A Japanese word for August : ‘net tai ya’

Last Updated on 24.06.2022 by Coto Academy

It is well known that Japanese summer can be unbearably hot and humid, especially during July and August. All day long people will drag themselves from a building’s shadow to the cool undergrounds of Tokyo’s metro and shopping mall, resting from the heat.

One would hope that at sundown, the heat would die down… But alas! During summer, when night falls, temperatures don’t go down. This happens so often that there is a Japanese word to describe the nights during which the minimum temperature is 25 degrees or higher: 熱帯夜 (nettaiya).

Japanese DefinitionEnglish Translation
外気温が摂氏 25 度より下がらない暑い夜を日本では熱帯夜とよぶ.A hot night when the temperature does not fall below 25°C outdoors is called a ‘tropical night’ in Japan.

This Japanese word comes from “熱帯 (nettai)” meaning “the tropics”. This word relates to hot regions such as the Amazon, the Caribbean or the Philippines. The word nettai is then combined with the kanji for night, 夜 (ya). Nettaiya can be directly translated as “tropical night”, but a more accurate translation would be “sweltering night“. And it makes people miserable every summer in Japan!

According to the Japan Meteorology Agency, over 20 years the number of consecutive sweltering nights have risen to an average of 30 hot nights per year in Japan. And all of them take place during July and August.

It is said that the augmentation of hot nights is a consequence of global warming and the effects of urban heat islands. Metropolitan areas such as Tokyo stay hot during nights, due to human activity and concrete buildings. The concrete buildings absorb the heat during daytime and do not cool off at night, keeping temperature at high levels in the cities.

During the nettaiya, people suffer a lot and can hardly sleep. But even more so than the sleeping problem, nettaiya, along with natsubate (夏バテ), have proven to be dangerous, particularly to elderly people, as they increases the risk of heat stroke. There is no choice but to use air conditioning or a fan to try to refresh yourself so you can rest.

When should you use this Japanese word? Well… We can think of one really practical example! When you arrive to your work place, looking exhausted, you can just tell your colleagues that the nettaiya kept you up all night.

How to use this Japanese word in conversation?

Here’s some examples of sentences that use nettaiya!

Japanese ExampleEnglish Translation
A:おはよう。ずいぶん眠そうだね。どうしたの? A: Good morning. You look really sleepy. What’s going on?
B:毎晩毎晩、熱帯夜が続いて眠れないんですよ。B: The nettaiya keep going night after night and I just can’t sleep.
A: 大変ですね。これで 3 夜連続の熱帯夜です.A : Ah, it is hard. We had sweltering nights, for three consecutive days.
Japanese ExampleEnglish Translation
A:夏季の熱帯夜は10日ほどしかない。 A: Sweltering nights in summer season only last for about ten days.

Nettaiya may make you dream about the tropical nights at an exotic resort, but Japanese nettaiya are way different from a vacation in the tropics! Have you heard this Japanese word before? Have you experienced a nettaiya night in Japan?


Coto Japanese Academy is a unique Japanese Language School in Iidabashi Tokyo, we offer relaxed and fun conversational lessons for all levels of Japanese learner. Coto Japanese Academy prides itself on its community atmosphere and fun lessons that focus on creation of opportunities to speak and learn Japanese. If you are interested in studying Japanese in Tokyo – please visit our contact page here.