However May is ALMOST ALWAYS very cold. You will need hats and gloves and thick parkas.
On our Sept 05 cruise, it rained 6 days out of the first 7 - South Bound. The pool deck was so wet that no matter how hard the crew tried to vacuum the water, the turf still soaked and was yuckky to walk on.
They do provide blankets for people want to stay on the pool deck ...
There is a covered pool on our Island Princess and the hot tubs are working. So if you so insist, you can use those.