Need the low down on Kauai

[AquamanKauai]

I'm hardly a Kauai expert, but March for Tunnels is very 'sporty'. You're very likely to get big surf
Ha'Ena Bay (Cannons/Tunnels) Surf and Swell Size and Direction
You're likely to find shore dives to the south (Poipu Beach) to have poor visibility that time of the year too. . .

The west side of the island is more sheltered from the prevailing winds in March , boat dives out of Port Allen (Bubbles Below) or Waimea (Kohala Divers) may be your best bets

Spring is actually often wonderfully clear and calm diving on the south shore. Some of the best late season whale encounters I've had over the past 15 years and the beginning of some pretty awesome fish spawning events. With such a large variety of dive sites (25 approx) you're likely to find great vis. Any "mother nature" related events that would cause lower vis would impact the entire southern area all the way down through Port Allen.

Cheers