Mostly ! As with anywhere nowadays you cannot be 100% sure. In June this year it was horrible and wet til mid June apparently. We arrived 15 June and it got hotter by the day, and we only ever got rain in the evening.
Anyway, when we lived there for three years May was usually very nice. The first year it was very hot, the second year we arrived 1 May and it was quite cold - 17 deg C. The third year back to what we would call normal at 1 May was about 20 deg.
I am sure you will get some good weather. May is reknowned for being a bit iffy though in Greece and the islands. But any rain in usually shortlived. I would take a brolly and a jacket/cardigan for evenings as they are still quite cool in May.
Hope this helps.
Jane
