There are no statistics on it, but they'll do whatever it takes to avoid a hurricane or tropical storm. Sometimes ports are cancelled. Other times, based on storm track, they will reverse the itinerary and still stop at all the ports. And then they can change the itinerary entirely. This happened to us on the Century in 1996. Supposed to be an eastern Caribbean. Hurricane developed there, and so our cruise suddenly became a western Caribbean as we arrived at the pier.