Official forecasts from the Japan Meteorological Agency indicate a minimum of 19°C for Tokyo on June 18 under cloudy skies with scattered showers, consistent with mid-June climatology where overnight lows typically range 17–20°C amid the Baiu frontal zone. Market-implied odds favoring 20–21°C reflect uncertainty in model consensus on cloud cover timing and urban heat retention, which can elevate minima by 1–2°C relative to rural baselines. Key variables include evolving shower patterns that limit radiational cooling and potential shifts in steering flow; updated JMA guidance and ensemble runs overnight will clarify whether the low settles near 19°C or edges higher.