**Forecast consensus points to a minimum temperature near 20–21°C overnight into September 12, 2026, with models showing only small spreads that keep these two outcomes tightly matched at 50% implied probability each.** Istanbul’s location on the Bosphorus and its urban heat-island effect produce modest nocturnal cooling under clear skies and light-to-moderate northeasterly flow. Multiple numerical weather prediction runs (including GFS-based guidance) indicate the temperature bottoming out between roughly 18–21°C, with the precise hourly minimum sensitive to the exact timing of the pre-dawn low and the reference station’s siting. Recent model updates have not introduced major shifts, and climatological norms for mid-September (roughly 18–20°C) align with the current stable high-pressure regime and absence of significant moisture or frontal activity. Higher outcomes remain near-zero probability because surface observations and ensemble spreads show no support for readings above 22°C, while lower bins (19°C and below) sit slightly behind because the bulk of guidance clusters at or above 20°C. Traders are therefore pricing the narrow scientific uncertainty between the two leading bins rather than any single decisive catalyst.