We've had low temps into the low 50's to mid 60's here on the north shore of Kaua'i over the last month and a half. Rain, should also be considered during this time of year for all Hawaiian Islands. It's our *winter months*, no snow, unless your at the higher elevations on the Big Island of Hawaii at 10,000+ feet on Mauna Kea Or Mauna Loa. Due to the prevailing NE trade winds, temps can be pushed to lower temperatures during the evening periods. A light fleece and a rain jacket is always a +, for the *just in case* and will still keep your weight within the *normal range* of things.
Check Local Weather Forecasts & Surf Reports for Ocean conditions.
Enjoy your visit!