It depends on where the hurricane is and where it is predicted to go. On one cruise a couple years ago, the captain changed our ports of call in order to keep the ship away from the area where the hurricane was. In 2004, each cruise that was "bothered" by the hurricanes was different...depending on the hurricane.
DCL has the option of using a couple of other ports if Port Canaveral is closed. They can cruise to another area of the ocean. Worst case, they can cancel a cruise. They will let you know what they plan as soon as they can make plans...which is usually only a day or 2 before your cruise is scheduled to depart.
For Jeane, our 7 day cruise became a 4 day cruise leaving out of Ft. Lauderdale. DCL did offer us the chance to cancel our cruise with a full refund (no good, since we were already at WDW booked separately), 40% off the cruise fare portion of our ticket, an onboard credit, and a 25% discount on a future cruise. Bottom line, we were treated fairly by DCL. They don't (YET) control the weather!
The other side of the story is that we have cruised in September 5 times. 2004 was the only time our cruise was really impacted. I'd do it again...in fact, I'll be on the Magic in September, 2005. I would suggest you would buy
travel insurance.