Hi we are going to Greece September 19- October 19. We are spending 2 weeks on the Pelloponese and then heading to Santorini and Naxos. Does anyone have a 3rd island to recommend? Does anyone know what the weather will be like?
First, the weather will be in the upper 70's during the day and the upper 60's at night. You might consider Mykonos since it would be easy to take the ferry between all three islands, I would start at Santorini then ferry to Naxos then ferry to Mykonos. You can also do the same thing in reverse.
Are you planning on spending any time in Athens?
Are you committed to Peloponnese first?
Where are you coming from? Europe, North America Australia.
Anyway I will make a couple of suggestions.
On day of arrival many experienced travellers suggest you get over jet lag on an island. You need about 2 hours to make a connection to an Aegean or Sky express flight. So I would suggest you fly immediately to Santorini on day of arrival.
I make this suggestion based on daily temperatures. It will be warmer in Mid September than it will be in early October. Do your islands first to improve your chances of nicer warmer weather. The Peloponnese trip is not quite as important to have warmer weather.
My wallet can only stand 3 nights in Santorini but it really is spectacular. How long will you have on Santorini. (Lets say 3 nights.)
4 nights is probably better.
Santorini https://www.flickr.com/photos/stanbr54/albums/72157632154800782
Naxos is our favourite Island in the Cyclades. Naxos needs a week at a minimum 10 days will allow you to explore the island pretty well. But lets say a week for Naxos (thats 10 days.)
Around Naxos town 2022 https://www.flickr.com/photos/stanbr54/albums/72177720299959098
Back to Naxos 2022 https://www.flickr.com/photos/stanbr54/albums/72177720299940917
Chalki to Vivlos villages https://www.flickr.com/photos/stanbr54/albums/72177720299950915
Day trip to Delos and Mykonos https://www.flickr.com/photos/stanbr54/albums/72157637922138466
That leaves you 4 days to visit another island and or Athens.
Keep in mind you need to be in Athens the night before your return trip.
Frankly you might want to spend those 10 days in Naxos and do a day trip excursion to Delos and Mykonos perhaps the small Cyclades and save at least one night in Athens at the end of your trip.