Rain is expected to spread from the west across Japan on Wednesday, May 20 [1].
The shift in weather follows a period of intense heat that saw 706 locations nationwide record a summer day of 25 degrees Celsius or higher [1]. The incoming rain is expected to cool the atmosphere after several regions experienced sudden spikes in temperature.
According to the Japan Meteorological Agency and affiliated services, a stationary Baiu front is lingering over southern Japan [1]. This system is bringing moisture from the west that will cause precipitation and lower temperatures across the archipelago [1].
The rain is projected to move eastward in stages throughout the day. Forecasts indicate rain will begin in Kyushu during the morning, moving into Chugoku, Shikoku, and Kinki by midday [1]. The system is expected to reach Tokai in the evening and arrive in Kanto and the Hokuriku/North Alps region by night [1].
Forecasters are monitoring southern Kyushu, including Kagoshima, for a potential early start to the rainy season [1]. The average date for the start of the rainy season in southern Kyushu is typically around May 30 [1].
The timing of this transition follows extreme heat in some northern areas. For example, the maximum temperature in Fukushima recently reached 35 degrees Celsius [1].
Weather forecasters said that while it feels as if midsummer has suddenly arrived, the rain moving in from the west should cool the air.
“Rain is expected to spread from the west across Japan on Wednesday, May 20.”
The potential for an early onset of the rainy season in southern Kyushu suggests a deviation from historical meteorological patterns. When combined with the recent extreme heat recorded in Fukushima and other regions, these fluctuations indicate a volatile transition into the summer months that could impact agricultural planning and disaster preparedness for seasonal flooding.
