Well to put it bluntly its the caribbean in the summer. Its hit or miss, especially in september. Weather will still be very hot, and the water nice and warm. There is just a greater risk of bad weather. You could have a great cruise not a drop of rain (rare chance of not a drop since there are always lots of hit or miss showers and downpours) Even if there is a hurricane they will just change the itinerary far away from the hurricane.