Trader consensus strongly favors 21°C as São Paulo’s highest temperature on October 5, driven by convergent forecasts from multiple meteorological models showing a daytime maximum near that threshold under persistent overcast skies and light showers. Official guidance highlights southeasterly flow, high humidity above 70 percent, and limited solar heating that caps afternoon readings around 21–22 °C, consistent with early-October climatology for the region. Near-term model runs and observational trends support this narrow outcome window. A realistic challenge would require either rapid clearing that allows greater insolation or an unexpected warm advection event pushing verified station readings to 22 °C or above before midnight local time.