Current Japan Meteorological Agency guidance positions Tokyo’s official minimum temperature at 18 °C on May 17, driven by a persistent high-pressure ridge that sustains southerly warm advection and suppresses nocturnal cooling across the Kanto Plain. Successive operational model runs have remained locked within a narrow 1 °C envelope, producing the market’s 99.8 % implied probability for the 18 °C bin. This consensus reflects high short-range predictability under stable synoptic conditions typical of mid-May climatology. The outcome could shift only if a late forecast adjustment or localized sensor variation at the Tokyo Haneda Airport station alters the recorded value outside the 18 °C threshold.