Recent ensemble forecasts from the Japan Meteorological Agency and global models indicate a Tokyo overnight minimum near 20°C on June 26, driving the narrow clustering of market probabilities around 19–22°C. Cloud cover and humidity typical of the tsuyu rainy season limit radiative cooling, while light southerly flow and possible showers maintain temperatures close to seasonal normals of 19–21°C. Minor shifts in frontal position or precipitation timing could push the low 1–2°C lower or higher, explaining the roughly equal weighting of 17–19°C outcomes and the slim tail probabilities below 17°C or above 22°C. Updated model runs and official guidance issued in the next 24–48 hours will likely refine these ranges ahead of market resolution.