Get ready for rainy season in Japan

“It’s just weather!” Sounds like the kind of mantra reeled off by an overzealous lead rambler addressing their reluctant charges in a muddy field halfway through what has turned out to be a soaking wet Sunday afternoon slog somewhere back home on the British Isles.

Perhaps the equivalent and suitable timing to vocalize the hopeful sentiment here in Japan would be during the rainy season. Maybe sometime during day five into what could turn out to be a 10-day block of morbidly gray skies and persistent rain. Chin up, it’s just weather.

Rainy season, or tsuyu, the seasonal phenomenon which marks the transition from spring to summer in Japan. Locals sometimes introduce it with inexplicable glee to the unsuspecting, or by now uninterested, foreigner as Japan’s “fifth” season. 

“Actually, Japan has five seasons,” as a common refrain sounds almost as tired as, “you're good at using chopsticks,” and maybe even carries the same potential to infuriate the listener as, “it’s just weather.”

It might only be weather but Japan’s rainy season has the potential to feel like a drag. 

In an average year, the rainy season starts at the end of May in parts of southern Kyushu, before arriving in Osaka and Kyoto, and the wider Kansai region, around June 6, with Tokyo, and the wider Kanto-Koshin region, soon to follow around June 7, according to the Japan Meteorological Agency.  

When it reaches northern Tohoku in the middle of June, the whole country could be said to be cloaked in the drab colors of the season, except Japan’s northernmost prefecture of Hokkaido which is spared of the phenomenon. 

Japan begins to emerge from the rainy season around one month later, starting in southern Kyushu around June 29. Other regions take a little longer to dry off. Rainy season ends in Osaka and Tokyo (and the wider Kansai and Kanto Koshin regions) around July 19, and in northern Tohoku around July 28.  

The rainy season of 2023 arrived earlier than usual in most regions of Japan. Unfortunately for some though, this didn’t mean an earlier departure. 

When does rainy season in Japan start and end?

The following chart shows the average start and end dates of the rainy season across regions of Japan as well as those dates for 2023. The chart below was reproduced from a chart published by the Japan Meteorological Agency.

Continued:

This is not to say that it is wet and cloudy everyday throughout the rainy season, but there can be times when it feels unending.

The rainy season of 2019 in Tokyo and the wider Kanto-Koshin region, for example, was longer and wetter than usual. What turned out to be a 52-day season saw a stretch of almost 20 days averaging less than three hours of sunlight per day. In some cities east of Tokyo the amount of rainfall during the same season reached over 400mm and in one city topped 500mm. In a typical year the region will see around 300mm of rain during the season.

While we might try to lighten the damp mood that the rainy season brings, the dangers of flooding, burst river banks, and landslides, among other consequences of the rainfall, are very real.  

Rain fronts remaining stagnant over parts of western and southwestern Japan, in particular, can bring heavy rainfall resulting in flooding and landslides. The kind of rainfall that might be experienced in Tokyo over an entire season can be dumped in a single day in parts of western and southwestern Japan. During the last rainy season the city of Kurume in Fukuoka Prefecture saw 402.5mm over a 24-hour period, the highest amount recorded in the city, according to reports.

During the rainy season people in Japan should pay attention to weather agency warnings and government advisories, sometimes even orders, to evacuate. 

Fortunately for most people, the rainy season in Japan is probably at its worst nothing more than a source of irritation. Even if the rain isn’t particularly heavy, or maybe doesn’t fall at all on a given day, the sense of things being wet and damp can be all-consuming. 

Jimejime (じめじめ or ジメジメ) is a term often heard during rainy season, used to describe a sense of uncomfortable humidity, of being sticky or muggy. The feeling can become more of an irritation given that the perceived temperatures of the season can be hard to pin down - it’s not particularly warm, it may even be a little cool, and yet somehow that easy five-minute walk to the train station has me all in a sweat!

This is where clothing can become a challenge - waterproof layers may keep the rain out, but they’ll bring out the sweat and give resulting odors nowhere to go, until they can be let loose, sometimes within the confines of a train and on fellow commuters already feeling damp and irritable. Umbrellas and increasingly, as well as increasingly fashionable, rain boots are the order of the day. 

However irritating the rainy season in Japan can feel, try to remember that it serves the important function of building up the water supply ahead of potential shortages over the summer. And almost as quickly then, try to forget that it is the lead into summer, arguably the most testing of Japan’s seasons.  

Get ready for rainy season in 2024, and maybe even enjoy it, with the tips, advice, and experiences of the City-Cost community.