The Japan Weather Association expects the 2026 rainy season to begin around average dates across most of the country [1].

Predicting the arrival of the rainy season is critical for agricultural planning and disaster preparedness in Japan. The timing of these seasonal rains influences crop yields and determines the window for flood mitigation efforts across the archipelago.

According to the association, the rainy season is expected to be typical for eastern Japan and the Tohoku region [3]. However, the forecast for western Japan suggests the arrival may be average or potentially early [3]. The association based these projections on analyses of precipitation and weather patterns conducted alongside the Japan Meteorological Agency [4].

As of Thursday, May 21, the official start of the rainy season has been announced only for the Okinawa and Amami regions [5]. Weather patterns on that day showed conditions improving across western Japan, while rain was expected to persist in eastern Japan and Tohoku until approximately 3 p.m. [5].

Manami Sakaguchi said, "Rain is expected to continue over a wide area moving forward" [6].

The Japan Weather Association said, "In western Japan, we expect [the start] to be average or early" [2].

Forecasters continue to monitor atmospheric pressure and moisture levels to refine the timing for the rest of the country. The transition into the rainy season often brings volatile weather shifts, increasing the risk of landslides and urban flooding in high-risk zones.

“The 2026 rainy season is expected to be typical for eastern Japan and the Tohoku region.”

A 'typical' rainy season suggests that Japan will not face an extreme anomaly in timing, but the possibility of an early start in western Japan may require local governments to accelerate drainage maintenance. Because the rainy season is the primary driver of annual precipitation, any shift toward an early arrival can disrupt the traditional planting calendar for rice and other seasonal crops.