Japan's Kanto-Koshin and Tokai regions officially entered the rainy season on June 7 [1].
This transition signals a period of increased precipitation that could lead to flooding and landslides across central Honshu and the southern islands. Higher-than-average rainfall is expected throughout the season, increasing the risk of natural disasters in vulnerable areas.
Weather forecaster Hoshii said rainfall is trending higher than average years [1]. This pattern is attributed to the Pacific High extending in a typical manner, which allows moist air to activate the seasonal rain front [1].
In addition to the seasonal shift, Hoshii said there is an increase in typhoon formation around the Philippines [1]. This development makes it more likely for storms to approach Japan, potentially compounding the heavy rainfall already predicted for the region.
The immediate impact of this wet weather is already being felt in the south. Authorities issued a level 4 landslide disaster warning [1] for Kunigami village in Okinawa Prefecture [1]. A level 4 warning indicates a high risk of imminent danger, requiring residents to take urgent precautions.
Forecasters are monitoring the interaction between the Pacific High and the rain front to determine the duration and intensity of the precipitation. The combination of a strong rain front and potential typhoon activity suggests a volatile weather pattern for the coming weeks [1].
“Rainfall is trending higher than average years.”
The simultaneous entry into the rainy season for two major regions, combined with an increase in typhoon activity near the Philippines, suggests a high-risk summer for Japan's infrastructure. The issuance of a level 4 warning in Okinawa highlights the immediate threat of geological instability when heavy rains hit saturated soil.
