Current ensemble forecasts from GFS, ECMWF, and JMA models indicate a daily maximum of 21–22°C for Tokyo on October 5, with persistent overcast skies, northerly winds, and limited solar heating under high pressure limiting warming. Recent observations show similar conditions yielding highs near 20–23°C, aligning with early-October climatology but tempered by cloud cover that reduces surface insolation by 30–50%. Minor model differences in timing of any patchy rain or wind shifts create the tight 44%–35% market split between 22°C and 21°C, as traders weigh resolution against JMA station data. New model runs and afternoon observations will refine this narrow range before market close.