Carnival Fascination set sail from Jacksonville for Bahamas while Hurricane Joaquin was still beating the islands.
It’s in your contract. If the weather is bad the ship can go somewhere else where the weather is nicer. This event can be one of the chief reasons to purchase a shore excursion through the ship, as cancelations will, in almost all cases, be refunded or credited for a different excursion. Shore excursions can cost as much as half as those booked through the cruise line and a lot of scrutiny of the excursions is claimed by the ship. In fact, the ship staff will work hard to arrange alternative tours at a replacement ports. The little fine print in your contract that no one bothers to read covers the cruise line for bad weather forcing port changes.
Check Cruise Critic Boards for the cruise on which you are booked for others needing to add one or two more with their small van tours in a port.