**Forecast consensus points to a lowest temperature of 21–22°C in Tokyo on September 19, 2026, aligning closely with the market’s leading implied probabilities (49.5% for 21°C and 37.0% for 22°C).** Multiple numerical weather prediction outputs, including GFS-based guidance and Japan Meteorological Agency outlooks, indicate overnight lows in the 20–22°C range under persistent cloud cover and periods of light to moderate rain associated with a northerly flow. This setup favors radiative cooling limited by high humidity (near 85–90%) and cloud insulation rather than clear-sky extremes. Key drivers include the ongoing unsettled pattern through September 18–19, with dew points remaining elevated (around 19–21°C) and winds generally light northerly, preventing significant temperature drops. Historical mid-September baselines for Tokyo average roughly 19°C for minimums, but the current synoptic regime—marked by above-normal moisture and lack of strong cold advection—supports values 1–3°C warmer. Model agreement is high on this moderate outcome, with minimal spread across runs, which explains the concentrated trader positioning around 21–22°C and sharply lower odds for tails (e.g., 19°C or below at under 15% combined, or 23°C+ at similar levels). Upcoming JMA and ECMWF updates over the next 24–48 hours will provide the next refinement, particularly on exact timing of any clearing or additional rainfall that could nudge the overnight minimum.