Yes it would be great to dive Tunnels, but like you mentioned the conditions are not good in Dec.
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Just got home from Kauai. Did 3 days of diving with Aquatic adventures, HIGHLY RECOMMENDED! Dive Koloa landing for sure, it was a great critter dive, Shawn was my DM and he was fantastic for finding the small critters most would just swim by. Sadly though by December it will take a massive stroke of luck to dive Tunnels, too bad, that was an AMAZING dive, probably the best shore dive I have ever done. I also dove with Fathom 5 for a 3 tank boat dive, they did a good job too. Personally I'd avoid Seasport, they run what looked to me to be your basic cattle boat.