Weather in Istanbul in December

A hard month. December is a hard month in Istanbul, and worth planning around. Highs sit at 10.4 °C and the day is short; this is an indoors-with-excursions month, not an outdoors-all-day one.

December ranks 10 of 12 — near the bottom of Istanbul's year. May is the month that works, and the swing between the two is 48 points, which is a different holiday rather than a slightly better one.

Rain on 12 days, 2 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at 10.4 °C the difference between a good day and a miserable one is entirely down to what you are wearing.

What the averages hide

Averages flatten a month, and this one hides a few things: the day barely swings — 4.6 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest December day reached 20.3 °C and the coldest night fell to -3.1 °C, and the wettest single day dropped 35 mm — roughly 43% of the month's rain in one day.

December is moderately variable: 19 mm in the driest year against 201 mm in the wettest, around an average of 82 mm. Roughly two Decembers in three land near that average, and the third does something else entirely.

Wind is light at 15.1 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 82%, which at 10.4 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How December sits in the year

The month is on the way down: 4.8 °C cooler than November, with January dropping another 2 °C. The first week and the last are not the same trip.

Daylight in December

December sits at the dark end of Istanbul's year — 9.3 hours of daylight against 15.1 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

Sea temperature

The sea sits at about 11.3 °C in December — too cold to swim without a wetsuit. The sea peaks at 25.6 °C in August and bottoms out at 7.5 °C — water lags the air by a month or two, which is why the best swimming often comes after the best weather.

How busy it gets

Quiet. Few other visitors, cheaper rooms, and a real chance some seasonal operators are shut.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

December in Istanbul versus nearby

If Istanbul is one option among several, the nearby comparison is worth making. Bursa is close enough to be a coin toss — within a degree on temperature, the same number of rain days. Eskişehir is the weaker option in December — 2.7 °C cooler, 1 day less rain.

So: December is a compromise. May is 40 points better and is what Istanbul is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Istanbul

See all twelve months in Istanbul, or where else to go in December.