Divergent ensemble forecasts from the Japan Meteorological Agency and global models create tight clustering around 30–32°C for Tokyo’s August 19 maximum, reflecting uncertainty in cloud cover, convective timing, and insolation under the subtropical Pacific high. Mostly cloudy conditions are expected to moderate peak heating, yet small shifts in sea-breeze onset or urban heat-island amplification—driven by impervious surfaces and low wind—could easily differentiate outcomes by 1–2°C. Historical August normals near 31°C provide context, while ongoing above-average seasonal warmth adds slight upward pressure without clear extremes. Updated JMA guidance and model runs over the next 48 hours will likely sharpen resolution criteria around observed daily highs.