Key Facts
• On September 2, 2025, Japan’s Ministry of Environment and Meteorological Agency issued a heatstroke alert for September 3.
• The alert covers 21 prefectures from Kanto to Kyushu, including Tokyo, Osaka, and Nagoya.
• Temperatures are expected to reach 38°C in Nagoya and over 35°C in Tokyo and Osaka.
• The heat index (WBGT) will rise significantly, increasing heatstroke risks in affected areas.
• Residents are advised to stay hydrated, avoid prolonged outdoor activities, and use air conditioning indoors.
• The heatstroke alert system, operational nationwide since 2021, replaces the previous high-temperature warning system.
• WBGT, an international heat index, considers temperature, humidity, radiation, and wind to assess heat risks.
• WBGT levels above 33 are classified as “dangerous,” with physical activity strongly discouraged.
• Sufficient sleep, nutrition, and salt intake are recommended for heatstroke prevention.
Summary
A heatstroke alert has been issued for September 3, 2025, covering 21 prefectures across Japan, including Tokyo, Osaka, and Nagoya. With temperatures expected to exceed 35°C in major cities and the heat index (WBGT) reaching dangerous levels, residents are urged to take precautions such as staying hydrated, avoiding outdoor activities, and using air conditioning. The alert system, introduced nationwide in 2021, highlights the importance of WBGT as a more accurate measure of heat risks compared to temperature alone. Authorities emphasize the need for proactive measures, including proper hydration, salt intake, and adequate rest, to mitigate heatstroke risks during this period of extreme heat.
