**Forecast models from multiple sources, including INMET-aligned data and global ensembles, currently point to a minimum temperature near 19–22°C in São Paulo on September 30, driven by moderate nocturnal radiative cooling under variable cloud cover and light northerly to northwesterly winds.** Daytime highs are expected around 30–36°C amid spring warming, with possible afternoon showers or thunderstorms that could limit evening temperature drops by increasing humidity and reducing clear-sky heat loss. Historical September minima average near 12–14°C, but recent conditions reflect a shift from an early-month polar air outbreak that produced record-low daytime readings; the current pattern favors milder overnight lows closer to seasonal norms. Trader sentiment remains evenly split between sub-15°C and 25°C+ outcomes because ensemble spreads and local microclimate effects (urban heat island versus station siting at Mirante de Santana) introduce meaningful uncertainty within the narrow 48-hour window. New model runs and official INMET observations over the next 24–48 hours will be the key catalysts, as resolution hinges on the single lowest verified reading for the calendar day.