We were extremely lucky in that we only had one day where the weather was "Icelandic" (windy, rainy, cold). It was in the 50s and 60s the other days with lots of sun and calm seas. You can't count on that delightful weather, however. I would bring a rain jacket, parka with hood, waterproof hiking shoes/sneakers, waterproof pants, fleece shirt or jacket, sweater, wool socks, warm hat and gloves. I wore fleece-lined leggings frequently. Bring a bathing suit for the hot tub, sauna, and steam bath. Dressing in layers is the best way to go. You will love the cruise. Wishing you smooth sailing.