Traders see closely matched probabilities for a 16–17°C low in Istanbul on September 17 because current model guidance and real-time observations cluster in that narrow range amid typical early-autumn conditions. Northeast winds, increasing cloud cover, and light or patchy precipitation limit overnight radiative cooling over the urban and coastal zones, while the moderating influence of the Sea of Marmara prevents deeper drops. Forecasts from multiple sources consistently project a nighttime minimum near 16–19°C, aligning with the September climatological average of roughly 17°C. The tight spread among the leading outcomes reflects residual uncertainty in exact minimum readings, which can shift with final model runs, local microclimate variations, or precise measurement timing at official stations. No major synoptic changes have altered the outlook in recent days.