We were once re-routed, too. Based on the weather forecasts, I was pretty sure that we were going to be re-routed, but we didn't know for sure until we were actually on board. This was in September of 2000. When we were boarding, all we knew is that we were stopping at Key West on Sunday (this was an eastern trip, before the western route began). I knew that a previous eastern had gone to Key West and Cozumel, but there was also a storm off the Honduran coast, so I knew Cozumel was probably out of the question.
The original plan was to go to Key West and then see about the weather. That was as much as they'd tell us while we were boarding. There was talk of Nassau and Charleston, SC, too. Later in the afternoon, it looked like we were getting a stop in Nassau and an extra stop at
Castaway Cay. We even booked an excursion for Nassau.
At the opening night show, the Captain announced that the storm in the east had turned south and had downgraded to a tropical depression. He said that after spending a day in Key West that they would assess the latest weather reports, and that we might still go to St. Thomas. As we were pulling out of Key West, he announced that we were in fact going to St. Thomas, rather than Nassau. Our itinerary ended up looking like this:
Sat - Depart
Sun - Key West
Mon - at sea
Tues - at sea
Wed - St. Thomas
Thu - at sea
Fri - Castaway Cay
I guess this is just a long-winded way of telling you that if the trip is going to be diverted, that you'll know as soon as they do, which may not be very far in advance.
This was only one trip during hurricane season. We've been on several others during this time of year and had no problems. I like to sail at this time of year because the weather is still very warm and the prices are usually lower. I just go with the frame of mind that a diversion is a possibility and prepare to adapt to it.