Forecast models and official guidance point to a daytime maximum of 25–26 °C in São Paulo on August 21 under increasing cloud cover and late showers, following a warmer prior day. This modest cooling stems from the arrival of a cooler air mass behind a frontal boundary, typical for late austral winter when climatological August highs average near 23–24 °C. Model consensus on the precise peak remains tight, with small differences in timing of the front and boundary-layer mixing creating the narrow spread between the leading 25 °C and 26 °C outcomes. Traders weigh these variables against historical variability in frontal passages, where even modest shifts in cloud timing or wind direction can alter the recorded maximum by 1 °C. Updated model runs and real-time observations will refine the final reading before market resolution.