Weather in Istanbul in September

How September compares

September is the 4th warmest month of the year in Istanbul and ranks 109th of 134 destinations we compare for September - see where else is hot in September. Within Turkey it is 16th of 18 (Turkey in September). Against London's average high of 18.6°C in September, Istanbul is 5.5°C warmer by day and 7.3°C warmer at night.

Daytime and night-time in September

The typical September day in Istanbul peaks at 24.1°C, but that is an average: the warmest 10% of days reach 27.8°C or more. Roughly 1 in 2 days top 25°C and 1 in 63 pass 30°C. Nights average 18.5°C; one night in ten drops to 15.3°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest September day here reached 34.6°C (2017-09-20) and the coldest night 11.7°C (2019-09-23).

Rain in September

Some rain (4-8 rainy days): about 6 days with 1 mm or more, 45 mm in total. Year to year it varies a lot - the wettest September was 2008 with 115 mm, the driest 1994 with 1 mm. Humidity averages 70%.

Sea temperature in September

The sea averages 22.5°C - warm enough to swim (22°c+). Depending on the year it ranges from 21.4°C to 23.6°C. For the warmest sea here, come in August (24.4°C).

Sunshine and daylight

Around 8.2 hours of sunshine a day (estimated from cloud cover), 12.3 hours of daylight: the sun rises about 06:45 and sets about 19:14 local time in mid-September. Average cloud cover is 33%.

Is September a good time to visit Istanbul?

Yes - it is one of the better months: warm days, manageable rain and long sunny days. The best months for Istanbul on our scoring are August, July, June; months averaging 25°C or more: Jul, Aug.

Warm enough for light clothes, rarely very hot

Istanbul’s average September high is 5.5°C above London’s, so the change should feel noticeable without usually being overpowering. Days reach 25°C about 42% of the time, while 30°C is much less common, at 2%. That makes September a sensible choice if you enjoy warmth but find hotter weather tiring when walking around a city. Light, breathable clothes are a useful starting point, with a shaded break at midday on warmer days. Evenings are generally mild, though the cooler nights can fall to 15.3°C or below, so bring a jumper or light jacket rather than relying on summer clothes alone.

Plenty of outdoor time, with a rain backup

September brings about 8.2 hours of sunshine within 12.3 hours of daylight, leaving plenty of scope to spend time outside. The catch is that rain remains part of the picture: about 6 days receive measurable rain during the month. A compact umbrella or light waterproof is worth packing, and it helps to keep indoor plans flexible rather than committing every day to being outdoors. The monthly figures do not tell you how long any shower will last, so do not assume a rainy day is a write-off. Equally, sunshine is not guaranteed throughout your stay; check the forecast before choosing your longer walks.

Swimming is reasonable, but keep expectations flexible

The sea averages 22.5°C in September, warm enough for swimming, though it may feel fresh as you get in. The year-to-year range is 21°C to 24°C, so your experience could sit anywhere from bracing to more comfortable. If swimming matters to you, September is a reasonable option, but it is better treated as part of a city holiday than the sole reason to travel. Humidity averages 70%, which can make warmer spells feel sticky; loose clothing is useful. Pack swimwear alongside your walking clothes, and favour a warm, settled day for a dip rather than assuming the sea will feel equally inviting throughout your visit.