Recent model runs indicate a cold front and associated thunderstorm activity arriving in São Paulo around September 1, sharply lowering daytime maxima after unusually warm conditions on August 30–31. Official guidance from sources such as the Met Office and multiple ensemble forecasts places the most likely high near 22–23 °C under widespread cloud cover, moderate northwest winds, and 5–17 mm of rain, limiting solar heating. Spread among deterministic models arises mainly from differences in frontal timing and boundary-layer moisture, with some solutions allowing brief clearing that could push readings to 24–25 °C while others keep persistent rain and keep temperatures closer to 21 °C. Historical September averages near 23 °C provide context, yet the imminent synoptic shift dominates trader assessments reflected in the tightly clustered market-implied probabilities.