Early June marks the start of the rainy season in Japan, known as tsuyu or baiu (梅雨, literally “plum rain”, as it coincides with the ripening of plums). Most people in Japan don't really like the rain and dread the start of tsuyu. The cloudy skies can be damper on the spirits, and the high humidity leaves many feeling more than a little irritable.
On top of that, sudden torrential rains can cause dangerous flash flooding.
— LINE NEWS (@news_line_me) June 21, 2016 
As Kyushu experiences record amounts of rainfall, three are dead and three others are missing in Kumamoto prefecture.
Heavy rains from the tsuyu monsoon front have triggered landslides in Kumamoto, which was hit by a devastating series of earthquakes in May 2016. The landslides have killed three people and left three others missing.
The rainy season is caused by the convergence of cold northerly and warm southerly air masses. A seasonal rain front (前線, senzen) moves up from the east China coast from May to mid-July each year. Okinawa—Japan's southwestern-most prefecture—experiences the rainy season first, from early May, while the Tohoku region to the northeast of Tokyo isn't hit until mid-June. Hokkaido in the far north is barely affected by the rainy season.
今日（6月21日）6～12時の降水強度の時間変化．日本付近にかかっている梅雨前線上を東進する低気圧に伴い，活発な積乱雲が観測されています．低気圧に伴う循環が降水強度でも良く現れています． pic.twitter.com/vhhDLrI6xa 
— 荒木健太郎 (@arakencloud) 2016年6月21日 
Changes in precipitation intensity from today (June 21) 6 a.m. to 12 p.m. Along with a drop in atmospheric pressure as the seasonal rain front moves east, we can expect to see active cumulonimbus clouds. The cycle brought about by the drop in pressure can be clearly observed in these patterns of precipitation intensity.
While flooding is not uncommon during the rainy season, at best the near-constant rainfall is considered to be a pesky inconvenience by most Japanese people. It's hard to dry laundry during the rainy season, and the temperature tends to fluctuate from sticky and sweltering to genuinely chilly.
It doesn't rain every day of the rainy season; however, June is known for gloomy, gray skies and predictably bad weather.
It's not all bad, though. There are some beautiful flowers that bloom during the season. Some of Japan's best scenery is even more picturesque when enshrouded in low-hanging clouds and mist.
— 土ぼっくり 6/25.26青森東北六魂祭 (@Craft_158) June 14, 2016 
Morning at Lake Gosho [in Morioka, Iwate ]
Not even a hint of a breeze to disrupt the mirror-like surface of the lake. #reflectionsinthewater #lakegosho #tsunagihotsprings
If it means we can see such beautiful clouds, I guess tsuyu isn't all that bad.
The actual amount of rainfall tends to vary from day to day, and it's not unusual for a downpour one day to be followed by occasional showers or even clear skies the next.
明るい色合いのお花をアップしてみました。 pic.twitter.com/CCCMyMbxAF 
— とうかとう(通知不具合中) (@hanazuki1949) 2016年6月20日 
Maybe it's the rain.
I'm feeling tired and down.
Have to keep my chin up.
Maybe posting these colorful flowers will help.
While grey skies can lead to low spirits, the rainy season also coincides with the blooming of beautiful hydrangeas.
埼玉県幸手市の権現堂にて。 pic.twitter.com/KCV79GwMsh 
— ゆうじ(Shiba)＠Photo (@Yuji_48) 2016年6月21日 
An elegant symbol of the rainy season.
Rain never goes where it's needed, and yet it can often be found in places that could do better without it. It's a little frustrating. How's Kanto's water shortage now?
Taken at Gogendo Temple, Satte, Saitama.
Often seen around temples in June and July, they are known as ajisai (紫陽花) in Japanese.
（ASAGI） pic.twitter.com/mxtetFYHgn 
— ASAGI_SOLO_WORKS (@ASAGI_SOLO) 2016年6月21日 
A typical rainy season sky in Tokyo today. These are some little hydrangeas I spotted on the side of the road the other day. Looking at flowers really makes me aware of the seasons! Have a great day, everyone. (ASAGI)
The flowers are native to Asia and the Americas, and can be white, blue, red, pink, or purple.
#rainyseason #rain #hydrangeas
It tends to be very hot and humid during the rainy season, but there isn't much relief to be had when it ends, as summers in Japan often reach scorching temperatures. Highs of almost 38°C (or around 100° Fahrenheit) are not uncommon for much of the country.
一日になりますように pic.twitter.com/QfOjYWE2uo 
— hazuki (@kazukihazuki) 2016年6月21日 
The color of the rainy season
Isn't it muggy?
With all this rain
Kyushu seems to be having a hard time again
I wonder if they're all right
Keep your chins up
Be true to yourselves
Don't take on too much
I hope today is a lovely day
Filled with smiles
While flooding and the resulting landslides can be a serious problem, for most people the rainy season is simply an inconvenience, and is best spent holed up indoors where it's cool and dry. Perhaps this Twitter user is onto something; riding out the sultry months inside with a cup of coffee while listening to the sound of the rain doesn't sound like a bad idea at all.
雨が傘を弾く音を聞きながら。 pic.twitter.com/6PZchQilAD 
— く～さん (@kumayairo8) 2016年6月22日 
The pitter-patter of rain
Come home at four
Sleep for an hour
Take a long shower
Coffee on the table
I savor it
Leave the house
Listen to the sound of rain bouncing off my umbrella.