From my experience...It will be cool in the evenings INDOORS. The airconditioning is usually cranked up pretty high (I prefer it that way, rather be chilly than hot and stuffy in the dining rooms & theaters). OUTSIDE should be about 70-75 degrees (depending on Mother nature, You just never know), and generally windy as all get out! I love taking a stroll out on the deck at night. It is usually humid though. It will be a shock to go from the AC out to the humidity, but not unpleasant (and vice versa). Actually the smell of the sea at night when you open up the doors to go out is wonderful and something that I look forward to on every cruise!
So, if 70 degrees is chilly for you (I'm from WI, that's a sauna right now!) than you should be prepared with a sweater or sweatshirt or shawl. I generally take one little over the shoulder something or other for the AC in the evenings.
mrsfuzzmo