Tokyo’s mid-June climatology, with Japan Meteorological Agency normals placing daily minimum temperatures near 19°C at this time of year, underpins the strong market consensus around a 20°C low. Current JMA and ensemble forecasts for June 18 show overnight conditions stabilizing in the 18–21°C range amid typical early-summer humidity and light winds, with no strong cold-air advection or clear-sky radiative cooling expected to push readings lower. Above-normal seasonal temperatures projected nationwide further support this narrow band. A realistic challenge would require an unforecasted frontal passage or heavier nocturnal rainfall that enhances evaporative cooling, though model consensus and short-range guidance indicate low likelihood of such deviation before resolution.