Its my understanding the water is a tolerable temperature year-round. But I think the bigger concern would be the size of the waves that time of year. I know in some places, the ocean waves can be impacted by winter storms. When we were in Hawaii in September, which is hurricane season, and the waves were quite high even though there were no storms in the vicinity. We found it difficult to swim the ocean, with the exception of the lagoon at Aulani.