Weather in January can be good or bad. We sailed the Eastern last Jan 19 and the weather was beautiful- highs in the mid 80's. The cruise before us had a cold day at Castaway Cay though. The water for our cruise was a little chilly to me but was OK after a while. The water in St Maarten was nice and I didn't get into the water in St Thomas.
If a cold front dips down into lower Florida it could affect the weather a Castway Cay.
Except for Castaway Cay you should have nice weather. I would sail again in January. The week before we sailed last year was when we got over a foot of snow here. So it was kind of strange going to the port to board the ship in shorts.
my understanding is that the Eastern and Western both entertain basically the same weather. Expect 80's. We did the Eastern last December and it was beautiful!
i have done both routes in January. The weather was good both times on each route, so I don't think that there is going to be a lot of differences in the weather based on the itinerary that you select...
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