**Heavy rainfall and associated cloud cover on September 3 are the main drivers positioning lower temperatures—particularly 22°C or below—as the leading market outcome at 43.5% implied probability.** Persistent easterly flow and a strong precipitation signal (90%+ chance, with totals of 20–110 mm across models) will suppress daytime heating and enhance overnight radiative cooling in Taipei’s subtropical climate, where early-September climatological lows average near 23–25°C. Multiple forecasts, including international models, show overnight minima around 24–25°C under overcast, saturated conditions, while official Central Weather Administration guidance indicates slightly warmer 27–29°C night readings. This model spread, combined with the potential for localized cooling from heavy showers, explains the market’s emphasis on sub-26°C outcomes. Traders are pricing in uncertainty around the exact strength and timing of the rain event, with fresh model runs and CWA updates expected to sharpen resolution criteria before the period closes.