Persistent northerly flow and widespread rain are suppressing daytime highs in Tokyo on September 11, with official forecasts and model consensus from the Japan Meteorological Agency and global ensembles pointing to a maximum of 20–22°C under overcast, showery conditions. A sharp cool-down began September 9–10 as southerly warm air gave way to northerly advection behind a frontal passage, dropping expected highs from the mid-30s°C earlier in the week to the low 20s. Cloud cover and precipitation further limit solar heating, consistent with mid-September transition patterns but cooler than the seasonal average high near 27°C. Traders have concentrated implied probability on 20–22°C outcomes because model runs show limited variability in the core daytime period, though minor shifts in frontal timing or brief clearing could nudge the peak by 1–2°C.