Current Japan Meteorological Agency model guidance places Tokyo’s May 17 maximum near 28–29 °C under a weakening ridge, with modest afternoon insolation and light northerly flow favoring slight warming over the urban core. The narrow spread among the 28 °C, 29 °C, and 30 °C-or-higher outcomes reflects uncertainty in exact cloud cover and the timing of any sea-breeze onset along Tokyo Bay, which can suppress the peak by 1–2 °C. Mid-May climatology at Otemachi shows a 22–24 °C average high, so today’s elevated readings stem from above-normal 500-hPa heights and reduced humidity allowing stronger surface heating. Traders are weighting the latest 12–18 UTC model runs most heavily, as any westward shift in the ridge axis or earlier marine intrusion would favor the 28 °C bin while clearer skies would push probabilities toward 30 °C or above.