Recent forecast models from sources including GEM, ECMWF, and local monitoring point to a daytime high of 25–26°C in Mexico City on September 28, driven by the city’s 2,240 m elevation, typical late-September cloud cover, and scattered afternoon showers that cap solar heating. These conditions align with climatological baselines near 23–24°C and explain why traders assign the highest implied probability (44.5%) to exactly 26°C, followed by 27°C or warmer (30.5%). Persistent moisture and variable steering winds introduce modest upside risk if clearing occurs earlier, while heavier rain would favor the 25°C bin (22.5%). Updated model runs and official Servicio Meteorológico Nacional guidance on precipitation timing remain the key near-term catalysts.