Recent rainfall forecasts tied to typhoon remnants have become the main driver behind Polymarket odds clustering around 29–31°C for Beijing’s August 13 high. Official guidance and ensemble models indicate increased cloud cover, moderate to heavy precipitation, and reduced solar insolation through the day, which limits surface heating and caps maximum temperatures relative to drier climatological baselines near 31–32°C. Moisture from the East Asian monsoon further enhances evaporative cooling and suppresses diurnal warming. Model spread remains modest but centers on 26–30°C outcomes, with traders weighting the balance between lingering instability that could allow brief clearing and sustained overcast conditions that favor the lower end of the range. Updated numerical weather prediction runs tomorrow morning will likely refine these probabilities ahead of market resolution.