Outside the hut, runoff finally flowed through dry channels that had been empty all summer.… By the third day of the heat dome, the granite ridges of the southern mountains radiated heat long after sunset. Even the cicadas had gone quiet. The six hikers had begun their traverse before dawn, intending to cross a high-altitude route that connected two aging mountain huts built during Japan’s postwar hiking boom. The route was not technically difficult in spring or autumn. In late July of 2026, under an extreme Pacific high-pressure system intensified by marine heat anomalies and stagnant atmospheric circulation, it had become something else entirely. The warning signs had been there. At the trailhead parking area, an electronic sign installed by the prefectural government flashed: WBGT DANGER — AVOID EXCESSIVE EXERTION Wet-Bulb Globe Temperature. In recent years, Japanese hiking organizations had begun emphasizing WBGT rather than ...