Rhodes is one of the most southern islands
in Greece and has a milder climate than the Cyclades and the
islands and mainland to the north. Therefore Rhodes has always
had the longest season of any of the islands, lasting from the
beginning of April until the end of November. But you could
visit Rhodes from December until the end of March and have a
good time too. The city is large enough so that it does not
close down in the winter. There are shops, restaurants, cafes
and hotels open all year and though there will be a majority
of days when it will be too cold to swim there will still be
plenty to see and the experience of exploring the old city without
all the tourists around is something I look forword to.
If I were coming to Greece in the winter season and had to choose one island to visit then this would be the one, though I would probably fly rather then take the ferry, to avoid storms and sea-sickness. As for other times of year we were there at the hottest time of the summer and it was fine. Even the hottest part of the day you could find somewhere to stay cool, either by the sea, in the shade in one of the many parks or in a cafe. Even the hottest days the mornings and nights were fine. When the summer meltemi winds are blowing the climate is perfect. I can't imagine it being any better in April, May, June, September and October but they say it is.
Keep in mind that there are fewer island connections in the winter and getting from Rhodes to Santorini and the other Cyclades, which is hard to do even in the summer is much more difficult in the winter. There is a ferry to Crete which continues on to Milos and Santorini a couple times a week but this is a long trip, especially in the winter when the open sea can be rough. If you want to see what is possible try www.greecetravel.com/create-an-itinerary
You can get discounted rates at hotels in the off-season through Fantasy Travel at www.fantasytravelofgreece.com
