The Rainy Singularity Day (Ame no Tokuibi)

What Is "The Rainy Singularity Day"?

June 28 is known in Japan as a "weather singularity" (tokuibi) for rain -- a date that, compared with the days before and after it, sees a particular type of weather more often than chance would suggest. Based mainly on historical weather data for Tokyo, June 28 has a higher likelihood of rain than the surrounding days — in Tokyo, it is said to rain on this date 53% of the time.

Why Is June 28 Often Rainy?

At this time of year, Japan is typically in the middle of its rainy season (tsuyu), with moisture-laden air flowing in regularly and frontal activity at its peak -- conditions that favor frequent rainfall. However, being in the rainy season alone does not make a date a singularity. What makes June 28 a singularity is a statistical bias toward rain even compared with the days around it.

• A stalled rainy-season front: A seasonal rain front tends to linger over Japan for extended periods, generating rain clouds.
• Rising humidity: Warm, moist air flows in steadily from the south.
• A statistical pattern: Historical observation data shows that rainy days have been more common on this date than on the days around it, leading to its classification as a "weather singularity."

What Is a "Weather Singularity"?

A weather singularity isn't a date when a certain weather pattern is guaranteed -- rather, it's a date that shows a statistical tendency or bias compared to the average. June 28 won't necessarily bring rain every year, but historically, it has a higher-than-average chance of doing so.

• Statistical bias: Long-term data is used to identify dates where certain weather is more likely than on the surrounding days.
• Varies by region: Most of Japan's well-known singularities are based on Tokyo data, and tendencies differ by region.
• Origins of the research: Weather singularities were studied in the 1920s by the German meteorologist August Schmauss.

Fascinating Facts About the Rainy Singularity Day

• June 28 falls in the middle of the rainy season: This date coincides with a period of heavy rainfall in many regions.
• Another rainy singularity: July 17 is also a rainy singularity. Because it is the anniversary of actor Yujiro Ishihara's death, weather presenter Masamitsu Morita nicknamed it "Yujiro rain."
• Not an official designation: Singularities aren't officially designated by the Japan Meteorological Agency; the idea became widely known through weather research and media coverage.
• Sunny singularities exist too: November 3 (Culture Day) is famously known as a "sunny singularity." October 10, the opening day of the 1964 Tokyo Olympics, is sometimes called one as well, but statistically it is hard to say it is especially sunny.
• Different from a weather forecast: A singularity reflects historical tendencies, not a prediction for any specific year.

Ways to Spend the Rainy Singularity Day

• Prepare rain gear and enjoy the characteristic scenery of the rainy season.
• Review safety precautions for rainy days, such as footing and traffic safety.
• Spend time indoors with a book or a movie.
• Learn more about the meteorology behind Japan's rainy season.

Listening to the Rain Reveals the Quiet Passage of the Seasons

June 28, "The Rainy Singularity Day," is emblematic of Japan's rainy season. While rain can be inconvenient, it also connects us to the rhythms of nature. Use this day as a chance to appreciate the distinctly Japanese relationship with the rain that comes with this time of year.