**Forecast models and observational data indicate a highest temperature in Istanbul on September 1 most likely in the 26–28°C range, aligning closely with the market’s leading implied probabilities of 49% for 26°C and 34.5% for 27°C.** Istanbul’s early-September climatology features a transition from peak summer warmth, with average daily maxima near 27–28°C moderated by the surrounding seas (Sea of Marmara and Bosphorus) and prevailing northeasterly flows. Current late-August conditions show highs of 27–29°C under mostly sunny skies and light-to-moderate northerly winds, consistent with the typical Etesian wind regime that limits extreme heat. Short-range models (GFS, ECMWF, and regional Turkish Meteorological Service guidance) converge on 27–30°C daytime maxima for September 1 under continued high pressure, clear skies, and similar wind patterns, with minimal precipitation risk. The concentration of market-implied odds around 26–27°C reflects trader emphasis on the lower end of the forecast envelope, possible measurement at specific urban or airport stations that run slightly cooler than regional maxima, and recognition of inherent model uncertainty in the final 48 hours. Higher outcomes (28°C+) carry low probability due to the seasonal decline from midsummer peaks and the absence of any anomalous warm advection. Updated model runs and official observations over the next day will provide the key data points for resolution.