Recent Japan Meteorological Agency forecasts and ensemble model runs project Tokyo’s overnight minimum on May 19 near the seasonal normal of 17–19 °C, driven by a stable Pacific high-pressure ridge that favors clear skies and efficient radiative cooling after sunset. Light winds limit mixing, while modest humidity keeps dew points supportive of lows in the upper teens. Small forecast spreads arise from uncertainties in exact cloud timing and urban heat-island intensity at the Otemachi reference station; a brief increase in low-level moisture or earlier cloud cover could hold the minimum at 20 °C, whereas sharper clearing might allow a dip to 18 °C. Updated JMA guidance issued within 48 hours will further refine these probabilities ahead of the official observation.