Hawaii's weather stays pretty consistent all year round (warm and tropical!). On average the daily temperatures will range between the 70's and 80's, then dropping about 10° F during the night, which is way many people flock to Hawaii during the winter season on the mainland.
How many seasons does Kauai have?
There are basically two seasons in Hawaii - summer and not Summer (just kidding... sorta). They are Summer and Winter.
Kau (Summer) runs from May to October and Hooilo (Winter) runs from November to April. During Winter months expect a higher chance of rain, however, no matter where the rain clouds are you are bound to find a sunny spot along Kauai's coast. If you are coming from the snow (burr), our chilly 60° weather will probably feel like summer to you, however, with the higher probability of rain and heavier makai winds (cold mountain breeze) we suggest that you also pack a light jacket with your island wear. The map below shows the average rain fall for Kaua'i during the Winter months. Poipu receives less rain than most of the island.
Giambelluca, T.W., Q. Chen, A.G. Frazier, J.P. Price, Y.-L. Chen, P.-S. Chu, J.K. Eischeid, and D.M. Delparte, 2013: Online Rainfall Atlas of Hawai‘i. Bull. Amer. Meteor. Soc. 94, 313-316, doi: 10.1175/BAMS-D-11-00228
What are the water temperatures during the winter season in Kauai?
The ocean temperatures in Hawaii are also pleasant all year round. During summer the water is warm and cozy at about 75° F and dips only a few degrees during the winter. The warm pacific waters also bring our friends from the sea. Approximately 10,000 Humpback Whales will travel thousands of miles to breed, give birth, and nurse their young in Hawaii's tropical waters. Peak season for Whale Watching is January through March.
Surfers look forward to the winter months because the winter season brings big wave conditions to the North and West shores of the islands. Winter in Kauai is a surfers haven to say the least. Even if you are not a surfer it is quite the experience to watch 20-30 foot waves barrel toward the shore.
Luckily for us in the south, when the ocean is rough and tough on the north and west shores, Poipu beaches stay calm and serene. There are also two lifeguard stations manned 7 days a week at Poipu Beach. Keeping the most popular south shore beach safe.