**Market-implied odds favor a Tokyo minimum temperature of 25–26°C on August 21, 2026, reflecting typical late-summer climatology and current forecast consensus.** Tokyo’s urban heat island and high humidity (often 75–80%) keep overnight lows from dropping far below seasonal norms, with August average minima near 24–25°C according to Japan Meteorological Agency (JMA) normals. The JMA’s August 20 forecast for the 21st calls for cloudy skies and a minimum of 24°C, while other guidance (Met Office, Trip.com) points to 24–26°C amid possible scattered showers or thunder. Cloud cover limits radiative cooling overnight, supporting the market’s heavy weighting toward 25–26°C (combined ~90% implied probability), with only modest chance for a dip to 24°C if skies clear longer or rain enhances evaporative cooling. No major typhoon or anomalous circulation is currently steering the region, keeping outcomes tightly clustered around the historical baseline. Traders appear to view the JMA minimum and ensemble guidance as the primary drivers, with little evidence yet for significant deviation. Updated model runs and official JMA briefings on the 21st itself will provide the final resolution data.