June - September are generally the rainy months. Having said that all Caribbean rain tends to be short sharp showers. We went on the Arcadia in Jan and found it to be very wet each day, but only for a short time, still plenty of hot sunshine to come home a nice colour.
Don't panic you will have a great time, despite the comments people have made about the Arcadia, you will have a great time.
We have been to the Caribbean 3 times in either January or February. Both times we've been to St. Lucia there has been a short spell of rain but it soon clears. When we were in Martinique and Dominica on our first cruise it was drizzling for part of the day but that was about all. I did carry a very small umbrella and found that some other women did too. Mind you it seemed very odd walking through the rain forest in St. Lucia with a M&S umbrella up! You'll have a fantastic time, don't worry about the weather.
Although October to March are the best times for less rain, yes you will need a brolly. Don't worry showers are heavy and brief plus it's still hot. it won't affect your enjoyment of your holiday. I've been to most of the Caribbean and all different times of the year and loved it, especially St Luci.
Just returned from New Orleans on Arcadia. Started at Barbados.Holiday wonderful, rained in St Lucia and Domi
nique, apart from that 12 days of Sunshine. Cozumel was great. well done P & O.