St. Thomas is located in the Caribbean, and it can get typically and tropically hot during summer months July to September. Of course "hot' is relative to many people because it is often cooler in that part of the Tropics than Stateside during the same time, with the island's heat index tending to be in the low 90's because of the prevailing breezes and winds. It really depends on what you're used to.
Island visitors come year round, but November thru April are the busiest months, coinciding with colder temperatures Stateside and in Europe. June is traditionally a busy month for brides; the temperatures still average moderately in the low 80's.
If you are at sea level, close to the beaches, or higher elevations, and you have an easterly orientation, you will tend to have a nice cooling breeze where you may not even need air conditioning. Otherwise the apparent temperatures (heat index) will increase with reduced breezes or the occasional shift in wind direction. Overall air temperatures range from the 70's at night to low 90's year round.
The Virgin Islands does not have a rainy season per se, but September, October and early November have statistically more rainfall, which coincides with the Atlantic hurricane season in full swing. A good time of year not to visit this part of the world for most people, though contrarians and happy campers come and go, dodging the odds, and enjoying the islands with less crowds.
Atlantic hurricane season runs from June 1st to November 30th with the highest occurrences of storms in August and September, particularly mid-September. The season affects many countries and islands in this hemisphere.
Rainy months does not mean that there is continuous rainfall every day all month long, in fact most daily rainfall reports are below a tenth of an inch. Rain showers are often short and typically occur early in the morning or at night. On a truly rainy day, it will rain on and off for the entire day. All day downpours over numerous days are not common. The driest months are typically December thru March, which is another reason that time of year is popular with island visitors.
During extended dry months without the occasional rain shower, the island may momentarily lose its typical robust green tropical look, and "brown out". That's because the island is volcanic in origin, has almost no topsoil, and the plants and trees have very shallow root systems. They will protect themselves from no rain by going dormant, but are incredibly quick to respond to rain and quickly bounce back with a "spring green" look and freshness in the air.
Water temperatures in the Virgin Islands do not change greatly from summer to winter, however the 4 or 5 degree change is noticeable to those acclimated to consistently warm tropical weather. In the summer months the water temperature is about 83 degrees and in the winter about 79 degrees.
Overall, the weather reports tend to be the same from day to day thru out the year, and boring to listen to. Sunny with occasional clouds, and a slight chance of rain. The occasional exception, like anywhere else, gives everyone something to talk about. Locals basically look to what flowers are blooming, how green the vegetation is, and how many island visitors are there, to tell what season of the year it is.