Recent forecasts from multiple models indicate a high near 23–25°C for São Paulo on September 18 under partly cloudy skies with persistent easterly winds of 7–11 mph and limited moisture. The market’s tight clustering around 22–24°C reflects genuine uncertainty in peak daytime heating, driven by variable cloud cover that could suppress or enhance solar radiation and small differences in model timing of maximum temperatures. September 2026 has run notably cooler than historical averages, keeping baseline conditions modest and limiting upside to 25°C or higher. Official resolution will hinge on the precise maximum recorded at the designated monitoring station, where even modest shifts in afternoon cloud thickness or wind speed can swing the outcome between the leading bins.