MIE - Kuwana in Mie Prefecture recorded 40.6 degrees Celsius, the highest temperature anywhere in Japan this year, as a powerful high-pressure system and hot downslope winds combined to produce dangerous heat across a wide area.
Temperatures reached at least 40 degrees at four observation points, while 298 locations recorded highs of 35 degrees or above.
Kuwana registered the day's highest temperature of 40.6 degrees at 10:24 a.m. Other locations exceeding 40 degrees included Mino and Tajimi in Gifu Prefecture.
Reports from Kuwana showed thermometers installed beside buildings reading above 40 degrees under intense sunshine. In Gifu City, a thermometer exposed to direct sunlight appeared to be approaching 45 degrees.
Official Japan Meteorological Agency observations are taken in shaded, well-ventilated locations. Temperatures in direct sunlight, near buildings or above paved surfaces can therefore be several degrees higher than the official readings, potentially reaching 42 or 43 degrees in some places.
The widespread heat was caused in part by an unusually tall high-pressure system covering the Tokai region and western Japan.
Weather data at around the 500-hectopascal level, commonly used to assess summer high-pressure systems, showed strong descending air over areas from Tokai westward. Similar conditions were visible at the higher 300-hectopascal level, indicating that the high-pressure system extended deep into the upper atmosphere.
Air descending from high altitude was compressed as it approached the ground, causing temperatures near the surface to rise across a broad area.
Local wind conditions pushed temperatures even higher in Kuwana. Westerly winds traveled from the direction of Lake Biwa, crossed the mountains west of the city and descended toward Kuwana.
As the air flowed down the mountains, it became warmer and drier through a foehn effect, adding to the heat already generated by the high-pressure system.
The combination of widespread atmospheric compression and local downslope winds drove Kuwana's temperature to 40.6 degrees.
Dangerous heat is expected to continue in many areas through the weekend, making strict precautions against heatstroke essential.
Source: ウェザーニュース
