Four seasons can be lived in İstanbul as the same as every region of Turkey. The best time to visit to Istanbul is in spring ( April-May). In this season it is so rainy but also marvellous. If you take a raincoat , you can feel the revival of the nature which is unique in Istanbul especially in Bosphorus. You must see the Judas-trees in spring in Bosphorus. These trees have been grown in Bosphorus since Byzantium. And also the color of the tree had been used as the legal color of Royal. Nowadays, this color is used for the buses of İstanbul and it makes İstanbul a dream city.
It is hot and steamy In summers, especially it is hard to move in Istanbul in August. However, you can go to swim around Istanbul . There is a few beach in Istanbul can be swim like Prince Islands. If you have time you can leave İstanbul and you can go to the Black Sea seaside, Kilyos,Sile, Agva etc. There are many beaches …
You can take a fresh breathe in Autumn because in this season it is less steamy and much fresh. If you have a plan to visit to İstanbul in Autumn, you should take a raincoat and sweatshirt and an umbrella.
If you prefer travelling in winters, you should know it is so rainy and sometimes it is snowy in Istanbul and you must bring a coat and an umbrella.
Today weather in Istanbul
Average Weather for Istanbul (2010)