Istanbul Weather

You can experience all four sessions in Istanbul.
Spring is April-May-June where it is best to visit if you don't like very hot weather . You can go for swimming as of early June or travel without sweating after mid May. April may be a little more rainy then rest of the months. I would prefer end of May till 15th July for perfect weather if you don't like hot weather.
Summer is Spring is July-August -September where 't can be hot but as hot as Dubai. As it is the top session, hotels may get full and more expensive. At the same time Istanbul will have less traffic as locals take annual leaves and move to east and north parts of Turkey for vacation.
Autumn is October -November -December where wheather will stil be prettly warm and you can walk and will not require cold gear . October and November is good and sun fall will be around 7-7:30 pm. As local , we really enjoy this months after a hot summer as it is
Winter is January- February-March where there will be some days with snow and lots of rainy days. As Turkey is close to equator, even in winter we can have 15 Degreees/ 59 Fahreneit days . Best will be to have a water resistant jacket and umbrealla . Some days can be even cooler but usually daytime it is rarely under 0 degrees/ 34 Fahrenheit. Accomodation is cheaper as it is off session but if you want to get a hair transplant or cosmedic operation prefer this months as you should avoid sunlight and cold air is better.