If you booked through a travel agent (which is recommended), the agency will be notified by Princess and the agent SHOULD notify you. If you booked independently, Princess should notify you. If you booked through an online source - good luck!
We were on the Caribbean Princess last week, and the Captain sent around notices the first night that we'd be starting our itinerary in reverse order and then they would re-evaluate the itinerary the next day. After that, he decided to switch from Eastern Caribbean to Western. It was fine with us, and we had perfect weather all week, despite Hurricane Rita trailing us by about 450 miles every step of the way.