Japanese weather officials say a low pressure system will likely bring localized torrential rainfall to wide areas across Japan.
They are warning that the risk of flooding could increase in areas hit by Typhoon Hagibis.
The Meteorological Agency said on Thursday that heavy rain has fallen intermittently in many parts of western Japan due to a low pressure system staying near the Kyushu region.
The system is expected to move toward western and eastern Japan on the Pacific coast, causing atmospheric conditions to become unstable across wide areas.
The agency says extremely heavy rain accompanied by thunder may fall in western Japan through Friday morning.
Downpours are expected in some parts of eastern Japan early on Friday morning through the night and in Pacific coastal areas in the Tohoku region between Friday afternoon and Saturday morning.
Rainfall in the 24 hours through Friday evening could reach 300 millimeters in the Tokai region, 250 millimeters in the Kinki and Shikoku regions, 200 millimeters in the Kanto region which includes Tokyo, and up to 100 millimeters in the Tohoku region.
The agency is warning that very strong Typhoon Bualoi will likely reach the sea off the east coast of Japan on Friday, and the sea near the Kanto and Tohoku regions could become very rough.