2026 Japan Rainy Season Forecast: Sequential Onset Followed by Record Summer Heat
Predicting the 2026 rainy season schedule in Japan. While it may resolve water shortages, heavy rain is a risk. Record heat is expected after the season ends.
The 2026 rainy season is just around the corner. According to the latest forecasts from the Japan Weather Association and others, this year's rainy season is expected to start "around average or slightly early." After it ends, there is a high probability of record-breaking heat surpassing last year. Here is the outlook from Hokkaido to Kyushu, along with key points to watch out for this summer.
2026 Rainy Season Onset and End Forecasts
Here are the predicted rainy season schedules for various regions based on the Japan Meteorological Agency's average values and the latest long-term forecasts.
Region | Predicted Onset | Predicted End |
Amami Region | May 3 (Declared) | Late June |
Okinawa Region | May 4 (Declared) | Late June |
Southern Kyushu | Around late May | Mid-July |
Northern Kyushu / Chugoku | Around early June | Mid-July |
Kinki / Tokai | Around early June | Mid-July |
Kanto-Koshin | Around early June | Mid-July |
Tohoku (Southern / Northern) | Around mid-June | Late July |
Hokkaido (Ezo Rainy Season) | Around mid-June~ | （定義なし） |
※Hokkaido has no officially defined rainy season, but tends to experience a period of gloomy weather in June known as the "Ezo rainy season."
Relief for Water Shortages vs. Caution Against Heavy Rain
Due to low rainfall since last winter, dam water levels have dropped, especially in western Japan, raising concerns about water intake restrictions in some areas. However, this year's rainy season is expected to bring active rain fronts, with precipitation forecast to be "average or slightly above average." Consequently, severe water shortages are expected to resolve.
On the other hand, the risk of "linear rainbands" causing intense rainfall in a short period is also high. While the resolution of water shortages is welcome, we must remain highly vigilant against landslides and flooding during this active rainy season.
Record Extreme Heat Fueled by "Double High-Pressure Systems" After the Rainy Season
This summer, the Pacific high-pressure system and the Tibetan high-pressure system are likely to overlap over Japan, forming a "double high-pressure system." This setup is expected to bring record-breaking extreme heat across the nation immediately after the rainy season ends.
Days with temperatures exceeding 40°C—for which the Japan Meteorological Agency introduced the term "Kokushobi" (extremely hot day)—could occur frequently, particularly in inland areas. In addition to heatstroke caused by humidity during the rainy season, preparations for health risks from intense sunlight after it ends should begin now.