Traders heavily favor a Tokyo high of 21–22 °C on June 15 because official forecasts from the Japan Meteorological Agency and global models show a modest peak under persistent cloud cover and scattered rain tied to the onset of the East Asian monsoon (tsuyu) season. These conditions limit daytime solar heating and promote evaporative cooling, holding maximum temperatures near or slightly below the long-term mid-June normal of roughly 25 °C. Recent model runs have converged on a 21 °C high with 60–70 % probability of measurable precipitation and light southerly flow, producing the tight clustering around 21–22 °C in market prices. Stronger warming would require clearer skies or a shift in steering patterns, both of which remain low-probability outcomes in the latest guidance.