front of the home crowd.”

Headlining a show at the Shell is something the band has always wanted to do, Antone said.

“It’s always awesome to play at the Shell. It’s a great place to show to showcase stuff and present our album, and we definitely want to do something special.”

After headlining the Aloha From Hawaii festival in Hilo and Kona on Hawaii island next weekend and on Maui on May 5, the group will be off to do more touring — perhaps on the mainland, perhaps in New Zealand or Australia.

There are plans for another album — an acoustic retrospective of the The Green’s songs from the first four albums. Thompson says that will “showcase that we all play instruments and where we come from, and a little bit more intimate view of us.”

The Green might also do a Hawaiian album: Band members have been getting together at bassist Watanabe’s house to work on Hawaiian songs. “We’re talking about maybe putting out a side project of Hawaiian music,” Kennedy said.

“It’s something I always wanted to do,” Watanabe said. “It’s something I grew up playing and listening to my whole life, so its something we’re brainstorming.”

“Reggae is the thing that brought us together,” Kennedy continued, summing up. “That’s always a constant. We’re always working on that first, but we have so many other influences that its natural for other little project ideas to come up. We’re just always jamming and working on new stuff.

“It’s just a constant battle to get people to listen to us, to get people to pay attention to Hawaii,” Kennedy said. “It’s a non-stop battle, but we think we’re winning.”