Forecast models from agencies including the Japan Meteorological Agency indicate clear to partly cloudy conditions over Tokyo on October 17, supporting overnight radiative cooling that favors a daily minimum near 17–19 °C. Light northerly to easterly winds and surface high pressure limit advection of cooler air, while dew points around 10–13 °C constrain further temperature drops. Recent October warmth, with observed lows of 15–19 °C through mid-month, reinforces this range amid a +2 °C seasonal anomaly. The near-even market pricing between 18 °C and 19 °C (both 42.5 %) reflects small divergences among ensemble runs on exact cloud cover and wind speed, with lower outcomes priced lower due to limited evidence for stronger cooling. Updated model guidance ahead of the date will be the key near-term driver.