In reply to Juicefree:
Definitely take a jacket, it may be warm as other people have already said, but it can also be wet in November, often snow in December.
If you have time, I recommend you visit Buyukada, the biggest of the chain of islands called the princess islands just of the Istanbul coast, you can take a ferry for a few lira, I also love visiting the spice bazaar, walkable from Sultan Ahmet