Current forecast guidance from regional models indicates overnight lows in Tokyo settling near 19–20°C on May 19, driven by seasonal spring warming and southerly airflow that limits nocturnal cooling. Mid-May climatology shows average minima rising steadily from 15–16°C early in the month to 17–18°C by the third week, consistent with observed trends and the absence of cold fronts or clear-sky radiative cooling events. Urban heat retention and moderate humidity further support these values, while ensemble spreads remain narrow without major model disagreements. Traders have concentrated probability on the 19°C and 20°C bins because resolution depends on the official minimum at Tokyo Haneda, where small forecast revisions in the coming days could shift the exact reading within that narrow range.