Ok here I go again in unknown territory.

I have booked us, and some brand new cruiser friends, on the Liberty for August 15th 7 day cruise. The itinerary is; Half Moon Cay, St Thomas,
PR, Grand Turk plus of course the sea days. I did get trip insurance, but would be awful if we got rain everyday and couldn't go to the beach (real reason for cruise). What are the chances of that? I remember the caribbean last year in February rained in the morning in St. Thomas, cleared up in the afternoon, but the water was cold. We have never came east way in the summer months. Any ideas on what to expect? The water should be warm right?