The local climate, more temperate near the Gulf of İzmit (Körfez in Turkish) and the Black Sea, more severe in the mountains, constitutes a transition between Mediterranean and Black Sea types; the typical urban summer here is hot and dry, the winter wet, however, Izmit and Marmara lack the refreshing summer breezes of the northern reaches, and can become humid.
The highest recorded temperature in the city (11 Aug 1970) was 41.6°C , the lowest (4 Feb 1960) -8.7°C , while the yearly average stands at 14.8°C .
The Black Sea coast sees an annual rainfall of 1000mm., which gradually lessens south-eastwards: Izmit, for example, generally gets less than 800mm. The south-facing slopes of the Samanlı mountains, near Körfez, experience conditions similar to Black Sea coastal regions. Winter winds blow from the south to south-east, while in summer mainly south-easterly.