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What you must know about the Summer Heatwave in Japan

What you must know about the Summer Heatwave in Japantravel tips
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Many big events are held in Japan in the summer season such as traditional summer festivals, music festivals, manga&anime events, sports events, Tokyo Summer Olympics, Osaka World Expo 2025 …

There are many attractive events to visit in the summer season, however, do you know how hot it is in Japan, especially the end of July through the beginning of September?

Many international visitors have no clue how “dangerously hot” it is in Japan and they often get sick due to the heat.

I hear still some people say “I like hot, I am OK with it!”, but please take Japanese hot summer seriously!

Japanese summer weather is not dry hot, and even international residents who come from countries where is famous for hot say loudly it is extremely hot in Japan.

Today, I am going to tell you what you should learn about the Japanese summer.

“Fatal heatwave” in Japan

"Fatal heatwave" in Japan

According to data from the Fire Department, 71,317 people were urgently transported due to heatstroke nationwide from May to September 2019. This is the second number in history with 126 deaths after 95,137 in 2018. 52% of carriers were older than 65 years.

The table below shows the average temperature conditions of Tokyo, Osaka, and Kyoto during the summer months of July, August, and September in 2018.

As you see, the daily average temperatures(It is not the highest temperature!) are over 32 Celsius (91 Fahrenheit) in July and August, even in September, it is over 25 Celsius ( 77 Fahrenheit ).

The highest temperature record of this year is 40 Celsius ( 104 F ) in Niigata Prefecture, and the average high in Tokyo is 27.5 Celsius (82F) in July, 34.4 Celsius (94F) in August.

Unfortunately, the temperature like this will be new-common of the summertime in Japan.

As just looking at the number, it seems OK for you but read next carefully.

Humidity Makes Japanese Summer Worse

The high humidity of the Japanese summer also you have to be careful.

The relative humidity ranges from about 75% to 86% even on sunny days.

Summer rains are also common which makes you cooler but it will be a disaster after rains stop and the sun comes out.

Japanese summer is incredibly sticky hot. Sweating miserably and sweat never is dried up because of high humidity and crazy heat.

Do not forget to bring a towel all the time in Japan.

When my husband went to work in Japan, he got soken sweat every day. So he always brought some hand towels and an extra shirt for a change.

The Heat Island Effect

A phenomenon in which the temperature in a city becomes significantly higher than in the rural area. One of the characteristics of urban climate.

Compared to the suburbs, the center of the city is 1 to 2 degrees higher, and at night it maybe 6 or more degrees higher.

The cause is that the roads in the urban areas are paved, and also many buildings have concrete structures that make it difficult to cool even at night in the urban areas.

In addition, it is considered that a large amount of heat is artificially released by business activity such as air conditioning, Neon lights, and that the increase of high buildings in the structure weakens air circulation.

The heat island effect has been getting serious issues in such a small country, Japan, with a large population.

What International Residents Feel About The Japanese Summer

What do international residents in Japan feel about Japanese summer

Japanese worldwide clothing company, “UNIQLO” took a survey about Japanese summer from 105 international residents who live for 1 to 3 years in Japan

The result shows 73.4% of targets answered that they feel Japanese summer is hotter than their countries, included Central and South America and Africa, which are generally considered to be hotter than Japan.

According to the reason why they think Japanese summer is hotter than their countries, 62.3% of targets said: “It is very sticky hot because of high humidity.”

Get To Know About Heatstroke

The Japanese government and tourism organizations have been warning international tourists and residents about heatstroke and illness-related heat.

If you plan to visit Japan in the summer season, especially from July through the begging of September, you should learn about heatstroke.

What is heat stroke?

Heatstroke, heat exhaustion are illnesses that occur when your body gets extremely hot. The body temperature rises to 40 Celsius (105 Fahrenheit) or higher.

What happens in your body?

If you spend too much time in the heat, your body’s cooling system is not able to work properly. When your body gets dehydrated, the temperature rises and causes many illness symptoms.

what are the major symptoms?

Headache, nausea, vomiting, muscle cramps, fatigue, dizziness and more.

Be Aware With Sweltering Nights

Be aware of the high temperature and humidity even in the night.

During the summer season, the temperature doesn’t go down much as you expect and still keeps high humidity at night time.

Japanese people call “sweltering night”(Nettai Ya-熱帯夜), in which the temperature doesn’t go below 25 Celsius (77 F).

It causes “Heat Stroke” even while sleeping, and unfortunately, it happens to especially elders because they don’t have a routine to use air conditioning at home.

According to the Japan Meteorology Agency, the number of consecutive sweltering nights have been increased for the past 20 years.

The temperature, “31.3 Celsius (88 Fe), in Niigata Prefecture breaks a Japanese record of the “highest low(est) temperature” on 15 August 2019.

To prevent heatstroke while sleeping, drink a glass of water before going to bed to prevent dehydration of your body. Keep room temperature is moderate cool. If you feel too cold to use an air conditioner, Japanese air conditioners have dehumidifier function ( 除湿: jo shi tsu ).

Consider The Travel Season

I was born in Gifu Prefecture where is famous for crazy heat. My parents are still living there, but I don’t want to go back in the summer season. It is EXTREMELY HOT and I feel my body melting.

So my husband ( he sweat more than I ) and I avoid Japanese summer.

Consider visiting Japan in the summer season if you have situations below:

  • If you don’t like sticky heat
  • If you don’t like miserably sweating
  • If you have young children
  • If you are old or have older people in your company
  • if you have a chronic illness

*Heatstroke tends to occur in young children and older people because of their abilities to adjust body temperature.

In conclusion

Hoping you understood how dangerous hot in the Japanese summer season.

However, there are many things to see such as traditional summer festivals, spectacular fireworks, and beautiful mountains in Japan.

Drinking a chilled grass of chilled beer is the best part of the tradition of Japan.

Be prepared to avoid heat-related sick when you travel to Japan in the summer season, check the weather forecast every morning.

There are some apps that notify the waring of heatstroke, you can download them this site.

What you must know about the Summer Heatwave in Japan


• More details about Heatstroke; symptoms and prevention

• In case you want to know

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