The temperatures should be the same regardless. The area is in the Tropic of Cancer and the suns rays are almost overhead anyways in that area. The same holds true of the Equator and the Tropic of Capricorn. After one gets to the outer extremes of the Tropics, the weather starts to cool off depending on the season in that part of the globe.
Leaving the US will be cooler in January and warmer in March.
Class is dismissed.
Good people sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf.
Courage and perserverance have a magical talisman; before which difficulties disappear and obstacles vanish into the air.
Pick your company wisely! Hang around people who are going to help you become all God created you to be.
Here's links to monthly average temps for two popular W. Caribbean ports. They show March slightly warmer, and as the previous poster mentioned, leaving the states will also be slightly warmer. We cruise that time of year due to price and it breaks up the long NE winters. Might be a little cool first nite on deck, but it's gorgeous the rest of the trip.
Go for the best price/cabin/itinerary arrangement. There is little or no difference in weather once in the tropics.
RCCL Independence 4/4/09 - Revenge of the JUGS
Carnival Liberty 3/25/07 - "Spring Break" J.U.G.s (Just Us Girls) Cruise - plus my kids
Carnival Liberty 11/20/05 "I ain't cookin' Thanksgiving dinner" Cruise
NCL Norway - "I'm Pregnant with a 1-year-old" Cruise
Carnival Destiny 6/28/98 - "Honeymoon from Hell" Cruise
Royal Caribbean - 1988 - "Ex-Husband" Cruise