Japan Issues Heat Stroke Alerts for 41 Prefectures as Extreme Heat Grips Nation

On Tuesday, August 25, 2026, Japan’s Ministry of the Environment (MoE) and the Japan Meteorological Agency (JMA) issued heat stroke warning alerts — known in Japanese as netsuchūshō keikai arāto — for 41 of the country’s 47 prefectures, stretching from Tohoku through Kyushu. Officials warned that a dominant Pacific high-pressure system and unusually warm air aloft would push daytime highs toward 40°C (104°F) in parts of southwestern Japan, with dangerous heat expected across much of the archipelago.

Editor’s note: This article draws on JMA forecasts, MoE heat-illness prevention guidance, NHK World reporting, Weather News, and Asahi Shimbun coverage, August 25, 2026. Alert status and temperature forecasts are updated on official MoE and JMA channels.

Which areas are under alert?

The Heat Stroke Alert was in effect across 41 prefectures on August 25, according to MoE and JMA announcements reported by Weather News and NHK. The alert zone runs from Iwate in northern Honshu southward through the Kanto, Chubu, Kinki, Chugoku, Shikoku, and Kyushu regions.

Region	Prefectures under Heat Stroke Alert (Aug. 25)
Tohoku	Iwate, Miyagi, Fukushima
Kanto / Koshin	Ibaraki, Tochigi, Gunma, Saitama, Tokyo, Chiba, Kanagawa, Yamanashi
Tokai / Hokuriku	Shizuoka, Aichi, Gifu, Mie, Niigata, Toyama, Ishikawa, Fukui
Kinki	Shiga, Kyoto, Osaka, Hyogo, Nara, Wakayama
Chugoku / Shikoku	Okayama, Hiroshima, Shimane, Tottori, Tokushima, Kagawa, Ehime, Kochi, Yamaguchi
Kyushu	Fukuoka, Oita, Nagasaki, Saga, Kumamoto, Miyazaki, Kagoshima (excluding the Amami Islands)

Six prefectures were not covered by the August 25 alert, including Hokkaido, Aomori, Akita, Yamagata, and Okinawa — areas where weather conditions differed. Hokkaido and parts of northern Tohoku faced unstable atmospheric conditions from a low-pressure system and frontal activity, with localized heavy rain, landslide risk, and lightning through Tuesday night, JMA said.

Japan is divided into 58 regional forecast units for heat alerts; the MoE publishes status maps and updates at 5:00 a.m. and 5:00 p.m. daily during the alert season (late April through late October).

Forecast temperatures: where the heat peaks

JMA daytime high forecasts for August 25 pointed to widespread mōsho (extreme heat) conditions:

Forecast high	Representative cities
40°C	Kumamoto, Hita (Oita), Kurume (Fukuoka)
39°C	Kyoto, Kumagaya (Saitama), Saga
38°C	Nara, Maebashi (Gunma)
37°C	Nagoya, Hiroshima
36°C	Osaka, Sendai, Takamatsu
35°C	Central Tokyo and other areas

NHK noted that Kumamoto Prefecture — still recovering from a powerful earthquake in late July — was among the areas facing the most intense heat. Weather News reported that temperatures in alert zones could exceed body temperature, creating conditions where heat illness risk rises sharply even before midday.

JMA forecasters said eastern and western Japan are likely to remain under prolonged high temperatures in the coming weeks, extending a punishing late-summer heat pattern.

How the Heat Stroke Alert system works

Japan’s Heat Stroke Alert (netsuchūshō keikai arāto) is a joint MoE–JMA public-health warning distinct from ordinary high-temperature advisories. It is triggered when the forecast Wet Bulb Globe Temperature (WBGT) — a heat-stress index that accounts for temperature, humidity, and solar radiation — is expected to reach 33 or higher in a given region.

Element	Detail
Trigger	Forecast WBGT ≥ 33
Issuing bodies	Ministry of the Environment + Japan Meteorological Agency
Geographic units	58 regions nationwide
Update schedule	5:00 p.m. the previous day; 5:00 a.m. the same day
Season	Fourth Wednesday of April through fourth Wednesday of October

A more severe tier, the Special Heat Stroke Alert, is issued when WBGT is forecast at 35 or higher. On August 25, MoE data showed no Special Heat Stroke Alerts nationwide, but standard alerts covered the 41 prefectures listed above.

The MoE operates a dedicated heat illness prevention portal (wbgt.env.go.jp) with regional WBGT forecasts, alert maps, and prevention guidance in Japanese and English.

Official safety guidance

MoE, JMA, and NHK urged residents — especially older adults, outdoor workers, children, and people with chronic illness — to take active precautions:

Stay cool indoors

• Use air conditioning rather than relying on fans alone when indoor temperatures are high.
• Avoid prolonged outdoor activity during peak heat hours; schedule errands for cooler parts of the day.

Hydration and salt

• Drink water frequently, even if not thirsty.
• Replenish salt lost through sweating — especially for people working or exercising outdoors — following general dietary guidance and any personal medical restrictions.

Watch vulnerable neighbors

Officials emphasized checking on elderly relatives and neighbors, who face disproportionate heat-stroke risk. Adequate sleep and nutrition are also cited as baseline prevention measures.

Recognize warning signs

Seek medical help promptly for symptoms such as dizziness, headache, nausea, rapid heartbeat, confusion, or hot dry skin. Heat stroke can progress quickly and is potentially fatal without rapid cooling and treatment.

Broader context: a nation under sustained heat

The August 25 alerts cap a summer in which Japan has repeatedly faced record or near-record heat. Pacific high pressure has parked over the main islands for extended periods, while very warm air in the upper atmosphere has amplified surface temperatures from morning onward.

In Kyushu, the combination of post-earthquake recovery demands and extreme heat has added strain to communities still managing infrastructure repairs and displacement from the July quake. In Kanto, forecasters noted that coastal Pacific areas could see 35°C or higher for the first time in weeks.

Meanwhile, the contrasting weather in Hokkaido and northern Tohoku — heavy rain, swollen rivers, and landslide watches — illustrates how Japan can experience simultaneous heat emergencies in the south and flood risks in the north during late August.

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Discussion

1. Does your household treat air conditioning as essential safety equipment during heat waves — or as a luxury to minimize?

In Japan and elsewhere, energy costs and cultural habits shape how people respond to official heat alerts. Where do you draw the line between saving electricity and preventing heat illness?

2. Who checks on the most vulnerable people in your community when alerts like this are issued?

Elderly residents living alone face the highest heat-stroke mortality in many countries. Are neighbor networks, municipal cooling centers, or family routines enough — or should governments do more?

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This article is news and general health information, not personal medical advice. If you or someone nearby shows signs of heat illness, seek professional care immediately.