You are sailing there during the hurricane season so although it will be quite hot there could also be days when it may be cloudy with typical Caribbean 30 minute downpours on the islands. Cruise ships are able to avoid the hurricane areas but it can mean you lose out on ports of call for safety reasons. I don't know how far they go out of their way to avoid bad weather so can't comment on how rough and windy it may be.
Thank you! Looks like I'll be needing the seasick tablets then. Have you been?
I've been quite a few times but have always flown out there and it's been between late November and April. I'm sure you will have a good time. The islands are amazingly different from one another but very enjoyable. It's quite a while since I was last on Oriana but it's my favourite ship (and good in rough seas!).