Haikou Temperature in January

Well, the average temperature will be about 75 F during mid January. And the water temperature may range from 60 F to 65 F. The climate will be warm and comfortable. Generally speaking, you can fully enjoy the swimming. However, in order to avoid changes of weather, you are still suggested to watch the forecast before going there.
For beaches to swim, you are advised to go to Sanya, where there are many great beaches, like Sanya Bay, Asian Dragon Bay.