Giresun has a borderline oceanic/humid subtropical climate; like most of the eastern Black Sea coast of Turkey; with warm and humid summers and cool and damp winters. Giresun has a high and evenly distributed precipitation throughout the year. Precipitation is heaviest in autumn and spring.
Snowfall is quite common between the months of December and March, snowing for a week or two, and it can be heavy once it snows.
The water temperature, like in the rest of the Black Sea coast of Turkey, is always cool and fluctuates between 8° and 20°C throughout the year.