Traders assign the highest implied probabilities to a Tokyo minimum temperature of 27–29°C on July 31 because ensemble forecasts and climatological normals place the daily low in that narrow range during peak summer. Persistent high pressure and warm, humid air masses advected from the Pacific maintain overnight temperatures near or slightly above seasonal averages of 24–26°C, while urban heat retention limits radiative cooling. Short-range model runs show limited day-to-day variability, keeping probabilities for outcomes below 25°C or above 30°C well under 30%. New Japan Meteorological Agency guidance and updated numerical weather prediction output expected within 48 hours will determine whether any coastal breeze or increased cloud cover shifts the minimum by 1–2°C.