For the most part, it should be warm, temps don't vary all that much in the Caribbean during the year. I'd pack at least one pair of jeans/pants and a sweater, you could get the cooler day or two.
for daytime wear you will be living in shorts & t-shirts, tanks tops etc.
I pack a lightweight track suit for cooler/breezy days/nights just in case.
I also pack a lightweight sweater to throw over my shoulders at night as the dining room and show lounges can be chilly.
If your formal wear is sleeveless or less, it is also a good idea to pack a wrap, stole, or pashima
Hubby wears or packs a lightweight London Fog type jacket.
The only times I've been to W. Caribbean was in Feb
Average temps were 75-80 degrees. Had 1 very short, fast moving, sping shower in Belize one year, it lasted all of 10 minutes, and it was warm.
We prefer going in Feb because the 'rainy season' is pretty much past and it's not real hot and humid yet. We'll be there the week of 2/10-2/17 on NCL this year.
Hope you have a great time!