Hi Rose.
Having travelled there over quite a number of years I think that I know Croatia fairly well by now. Wonderful country and people. Sadly this is one trip I can't do, because of slight mobility issues, although I would love to.
I've been mainly in May and September and have encountered many types of weather, although it has never been cold. I was in the Dubrovnik area this year at the beginning of May, and the weather was a bit changeable, but when it finally cleared up it was stunning. Clear blue skies. I never found it baking hot to be honest, but it was certainly warm enough for t shirts even at night. The humidity bothered me a bit, but you wouldn't have that problem at sea.
I hope you decide to go. :)
Glad to hear the trip is going well Sally. Can't wait to read your review! 😃