It will most likely be a little cool (high 50's--low 60's) the first couple of days out and the last couple back, but gradually warming as you near the Islands. You might prefer the covered pool on these days; but the rest of the trip will be quite nice.
Also, the first day or two could be a little rough--I say "could be" because it could also be smooth as glass all the way across. If you've never been seasick before I wouldn't worry about it on this cruise. But if it should happen, there are remedies available from the Medical Center and the shops.