Weather difference between September and October

If you Google weather and temperature averages for Istanbul, and the month, then you'll find pages of websites with historical weather averages.

If you look at Rick’s tour to Istanbul, at the bottom it has the average temps and rainfall for each month.

One thing to be aware of is that some of the average temperatures floating around the internet, including those in Wikipedia's city entries, are based on a time period that ends in 2010. I think we are all aware that weather in many places has been wackier recently. and averages are just that--they definitely hide all kinds of day-to-day and hour-to-hour fluctuations.

I believe you'll find very, very few places and times where you can be sure the temperature will remain between 60F and 70F over the course of a month.

For temps in the 60s-70s, October is better. September is usually still quite warm in Istanbul.

Thank you. I was also thinking that October is a better choice.

We were in Istanbul in September and October. We left on 10/12 and it cooled off that very day after a front came in. Up to that time, it was very hot every day.