In the event -- and NCL is covering all the bases here -- that a cruise is actually cancelled as a result of inclement winter weather, NCL will not only provide a full cruise credit but also will pay any "reasonable incidental expenses" passengers incur in rearranging their travel plans.
It must be noted, however, that travelers are still -- good weather or bad -- responsible for getting themselves to and from the ship. NCL is not responsible for missed cruises because of inclement weather delay (need we say the words: travel insurance?).
Norwegian Dawn's winter cruise schedule includes its flagship seven-night Bahamas itineraries (which also call at Miami and Port Canaveral) along with a sprinkling of 10- and 11-night trips to the more exotic Southern Caribbean. All cruises sail roundtrip from Manhattan.