Traders assign the highest implied probabilities to 29–31°C for São Paulo’s August 13 maximum because the latest regional model runs project a peak near 28–29°C under a stable subtropical high-pressure ridge, with modest warming potential from reduced cloud cover and light winds. This setup allows greater solar insolation during the day while limiting convective cooling, though forecast spreads arise from variable timing of any broken cloud layers and slight differences in boundary-layer mixing across ensembles. Historical August climatology centers on 23–25°C highs, so the current warmer signal reflects a transient ridge rather than a seasonal anomaly. Market prices capture this narrow uncertainty range, with resolution hinging on official INMET or airport station readings that integrate precise hourly maxima.