While the resort city of Antalya is located in the hotter southern regions of Turkey, temperatures still mellow during September to a daytime average of 30°C. Rain is rare in Antalya during September, and seawater temperatures sit at a pleasant 20°C, ideal for taking a dip. You'll be pleased to know that beach clubs in Antalya stay open until mid-October, too!
Marmaris is a Mediterranean resort town situated on the Turkish Turquoise Coast, and September is a great time to visit. Temperatures are still extremely warm, sitting at a toasty average of 25°C, and rain is very rare. It's easier to relax without the crowds of visitors during July and August, and the sun still shines for an impressive 11 hours a day, so you can spend plenty of time on the beach.
The ancient Turkish city of Ephesus is brimming with culture, restaurants, and opportunities to relax under the pleasant September sun. Daytime temperatures still usually reach the mid-20s, and sea temperatures average at a pleasant 22°C. Ephesus is home to one of the Seven Wonders of the Ancient World: the magnificent Temple of Artemis.