Forecast models from sources including Open-Meteo, the Met Office, and GFS runs show Istanbul’s October 15 high likely peaking near 15°C amid persistent showers, full cloud cover, and northerly winds of 20–40 km/h that advect cooler maritime air. These conditions suppress daytime warming, consistent with climatological October norms around 18–20°C but lowered by the active frontal system delivering 20+ mm of rain. Market-implied odds heavily favor 15°C because ensemble guidance clusters there, with only modest upside risk if breaks in cloud allow brief warming to 16–17°C before evening. Updated model runs and real-time observations from local stations will refine the exact maximum before market resolution.