Persistent cloud cover and frequent thunderstorms during Mexico City's peak rainy season are suppressing the daily maximum below the long-term August average of roughly 23–24 °C. Official short-range guidance points to highs of 18–21 °C under mostly overcast skies with 70–90 % storm probability, limiting solar insolation and triggering evaporative cooling. The market's tight clustering—19 °C at 33.5 %, 20 °C at 26.5 %, and 18 °C at 17.5 %—reflects genuine uncertainty in storm timing, intensity, and local wind patterns that can shift the peak by 1–2 °C. Higher or lower outcomes carry low implied probability because clear breaks or unusual warming are climatologically uncommon at the city's 2,240 m elevation. Real-time surface observations and updated model runs through the afternoon will provide the clearest signals for resolution.