Istanbul has a subtropical and Mediterranean climate. The temperatures of Istanbul average at 82F, with July and August being the warmest months. In the winter temperatures fall to the 50s or low 60s. To get a 10-day forecast and view satellite images for Istanbul, visit The Weather Channel or Yahoo! Weather.
Istanbul is breath-taking from April to October. The weather is gorgeous, water is great and there are plenty of summer sports to enjoy. However, I do not think that this it is such a bad idea to travel off-season, save on the cheap hotel rates and avoid huge tourist crowds. You may need a sweater but it is still much nicer than most European capitals, the American East Coast or Midwestern cities. Still sunny and the view of the Bosphorus is always there to enjoy!
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