Latest forecasts from the Japan Meteorological Agency and global models show Tokyo’s overnight minimum on May 18 hovering near 17–19 °C, with the tight spread in trader probabilities reflecting modest differences in expected radiational cooling under partly cloudy skies and light southerly flow across the Kanto Plain. Mid-May climatology places average lows around 15 °C, so current conditions represent a mild anomaly driven by stable high pressure that limits cold-air advection and keeps surface heat retention higher than normal. Small shifts in cloud cover, humidity, or wind speed overnight can easily move the observed minimum by 1–2 °C, explaining why the 17 °C, 18 °C, and 19 °C bins remain closely matched. Updated JMA hourly guidance and Tokyo station observations on the morning of May 19 will provide the definitive reading for market resolution.