Recent forecasts from multiple models, including Yr.no and Met Office guidance, indicate a minimum temperature near 13–14°C for São Paulo on September 16, driven by a lingering polar air mass and associated cold front that has suppressed daytime heating and limited nocturnal radiative cooling under mostly cloudy skies. Southeast winds of 3–5 m/s, rising surface pressure near 1020–1024 hPa, and light precipitation potential further moderate overnight lows by enhancing mixing and reducing clear-sky heat loss. This positions the outcome near the middle of the distribution, where small shifts in cloud cover, wind speed, or model bias could differentiate between sub-12°C or mid-teens readings. Trader balance around the 9°C-or-below and 19°C-or-higher brackets reflects uncertainty in short-range model consensus ahead of updated runs, while historical September climatology (typical lows near 14–16°C) provides context for the current cooler anomaly.