Persistent heavy rain and thunderstorms across Tokyo on September 7, driven by a slow-moving low-pressure system and southerly flow, are moderating overnight temperatures and creating tight clustering in market-implied odds around 22–24°C. Official JMA guidance and ensemble models indicate a minimum near 22–23°C amid widespread cloud cover and high humidity exceeding 90%, with minor variations in shower timing and wind shifts as the primary sources of forecast spread. Traders weigh these conditions against historical September baselines of roughly 22°C overnight lows, noting that any earlier clearance or stronger advection could push the reading toward 21°C or hold it at 24°C. Updated JMA and global model runs expected overnight will likely refine the exact threshold ahead of market resolution.