Weather in Greece mid/late May VS or late Sept /early October

I usually visit Greece in mid/late September. It does depend on how far into the month you go (and where specifically in Greece). We normally go last week of summer and when I look at the forecast I can see the weather is starting to turn right after we leave. Some locations can also be extremely windy (we found this in Hydra). I personally wouldn't go much later than that, and I know a lot of the seasonal restaurants etc start closing up at the start of October. However, mid September is definitely warm enough to go to the beach. It's also a nice time to go as in most countries the school term has just restarted so it's less busy. I've not gone in May but my sense is the water will still be quite chilly (I'm sure others here can share personal experiences). Kalo taxithi.

Thanks and yes we're inclined to take the Sept 25-Oct 8th RS tour. If you were going to visit an island pre-tour. Which would you choose? for 3-4 nights?

Hi again. Our Greece tour started Sept.23 (2024). We had wonderful weather, and 3 opportunities to swim in the beautiful Aegean or Mediterranean! First in Kardamili. (a must eat restaurant is Lela's Taverna, make a reservation, ask for table closest to water's edge - so beautiful, they might call it "Rick's Table"!). Second was Monemvasia. I didn't swim there. some tour members did and loved it.
Third was Hydra (my favorite for swimming) Where you will have a free day, We took a little foot ferry ($20 RT) to Vlychos Plakes Beach. It was perfection. We stayed for hours. Umbrellas with lounge chairs. Some tour members walked (3 km) from the main port area. Along this walk you can see the Leonard Cohen memorial bench - beautiful spot to sit and gaze at the amazing blue sea. Enjoyed this tour so much; loved the Greek food, the people, the guides - especially Mama Faye in Athens.

We always go to Greece in May/mid-June or September. The sea temperature is a bit chilly in May, and there have been years when we hardly swam at all. June is much better.

For swimming or any other water activity, September is ideal.

On the other hand, if you're looking for lush greenery, you'll find it in May when the landscapes are still green and the vegetation in bloom. By September, that's all over, the vegetation left on the islands is yellow and scorched, except for some higher-altitude areas.

If you were going to visit an island pre-tour. Which would you choose?
for 3-4 nights?

I guess that without further information about your preferences, the suggestion of Naxos should be unanimously approved by the RS members.

For me, a 2-week visit from about May 20 to early June is just perfect ... everything's open, nothing is crowded, he days are looong, the temp is between 70 (early am) mid 80s (afternoon). The greenery is lovely, flowers are out... and the arly veg & fruit crops are in the markets. I'm an avid swimmer, need to have at least a dip dailly in Naxos, and several long afternoons ... and for me the water tempis just fine... a bit brisk for the first 20 seconds, then sublime. I do swim in CT, but am not a penquin.

I've not been to Naxos so can't comment (tho it sounds very nice)- of places I've been, I might suggest Skopelos, which was beautiful and warm and not crowded in mid September. You can get there either by flying to next door Skiathos, ferry from Thessaloniki (but these finish sometime in September so check your dates), or ferry from Volos.

I've only been to Greece in June once, which was Corfu combined with a trip to southern Albania. One day the weather was so bad they actually cancelled the Corfu/Sarande ferry for the day, but the rest of the time it was beautiful and warm enough to go in the water. Honestly tho you can't really go wrong in Greece, and I am sure you will enjoy whatever you choose!