Recent Japan Meteorological Agency forecasts position Tokyo’s May 17 maximum near 28–29 °C at the Otemachi station, driven by a high-pressure ridge that favors southerly warm advection and strong afternoon insolation under mostly clear skies. These conditions explain the tight clustering of market-implied odds around the 28 °C, 29 °C, and 30 °C-or-higher outcomes, each near 27–29 percent. Historical May averages at the site run 22–24 °C, so the current setup represents a modest but measurable departure above the climatological baseline. Minor shifts in ridge strength or timing of any late-day cloud cover could still nudge the official high across the 29–30 °C threshold before resolution.