Went on a Southern Carrib. cruise (St. Thomas, St. John, St Kitts, St. Barts, Barbados, St. Lucia) the week of December. Water was too cold to swim except in St. Barts and Barbados (most southern islands). Virgin island water were cold and rough, compared to all my trips there in May-July. Won't go in winter again. The tours are wonderful on all eastern island itineraries, so don't have to swim if you choose not to!