Persistent cloud cover and showers expected across the Valley of Mexico on September 30 are the main factors capping daytime heating, as low-pressure systems and atmospheric instability maintain high humidity and limit solar insolation. Official Servicio Meteorológico Nacional guidance and multiple forecast models project a maximum of 24–26 °C under mostly overcast skies with 70–85 % precipitation probability, consistent with late-September climatology at Mexico City’s 2,240 m elevation. Recent observations show similar suppressed maxima amid comparable conditions, reinforcing trader consensus around the 25–26 °C outcomes while assigning only modest probability to 27 °C or higher. Updated model runs and any clearing trends ahead of the daily peak will be the key near-term variables.