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The Istanbul Metropolitan Municipality's (IBB) Disaster Coordination Center, known as AKOM, released its weekly weather forecast for Türkiye's largest city, a metropolis of over 15 million people straddling the Bosphorus Strait between Europe and Asia.
According to the report, partly cloudy skies are expected across Istanbul through the week, with showers and locally heavy downpours forecast to begin Wednesday, September 16.
The center's forecast outlines a day-by-day breakdown. Rain is expected Wednesday; intermittent showers are forecast for Thursday, Sept. 17, and a rain warning has been issued for Friday morning, Sept. 18.
AKOM attributed the shift in conditions to intermittent strong winds blowing from the north, combined with overcast skies, and said temperatures are expected to range between 22 and 24 degrees Celsius (72 and 75 degrees Fahrenheit) throughout the week, below seasonal norms for the city.
Istanbul's weather is shaped in part by its position between the Black Sea to the north and the Sea of Marmara to the south, making conditions sensitive to shifts in wind direction.
Rainfall typically increases as the city moves from summer into autumn, with September marking that seasonal transition.
Istanbul has recorded several flooding episodes in 2026.
In July, severe thunderstorms flooded streets and disrupted traffic across both the European and Asian sides of the city, with the districts of Besiktas, Sisli, Kagıthane, Sultangazi, Fatih, and Bakırkoy among the hardest hit on the European side, alongside Umraniye, Cekmekoy, Kadikoy, Beykoz and Uskudar on the Asian side.
A flood-risk study conducted by Istanbul Technical University in collaboration with AKOM found that around 10 percent of the city's surface area falls under high flood hazard, an area that contains a very large population, increasing overall flood risk significantly.
AKOM's report did not include rainfall totals or district-level advisories for this week's forecast.
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