Persistent atmospheric instability across southeastern Brazil, driven by a low-pressure system and high moisture content, is producing widespread cloud cover, scattered thunderstorms, and moderate to heavy rainfall on October 15, which limits daytime heating and caps maximum temperatures. Official guidance from INMET and ensemble models such as GFS indicate a likely peak near 24–26 °C amid frequent convection, yet the market distribution—led by 27 °C at 33 % implied probability—reflects trader assessment of residual uncertainty in storm timing, localized clearing, or weaker-than-expected precipitation that could allow brief warming to 27–28 °C. Historical October maxima average 24.9 °C, while current humidity above 70 % and winds of 7–10 mph further moderate extremes; updated model runs and surface observations tomorrow morning will be the key resolution inputs.