Traders have converged on 17°C as the lowest temperature in Tokyo on May 16 because Japan Meteorological Agency forecasts and ensemble model runs consistently projected a minimum near that value under stable high-pressure conditions with light winds and clear skies. Mid-May climatology for the Tokyo region shows typical overnight lows between 14°C and 18°C, and current observational data aligned closely with these expectations, leaving little room for significant deviation. This scientific consensus from official monitoring creates high in the outcome. A sudden shift in steering patterns or an unforecasted marine layer could still alter readings at the official station, though such changes appear unlikely given the latest model agreement.