The St John weather and surrounding islands such as St Thomas, experience 80 degree plus days and nights in the 70s for the entire year. Unlike Cancun weather, where it can occasionally be cool in December and January, the Virgin Islands have wonderfully warm days and evenings. The weather between the islands does not vary that much and a forecast for St Thomas is as good as St John. Just because the St John weather forecast predicts rain, does not mean that the day will be a wash out.
Overall the best weather months are February and March where the Virgin Islands see the least clouds and rain, less wind and humidity and abundant sunshine. Starting in June, temperatures, humidity levels and rainfall start increasing and peak in September.
I have visited St John three times, twice in early December and once in February. While both December trips were wonderful, there were more clouds and rain but we still had plenty of sunshine. February was absolutely beautiful with bright blue skies, light winds and no rain at all making this time of the year my favorite time to visit.
As with all other tropical locations, the St John weather forecasts can be hit and miss and often times are very pessimistic. The weather is usually much better than predicted. Even when it rains, showers quickly come and go with the intense Caribbean sunshine returning quickly.
Monthly average high temperatures only vary by about 5 degrees throughout the year, ranging from 85 to 90 degress. Low temperatures average around the mid 70s.
Rainfall, wind and sunshine are not affected as much by island topography as compared to Maui because the tallest mountain is only about 1200 feet. Micro-climates do not exist in St John because the island is small and only has rolling hills. There are no dry or wet sides of the islands. As with any tropical location it can be raining in one location and sunny a mile away. When it does rain, it is generally a cool, soothing shower that refreshes and prepares you for more sun.
The most rain occurs between August and November and the least in February and March. Summers are humid as the daytime highs hit 90 degrees or above and the area is prone to the affects of hurricanes that pass nearby between June and November.
The ocean water temperature is perfect, not too hot and never cold. It is always refreshing and takes the edge off of the intense sun and humidity.