However, if you're not actually in Hawai'i (as you can see, the Hawaiians prefer we spell it that way), where King Kamehameha Day is an official state holiday, you may be casting about for something else to celebrate today.
One possible alternative is Corn on the Cob Day. A micro-mini-holidayette if ever there was one, one of the Usual Suspects I consulted in the preparation of this post suggested that the dental floss industry is the day's official sponsor. Our crack research staff was, of course, unable to verify or refute this claim.
On the other hand, we're still some way away from even the Fourth of July (when corn, traditionally, needs be only knee-high).
You may therefore wish to defer celebrating Corn on the Cob Day until fresh, locally-grown sweet corn is available in your locality.
History may provide some additional alternatives to King Kamehameha Day.
Today happens to be the 503rd anniversary of the marriage of King Henry VIII of England and Catherine of Aragon (that's Kate, above). Of course, that one didn't exactly work out.
According to the calculations of Eratosthenes of Cyrene (276-194 B.C.), today is also the anniversary of the sacking of Troy. Yes, on this day in 1184 B.C., the Greeks finished horsing around and ended the Trojan War. Worthy of celebration if one was rooting for Team Agamemnon -- perhaps not so much if one favored Team Priam.