Jangmi made landfall in southern Wakayama around 4:30 a.m. Wednesday after lashing western Japan, with maximum winds of 126 kph as it moved east-northeast at 40 kph.
A level 5 flood danger warning — Japan's highest — was issued for the Koza River after it began overflowing, and residents nearby were urged to take maximum caution.
The Japan Meteorological Agency had already detected a linear rainband over southern Wakayama, signaling extremely heavy rainfall and the risk of further flood and landslide disasters.
Up to 200 millimeters of rain is forecast through 6 a.m. Thursday in Tokai and Kanto-Koshin, with up to 120 mm in Tohoku as the typhoon tracks east along the Pacific side.
Before landfall, Jangmi brushed Kyushu and Shikoku, where level 4 flood warnings were issued for rivers in Miyazaki and Tokushima, underscoring the storm's widening impact.