If you are concerned about the weather do be aware that that temperatures in the Borum area of Turkey are regularly in the 35-40C range in August. The best time to go to Turkey (or Greece) is either May/June or later in September / early October.
Koh Samui is actually in dry season in August - if it does rain it should be a short burst - even Phuket which is in the rainy season normally only has an hour or so a day.