We have been on the Star the last 2 years during October half term. In 2006 the weather was beautiful - nice and hot most days. Last year however, it was alot cooler, rather windy in the afternoons and not very sunny apart from one day in Nice! It wasn't cold but you really needed a long sleeved top in the late afternoon and it wasn't sitting-out-on-deck weather after about 3.30pm. Hope this year is better as we are also going again on the 25th!!
We were on the Island Star last year at the same time, (English school holidays). Certainly a bit colder than we anticipated. Layer dressing is the answer. Chilly late afternoon on deck, cardigans or wraps would be a good idea. On our excursion to Florence we were frozen - the locals were wearing coats and jackets. We ended up purchasing scarves and wraps in Florence.