Summer in Greece
Sometimes the holidays in June and September were considered as holidays outside of the season. It's not like that nowaday. Accommodation capacities were fully booked from June 20 to September 10. Both the first half of June and the second half of September are quite demanding, but more and more requests are received for holidays in May and October.
May is the time when the Greek season is already in progress in the south part of the country. Crete and Cyclades are in May like northern Greece in June, so if you want to swim in May, Crete is the right choice for you. October in Crete, and early November, are also great periods for visiting these beautiful islands.
Chalkidiki, Thassos, Thessaloniki and the Olympic regions are "waiking up" in May. Although there are tourists who are swimming in that period, for most, the sea is still cold, about 20 degrees.
However, the days are perfect for sunbathing and resting. The average temperature in May is about 17-18 degrees. The highest temperature is 22 degrees. Mornings are beautiful, and the sea is perfectly clean, crystal clear and colors are never more beautiful than after the winter. If swimming in the warm sea is not a priority on your holiday, holidays in May in Greece may be more pleasant than in the season.
In May first tourists are coming, bars and restaurants are opening and atmosphere is nice. Spring on sea! There is nothing more beautiful than this.
September is also wonderful in northern Greece, especially the first half. It may also be rainy days, but it's mostly sunny. The beaches are empty, there are no noise and crowd, there is a lot of parking place, and the sea is still warm, about 23 degrees. The air temperature is between 23 and 26 degrees. In September there are the most beautiful sunsets.
Beginning of October is usually sunny, but already cold for swimming. The sea is not so cold (20-21 degrees), but the temperature of the air falls to 15 to a maximum of 19 degrees, and often the cold wind starts blowing, from that time until the end of winter. Nevertheless, October is nice for walks along the beach and lying on the beach with a good book.
We must say that Sithonia is two degrees warmer in May and September compared to Thassos, and that Thassos has less rainy days.
Although it is often said that the Ionian Sea is more cold, this is not entirely true, it is even sometimes warmer than the Aegean. However, whether the sea on a particular beach will be warmer or cooler depends on whether. Generally the temperatures of both seas are very similar and with a possible slight difference of degree-two. The Ionian Sea is even by a degree or two warmer in September compared to the Aegean, while the Aegean is by degrees or two warmer in May and June.