First, we like warm water. And Hawaii does not have the warmest of tropical waters, so going when it is not chilly is nice. The water temperature in Hawaii ranges from about 74°F in the winter to about 82°F at the end of the summer. So in the late summer that is not bad, and we can stay in the water for an hour or two, wearing a regular rash guard on top. In winter though, it is a bit chilly, particularly in the mornings, and so we like to wear a thin neoprene wet suit top. So we enjoy summer more.