**Persistent summer warmth from a strengthened Pacific High, combined with high humidity and mostly cloudy conditions, is anchoring trader expectations for Tokyo’s overnight low on August 9 near the seasonal norm of 25–26 °C.** Official guidance from the Japan Meteorological Agency and ensemble models points to a mostly cloudy night with possible rain, which limits radiative cooling and keeps temperatures from dropping sharply. Historical August lows average around 24–26 °C, but above-normal warmth this season—driven by the Pacific High extending over Honshu—has raised the floor, as seen in recent nights that bottomed near 25 °C rather than the clearer-sky dips to 22 °C earlier in the period. Urban heat retention and light southerly flow further support this range. Market-implied odds heavily favor 25–26 °C because updated short-range forecasts show little deviation from these conditions, while lower outcomes would require clearer skies or a stronger cold-air intrusion not currently indicated by model consensus. New JMA or global model runs in the next 24–48 hours remain the key catalyst that could shift probabilities.