The weather will certainly be becoming warmer by then indeed it can be hot. So in the 70s most of the days although the nights can be chillier but it would be unusual if they were very cold. You must, at that time of year, be prepared for rain at times and even the odd storm but unless you are very unlucky the weather should be very enjoyable. Don't forget though that the sea will not have warmed up too much by that time and it will be even colder where large rivers flow into it like the Adriatic which takes a great deal of water from the Alps etc........Nei.
Thankyou very much for your informative answer it will definitely help us with choice of clothes.
We are doing the same cruise, and last year did the same time cruise around Spain, Portugal. Very very pleasant weather. Would anticipate similar to UK late June weather, and apart from obvious light shower wear or umbrella, we will be taking normal Summer clothes. Cabin C 307 Caribe, will look out for you!