**A cold front advancing across São Paulo state has driven cooler, moist maritime air into the region, producing the leading market-implied probability for a minimum of 11 °C or below on October 3.** Official short-range guidance from Brazilian meteorological sources and international models (including Met Office and Yr) currently converge on overnight lows near 15 °C under mostly cloudy skies with light drizzle or garoa, following maximums of 22–24 °C. This represents a several-degree drop from seasonal early-October normals of roughly 14–17 °C, driven by the frontal passage and easterly flow off the Atlantic that limits radiational cooling. Model spread remains modest but includes downside risk if thicker cloud cover or a slightly stronger surge of polar-modified air arrives; updated runs and official INMET briefings on October 2 will refine the exact minimum and directly influence resolution probabilities.