**Forecast consensus from multiple models and official guidance points to a minimum temperature of 19°C in Tokyo on September 27, 2026, driving the 84% market-implied probability for that outcome.** Overcast skies, light northerly winds, and scattered drizzle or showers overnight are expected to moderate radiative cooling, keeping the low near the seasonal norm of approximately 18°C rather than allowing deeper drops. Recent JMA and global model runs (GFS, ECMWF) show early-morning readings stabilizing around 18–19°C after daytime highs near 23–24°C, with no strong cold-air advection or clear-sky conditions to push readings lower. Historical late-September lows average 18–20°C, providing a stable baseline that reinforces trader confidence in the narrow 18–19°C range. The 10% probability on 18°C and 5% on 17°C reflect residual model spread and the chance of slightly stronger cooling if winds weaken further, while probabilities below 17°C remain negligible absent an unexpected frontal passage. Updated forecasts through the evening of September 26 will be the key near-term catalyst for any final shifts in implied odds before resolution.