To add to what Sandy said, note that since it does rain nearly every day, the forecast almost always call for rain. So just because the forecast calls out rain, doesn't mean it will. The only time when rain tends to last all day in the Caribbean is when there is a tropical storm. Other than that... it normaly doesn't rain for long.
Go and have fun...
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013