Previous writer pretty much has it down, however , keep in mind they will hold a ship for an hour or two, but not for a day or two. We travel a day in advance during any season that weather can be an issue. Buy travel Insurance. It will give you some peace of mind if your stuck and not going to make the ship to know that at least you will be reimbursed for the cost of the trip.
My TA told me that if you buy the travel insurance it only helps if you bought the air through the cruiseline. I'm not certain if this is consistent across all cruiselines, but I thought I'd mention it.
I'm concerned for the same reason. We are scheduled to arrive 5 hours early. At 1st I thought that was plenty of time, but now I'm hearing that it's really risky. We called our airline (US Airways) and asked how much it costs to change flights. It will cost $100 per person to change the flight which is about the cost of travel insurance, then we'd have to pay for a hotel near the port. So we decided to stick with our plans, watch the weather before and decide if there's going to be a need to change.
We traveled last March and had a problem not from the weather but the fact that the plane did not come in from the previous airport. I got up early the day of the flight and checked the web page. It said that the flight was canceled, so I called the airline, they said that all flights from our closest airport were booked. We ended up catching a flight from Chattanooga. I live in Knoxville TN, about an hours drive. We ended up getting to the ship on time, but others who didn't check on the flight showed up at the airport and had to take a much later flight. They missed the ship and had to go to the first port of call to wait on the ship. Fortunate for them, since the airline screwed up, the airline had to pay the expenses. The only other problem we had was that some of our luggage was delayed. it too made it to the first POC. The cruise line and the airline both paid for clothes to wear and the cost of the damaged luggage. I could have claimed it on insurance too but I didn't.
I have purchased insurance and never had to use it. Better to have it and not use it than not to and need it. I will not do major traveling without the insurance.