**Forecast models and official guidance point to a high of 24–26°C in Mexico City on September 30, 2026, with trader probabilities clustered around 25°C and 26°C.** Late-September conditions in the high-altitude Valley of Mexico feature the rainy season’s typical cloud cover, afternoon convection, and moisture from southerly flow, which limits daytime heating. Multiple sources, including the Servicio Meteorológico Nacional and numerical models, project maxima of 24–26°C amid overcast skies and periods of rain or thunderstorms, consistent with seasonal norms near 25°C. Recent developments show continued moist, cloudy conditions rather than clearing that could push readings higher. Hourly guidance indicates temperatures climbing through the morning to peak near midday or early afternoon before showers and increased cloudiness cap further rises. This setup favors the 25–26°C range while keeping 27°C+ less likely unless models shift toward reduced precipitation and stronger insolation. Resolution will depend on the official daily maximum reported by Mexico City’s meteorological network, with the current consensus reflecting the balance of expected rain-cooled air and typical late-summer warmth.