**Incoming warm air advection is the dominant driver behind closely matched market-implied odds for São Paulo’s August 28 minimum temperature.** A building high-pressure ridge and northerly flow are replacing cooler air that kept recent overnight lows in the mid-teens Celsius, pushing daytime maxima toward 30–34 °C while limiting nocturnal cooling. Authoritative short-range guidance (GFS, ECMWF, and local Brazilian models) converges on a dawn minimum of roughly 15–19 °C under mostly clear to partly cloudy skies, with light winds reducing mixing and allowing modest radiational cooling. The near-even split between “10 °C or below” (~42.5 %) and “20 °C or higher” (~41 %) reflects residual forecast spread in boundary-layer moisture and exact cloud cover timing; small differences in dew-point depression or residual low-level stratus can shift the overnight low by 2–4 °C. Historical climatology places the typical August 28 minimum near 15 °C, so current model consensus sits slightly above normal yet well short of the 20 °C threshold that would require stronger warm-air advection or persistent cloud cover. Traders are therefore weighting the most recent model runs and any evening satellite trends showing whether the warm surge fully suppresses radiational cooling before sunrise on the 28th.