Hubby and I did this cruise last year. Weather was very mixed. Poured with rain in Dubrovnik. Cool but dry in Rome and Venice. Very warm the day we left Palma and again when we got back. Nice enough for sightseeeing but not sunbathing weather. The last day and night at sea was very rough. The show at night was to be the Talent contest but firstly that was cancelled as insurance for non staff on stage was a problem in rough seas. Then the whole show was cancelled as it was considered too dangerous for the dancers etc. Lots of people didn't make it to dinner that night including us, but we did go to the buffet later. Ship was very quiet as most people stayed in their cabins and got an early night. Next day it was like a millpond. It was a very enjoyable cruise and we almost booked again for this year but wanted to check reviews of the Escape first.
You should note that this cruise is on Island Escape, not Star, and Escape is not the best of ships in a rough sea. At that time of the year you take a chance with the weather and it can be rough (and cold). In the winter you can get the Bora wind in the north Adriatic which brings strong cold winds from the north.
Thanks Bradley and Sutton. Your comments have given my parents something to think about.