We fly to HNL every Christmas, albeit from the east coast, and it never gets any lower priced. We book F (and a few seats in Y), and by early May, F is completely sold out for most one-stop (and our one non-stop) flights on peak days. The hardest dates to book are 12/26 and 1/1, so if you are determined to fly on 12/26, I would book as soon as possible. Also, try to lock in your accomodations early, they can always be changed later if prices drop or you change your mind.
Robin