Last week we were on the Fantasy on this same Eastern Cruise.
Cruising Down to the Caribbean and Back again, the ship was really rocking and rolling!!! Bring your motion sickness meds and use them.
Seas were light (only about 6 feet), but the wind across the deck was brutal ... usually mid to upper 40mph, reaching into the 50's. "down" on deck 11 (pool) the wind was not much of an issue. Deck 13 forward (adults only / Satellite falls) depending upon the side of the ship you were walking on, was very windy, BUT once you made it up to the wind screen area (covered), it was actually quite pleasant. we spent a lot of time up there.
We had an excursion in Tortola and it was raining hard in the morning, then let up before we left the ship.
DCL was handing out rain ponchos for free (WDW logo - at $15 a pop, we "made 60 bucks

). When we got to the Baths on Virgin Gorda, it started raining HARD again. 10 minutes later no more rain for the rest of the day and mostly blue skys with a few puffy white clouds.
Back at the ship in the afternoon it was in the low 80's and just perfect - more time spent up on deck 13.
St. Thomas - NO rain at all, just the blue sky and the white fluffy clouds. We did not have an excursion and decided to stay on-board up on deck 13 again for the day -- it was heavenly.
The cruise back up north - more winds and a few sprinkles - yep, deck 13 forward was pretty nice all day.
Castaway Cay - now this was a different story. only about 70 degrees, windy and rainy. Cold outside. We stayed inside the ship that day. With the wind, I was surprised that we were able to dock. It would have been better if we didn't - then the cruise staff would have been able to provide more activities on-board. DCL added more showings of the New Star Wars and Good Dinosaur (awesome) movies and a few additional activities on-board. AND the Bahama government allowed DCL to open Shutters and the stores while docked because the weather was so miserable.
Castaway Excursions: any excursion where an outside vendor had to come over to CC from Abaco were cancelled due to safety concerns. Things booked that totally resided on the island: Snorkeling, Biking, Stingray Encounter, Cabanas, massages went on as "scheduled". Disney will NOT refund your money if the excursion goes, even if the weather is bad. They will cancel for safety reasons. IF DCL cancels, they refund you fees for excursions that you booked through DCL. Outside vendors (in any port) cancellation policy varies by vendor.
any other questions???