Latest forecast guidance from the Japan Meteorological Agency and global models places Tokyo’s May 17 maximum near 28–30 °C, producing the tight clustering of market-implied probabilities around those three outcomes. A strengthening North Pacific subtropical high is driving southerly flow across the Kanto Plain, advecting warmer maritime air while limiting cloud cover and allowing strong daytime insolation. Minor model disagreements center on the exact timing and strength of any residual marine layer or light northerly breeze that could trim the peak by 1–2 °C, or conversely on the degree of urban heat-island enhancement that could push readings above 30 °C. With resolution set by the official Otemachi observation and only hours remaining before the daily maximum, traders are weighting the most recent high-resolution runs that show surface temperatures cresting near 29 °C under mostly clear skies.