Istanbul, where it is

The climate of Istanbul, the largest city of Turkey, can be defined as transitional Mediterranean, in fact it has fairly cold winters, but otherwise it has Mediterranean characteristics: the rainiest seasons are autumn and winter, and summer is hot and sunny.
Here are the average temperatures.
Istanbul - Average temperatures
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)435813182020171386
Max (°C)9912172226292925201511
Min (°F)393741465564686863554643
Max (°F)484854637279848477685952

Precipitation amounts to about 820 millimetres (33 inches) per year; the wettest months are December, January and February.
Here is the average precipitation.
Istanbul - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)110907045403535306080105120820
Prec.(in)4.33.52.81.81.61.41.41.22.43.14.14.732.3
Days1211106543258111390

Winter, from December to March, is quite cold: the average temperature in January and February is 6.5 °C (43.5 °F). In winter, there are mild periods, but also cold periods, when the temperature remains a few degrees above freezing (0 °C or 32 °F) even during the day, and a cold rain can fall, or even snow. In fact, snowfalls are not so rare, and occur more than once almost every year, accompanied by frosts, usually not intense. This chance of cold weather and snow is due to the proximity to the Balkan Peninsula, which in winter cools down a lot. March is usually quite cold, and is often still a wintery month. The most abundant snowfall occurred on 3 March 1987, with 63 cm (24.8 in). In February 2015, the snow reached 75 cm (29.5 in) in the nearby town of Çatalca, belonging to the metropolitan municipality of Istanbul.

Spring, in April and May, is mild, and sunny days become quickly more frequent, while the rains become rarer. However, in April it can still be cold, and there may be sudden changes in temperature, especially in the first half of the month.

Summer, from June to August, is hot and sunny, and also quite sultry; the heat is felt especially within the city, while a relieving breeze blows from the sea. The average temperature in August, which is albeit slightly the warmest month, is 24.5 °C (76.5 °F). However, during the warmest months, July and August, and more rarely in June, sometimes the temperature can reach 35/37 °C (95/99 °F). The sky is mostly clear, although we can not exclude some downpours or thunderstorms, generally not intense.

Autumn, from September to November, is initially warm and often sunny in September, but weather fronts of Atlantic origin gradually become more frequent, so that there are on average 5 days with rainfall in September, 8 in October and 11 in November.

Istanbul

The amount of sunshine in Istanbul is scarce in winter, when cloudy skies prevail, and sometimes fog can form, while it is very good in summer, when sunshine prevails.
Istanbul - Sunshine
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Hours234681010108532

The sea in Istanbul, very cold in winter, becomes warm enough for swimming in July and August, while it is still very cool in June, about 20 °C (68 °F), and all in all it's still acceptable in September, when it's about 22 °C (72 °F), as can be seen in the following table.
Istanbul - Sea temperature
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Temp (°C)988101520232422191411
Temp (°F)484646505968737572665752

When to go


The best times to visit Istanbul are spring and autumn, in particular the months of May, June and September. September is an interesting month, especially in the first half, usually pleasant and with little rain, and the sea is still warm enough. In July and August, at certain times the heat is acceptable, while at others it can be intense.