Stable high-pressure conditions and light easterly winds over Tokyo on October 15 have limited overnight radiative cooling, keeping the daily minimum in the upper teens Celsius and driving strong market-implied odds for 19°C. Official hourly observations recorded lows near 18°C in the pre-dawn hours before gradual warming under partly cloudy skies, aligning with GFS model guidance showing minimal cold-air advection. This setup matches typical mid-October climatology for the Kanto region, where average lows hover around 17–18°C absent stronger northerly flows. Traders appear to weigh the risk of a brief dip to 18°C against the likelihood of stabilization above that threshold as daytime heating begins. Final Japan Meteorological Agency verification will resolve the market once all stations report.