The weather in December is wonderful. The rains will have ended (except an occasional shower) the water is clear. Everything is open. Dec-April is "high" season because the weather is so beautiful. However, we have visited in June-July too and have had great weather. Sept - mid Nov is more iffy. If we are going down during those months we pay close attention to the weather.
Cruise ship crowds increase during "high season". This complicates driving on St Thomas. St John and Water Island are less affected by the cruise ships.
Enjoy!
