Why Is Summer in Japan So Hot? A Foreigner's Guide to Humidity and Heatstroke
.png)
“Was Japan always this hot?”
Like many countries, Japan has experienced hotter summers in recent years. News reports about record-breaking temperatures and heatstroke warnings have become increasingly common.
Before moving to Japan, I had already experienced hot summers in South Korea, so I assumed summers in Japan would feel much the same.
I was wrong.
The first thing that surprised me was not the temperature itself. It was the humidity.
Even on days when the thermometer reads 35°C (95°F), the heat can feel much more intense than the number suggests.
After only a few minutes outside, my clothes can be soaked with sweat. Even after sunset, the air often remains warm, heavy, and sticky.
After living in Japan for many years, I have realized that understanding the climate is just as important as checking the weather forecast.
If you are planning to visit Japan in summer, or if you have recently moved here, knowing why Japanese summers feel different can help you stay more comfortable and reduce the risk of heat-related illness.
Why Japanese Summers Feel Hotter Than the Temperature Suggests
Many places around the world experience higher temperatures than Japan.
Some parts of the Middle East, Southeast Asia, and the southwestern United States regularly exceed 40°C (104°F).
Yet many visitors still say that summer in Japan feels more exhausting.
After my first summer here, I realized that humidity, rather than temperature alone, was the biggest difference.
When we sweat, our bodies cool down as the moisture evaporates from our skin.
In Japan’s humid summer climate, that process becomes much less effective because the air is already full of moisture.
Instead of evaporating quickly, sweat often remains on your skin, leaving you feeling hotter and more uncomfortable.
This is also why a day around 30°C (86°F) can still feel dangerous when the humidity is high.
The temperature may not look extreme, but the body has a harder time releasing heat.
Dry Heat and Humid Heat Feel Completely Different
Over the years, I have spoken with friends from Europe, North America, and other parts of Asia, and many of them say almost the same thing after their first Japanese summer.
“I have experienced hotter weather before, but Japan feels much harder.”
I understand exactly what they mean.
In a dry climate, stepping into the shade often brings immediate relief because sweat evaporates quickly.
In Japan, summer humidity can reach 70% to 80%.
Even in the shade, the air may still feel thick and sticky.
On especially humid days, a temperature of 35°C can feel closer to 40°C or even higher because the body struggles to cool itself.
It is the kind of heat that is difficult to fully understand until you experience it in person.
How Summer Feels in Different Parts of Japan.png)
.png)
After living here for years, I have also noticed that summer does not feel exactly the same across Japan.
I currently live in Narita City, Chiba Prefecture, near Tokyo.
In the Kanto region, including Tokyo, Chiba, and Saitama, moist air from the Pacific Ocean often makes summer feel especially humid.
Large cities also experience the heat island effect. Concrete buildings and asphalt roads absorb heat during the day and release it slowly after sunset.
Because of this, nights can remain surprisingly warm, and sleeping without air conditioning may be difficult during the hottest weeks.
The Kansai region has a slightly different type of summer heat.
Cities such as Kyoto and Osaka are known for very high daytime temperatures.
Kyoto is surrounded by mountains on three sides, which can limit airflow and trap heat.
During the hottest part of summer, temperatures above 38°C (100°F) are not unusual.
| Region | What Summer Often Feels Like |
|---|---|
| Kanto | Very humid, warm nights, strong heat island effect |
| Kansai | Intense daytime heat, especially in inland basin areas |
From my own experience, summers around Tokyo often feel more humid, while Kansai can feel more intensely hot during the day.
Weather conditions change every year, but many long-term residents notice the same regional differences.
Why Heatstroke Is a Serious Concern in Japan
Every summer, Japanese news reports warn about the growing number of people taken to the hospital because of heat-related illnesses.
Heatstroke is not limited to people exercising outdoors.
It can happen while walking, gardening, working, or even staying indoors without enough ventilation or air conditioning.
Older adults and young children are especially vulnerable.
Some older people do not feel thirsty until they are already dehydrated, while children have more difficulty regulating their body temperature.
Because of these risks, schools, local governments, and businesses have become much more cautious.
Outdoor sports and school activities may be postponed or canceled based on the WBGT, or Wet Bulb Globe Temperature.
This index considers temperature, humidity, sunlight, and wind to estimate how much heat stress the body is under.
When I first moved to Japan, I had never heard of WBGT.
Now I often see it mentioned on television, weather apps, and public announcements during the hottest weeks.
Seeing those updates regularly reminded me that summer in Japan is not only uncomfortable. It can also be dangerous.
How People in Japan Stay Cool
During my first summer in Japan, one of the first things I noticed was how many products were designed specifically for hot weather.
Convenience stores, pharmacies, and home centers fill their shelves with cooling items every summer.
Common products include:
Cooling neck rings
Cooling towels
Portable fans
Salt tablets
Sports drinks
UV umbrellas
Wide-brimmed hats
I now keep several of these items at home every summer, especially cooling towels and portable fans.
They have become part of my daily routine during the hottest months.
Still, the most useful habits are often the simplest.
Drink water before you feel thirsty.
Take breaks in air-conditioned places.
Avoid spending too much time outdoors during the hottest part of the afternoon.
Do not assume you are fine simply because you have not started feeling sick yet.
Small choices like these can make a real difference.
.png)
Air Conditioning Is Part of Daily Life
Before moving to Japan, I thought air conditioning was something people used only on exceptionally hot days.
Living here changed that idea completely.
During the hottest weeks, many homes run the air conditioner for most of the day.
On especially humid days, we often leave it running much longer than we originally planned.
Electricity prices may be a concern, but air conditioning is now widely treated as part of basic heat safety rather than a luxury.
Our household is no exception.
We live with three Bengal cats, so keeping the indoor temperature comfortable is important for them as well as for us.
Every summer, they search for the coolest places in the house.
Watching them stretch out near the air conditioner is a small reminder that extreme heat affects pets too.
What Living in Japan Has Taught Me About Summer
When I first arrived in Japan, I thought the main challenge would be the high temperature.
Now I know that the combination of heat and humidity is what makes summer feel so demanding.
Over the years, I have stopped trying to tough it out.
I carry water when I go outside.
I check the forecast before making plans.
I choose indoor activities during the hottest part of the day.
If the heat feels overwhelming, I take it seriously instead of pushing myself.
After many summers in Japan, I have stopped trying to fight the weather.
Adjusting my daily routine has become the easiest way to enjoy the season more safely.
If you are visiting Japan for the first time, do not underestimate the humidity.
Light clothing, regular hydration, and planned breaks in cool places can make sightseeing much more comfortable.
Frequently Asked Questions
Why does Japan feel hotter than the actual temperature?
High humidity makes it harder for sweat to evaporate, which reduces the body’s ability to cool itself.
When is the hottest time of year in Japan?
Late July through August is usually the hottest period in most parts of Japan, although conditions vary by region.
Is heatstroke common in Japan?
Yes. Heat-related illness affects many people every summer, especially older adults, young children, and those who spend long periods outdoors.
Does Japan issue heatstroke alerts?
Yes. Weather agencies and local authorities issue heatstroke warnings during dangerous conditions and may advise people to limit outdoor activity, drink water, and use air conditioning.
Is air conditioning necessary in Japan during summer?
For many people, yes. During periods of extreme heat and humidity, air conditioning can help reduce the risk of heatstroke and improve indoor comfort.
What should visitors bring during summer?
Lightweight clothing, water, sunscreen, a small towel, and a portable fan can all make sightseeing more comfortable.
You May Also Like
If you are planning to explore Japan during the hottest months of the year, you may also enjoy my guide to Japan’s best summer festivals.
👉Japan's Best Summer Festivals: 10 Traditional Events Worth Experiencing at Least Once
Knowing how to stay cool can make it much easier to enjoy traditional events, local neighborhoods, and seasonal celebrations without exhausting yourself.
.png)
