The closely matched probabilities for 33°C and 34°C as Tokyo’s July 20 high reflect short-range forecast uncertainty in the Japan Meteorological Agency and ensemble guidance, with typical midsummer Pacific high pressure supporting mid-30s readings but variable sea-breeze timing and cloud cover able to trim peaks by 1–2°C. Urban heat-island effects and low-level humidity further modulate daily maxima, while recent model runs show modest spread in 850-hPa temperatures and boundary-layer mixing. Historical July averages near 31–32°C provide context, yet the market assigns meaningful weight to 32°C and 35°C outcomes because small shifts in steering flow or timing of any frontal passage could alter the peak by one degree either way before the 20th.