Aloha from the island,
Excited for you and your upcoming trip to Kauai! I think you'll find the differences between diving on the Big Island and Kauai pretty exciting. The ecology is quite different and many critters rare to one - are quite common on the other. Kona certainly boasts some unreal visibility with her deep water just off shore along with some great big critter encounters. Flame Angels, male Whitleys boxfish, and Garden eels for example are seen with some frequency on the Big Island and "almost" unheard of here on Kauai. While my Big Island knowledge came from one years experience on the Kona Aggressor, I can help you with extensive information on diving Kauai as it's been my home for the better part of 15 years.
The best diving in my opinion is in the Poipu area (at least during the winter months). Fantastic sites like Sheraton Caverns (#1 requested dive on the island), Turtle Bluffs (Whitetip reef sharks, octopus, large morays), and Brenneckes Ledge (Black corals, numerous inverts including great nudi's) are just minutes away.
The must must must do shore dive is Koloa Landing! I simply love this dive with all it's fantastic critters. Turtles, octopus, endemic Green Lionfish, nudibranchs, Devil and Leaf Scorpions, rare Freckled snake eels, and currently 3 species of frogfish! It's a shallow and relatively protected bay in the 15-50ft range with average depths around 30-35. Oh, and I carelessly forgot to mention the site has the AMAZING Dragon Morays as well! Access is easy and many divers do multiple days of guided dives there due to its' ease, critter intensive nature, and long bottom times.
Kauai diving on the whole is a little more rugged that diving the overly protected Kona Coast and dive planning should be done a little more carefully in my opinion. Perhaps better stated I would say that there can be great dividends paid to choosing dive sites, dive times and days with a little guidance. That can be done easily when you're here with the right assistance and I'd be happy to help with that further.
Kauai is the only island where the primary diving is not on the leeward side. This means that you are out in the wind all the time. At times the winds are light or at least moderate and morning boat dives are changed little. Afternoons can however become quite limited - as can mornings when the winds are 15-20+. If mother nature is offering some options it's best to choose boat days that are less than 20mph winds. The trade wind pattern is NE is flow and peaks generally in the early afternoon. Light and variable winds or winds from the North make diving ideal though those days aren't as commonly experience.
Dec is also an unreal time to be here to experience the Humpback Whales around Kauai. You'll likely see them daily and get to hear the singing males on you dives.
Well, I hope this basic information helps you out just a little. While I personally guide now with Fathom Five I can help you with information as it pertains to any of the shops here. Additionally if I can help you with information that's non-diving - I'm happy to do that as well. I frequently mail out guide books for people to borrow while planning there trip if that would help. Otherwise feel free to send me a personal message with any questions you may have.
Have a fantastic weekend and happy dive planning
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