It's become the biggest local concert in Honolulu — a summertime party with performers you like to hear and see.

It's the KCCN FM 100 Birthday Bash XV, tonight and Saturday at the Waikiki Shell.

Like a mammoth birthday cake, the event boasts ingredients that please the senses, trigger camaraderie in the audience and provide sweet thoughts for days. You can indulge tonight, and return again Saturday for a second serving, if you're so inclined.

Why go? Why is it so hot? Here are 15 reasons:

1. Two nights of powerhouse music. The one-nighter was expanded three years ago, reflecting the popularity of the music and acts available.

Tonight's slate: Fiji, Bruddah Waltah, Ho'aikane, 'Ekolu, Koauka, B.E.T., One Groove, Kekai Boyz, and Malino.

Saturday's roster: Kapena, Natural Vibrations, Sean Na'auao with Bruddah Waltah; Ho'onu'a, The Brothers Cazimero, Keahiwai, Inoa'ole, the Opihi Pickers, and Kamaikaiwa.

2. The longevity of Kapena. OK, the membership has since changed, but Kelly "Boy" DeLima and his combo are the only act to perform in the previous 14 Bashes, so the group wins the nod for a frequent player award.

Last year's appearance featured a remarkable nonstop set of the 23 songs Kapena has shared in the history of the event, one tune segueing into another, for a breakneck medley lasting 25 minutes. Not surprisingly, that brought down the house.

3. A chance to check out the growth of several acts that played in the first Bash, and are still around, pleasing audiences. Besides Kapena, these troupers are the Mana'o Company, Ho'aikane and Bruddah Waltah.

4. Kapena DeLima, son of Kelly "Boy" DeLima. Kapena was only 1 when the series was launched; he's with his dad's group now, as full-time keyboardist, but also played in the past two shows as a member of Next Generation.

5. Early arrivals Saturday can ogle the Venus Legs pre-show entertainment, starting at 5:15 p.m., and sponsored by Gillette. (Sorry, dudes — this is a women's participation thing.) Contestants were chosen in advance.

6. The big video screen is backthis year. If you're sitting in the cheap grass seats, a time zone away from the main stage, be happy about this. It's not exactly a Jumbotron, but the oversized LED images will let you to see the performers without using binoculars.

7. The homecoming of Danny Kennedy, one-time Mana'o Company member, in a reunion with group co-founder Sean Na'auao.

Kennedy and Na'auao, along with other musicians, were pillars of Mana'o, but the group disbanded — in fact, there was a rift between Na'auao and Kennedy. Kennedy went on to pen one of the reorganized group's biggest hits, "Aloha," but a drug-dealing charge sent him to prison, and that ultimately led to the dissolution of the act. Meantime, Na'auao launched a successful solo career.

Long story short: Kennedy has served his time, returned to the Islands three months ago to participate in a halfway house program, but needed a sponsor to return to the stage. Na'auao buried the hatchet and agreed to sponsor Kennedy. Kennedy will perform in Na'auao's group in a supporting role that also is a homecoming celebration (only on Saturday's slate).

8. Return of the Island boys. Though from the Mainland, One Groove, performing tonight, includes ex-pats galore — Chris Lavatai, Kris Kanoho, Jose Dangtayan, Hini Galuteria, Keone Catian, Chris Canubida and Brent Nishikawa — who are the reigning reggae act in the Bay Area. All have Island ties; and yes, Galuteria's dad is Brickwood Galuteria.

9. Dining under the stars. You can bring your supper or buy from concession stands offering food and drink. Most folks go as a large party, spread the mats, dine together, and enjoy each other's company as well as the parade of performers on stage. Reminder: Large coolers and from-home alcohol are not allowed.

10. Reggae and Jawaiian galore. Most everyone on the slate tonight and tomorrow will do something with that Jamaican beat. Wonder if The Brothers Cazimero, largely known for their Hawaiiana, will get into the groove, too, Saturday night?

11. An international crowd. Besides the dominant local contingent, many visitors plan their trips to coincide with the Bash. Countries frequently represented: England, Croatia, Australia.

12. Many "extras." Performers are encouraged to add an element of surprise to the evening fun; hula halau and guest musicians have highlighted past programs.

Among the memorable flashbacks: Ho'onu'a joined by the entire Kamehameha Schools marching band drum line; orchids dropping (in the thousands), accompanying a Mana'o Company appearance; Sean Na'auao scooting in on a Harley-Davidson; Kapena releasing doves into the night.

13. Gifts for early arrivals. The first 5,000 through the turnstiles each night will receive an FM 100 Birthday Bash keepsake beach towel that is available only at the concert. You can use it as beach mat, wear it as a makeshift sweater ... or just wait till you hit the beach Sunday. (What, you expected them to hand out 15,000 each evening? Early arrivals always are rewarded; in past seasons, gifts have included a mini FM radio, an auto sunshade and a license plate frame.)

14. A big finale. It's a good plan to stay till the end. Normally, the finale is the frosting on the cake — something wild, something big, something worthy of the Bash.

15. Bargain tickets for early-birds, who gained admission for $15 per show. Lucky you bought early if you scored tickets in time. (The final day of this promotion yielded the highest single-day sales in the history of the Bash.)