**Short-term forecasts from the Japan Meteorological Agency and international models place Tokyo’s overnight minimum for August 7 near 24–26 °C, producing the tight 26 °C (38 %) versus 27 °C (37.5 %) market split.** Persistent subtropical high pressure and elevated humidity limit nocturnal radiative cooling, while variable cloud cover and light winds on the forecast maps create small but decisive differences in how much temperatures fall after sunset. Urban heat-island effects in central Tokyo further compress the overnight range, keeping readings above the seasonal normal minimum of ~23.9 °C. Traders are weighting the latest ensemble guidance and any revisions to cloud or wind forecasts expected before resolution; modest shifts in these variables can easily move the recorded low across the 26–27 °C threshold.