Tropical season is in full swing in the West Pacific, as evidenced by the three tropical storms currently spinning in the basin.
Tropical Storm Mindulle is the strongest of the three and is the storm expected to strengthen into a typhoon in the next day or two.
"The biggest threat to the Japanese mainland will be the storm farthest away currently, as Tropical Storm Mindulle will approach southeast Honshu early next week," AccuWeather Meteorologist Eric Leister said.
Mindulle will undergo steady intensification in the next 24 to 48 hours as it moves over warmer ocean waters and encounters weaker upper level winds.
Eastern Honshu will begin to feel impacts from Mindulle on Monday morning, local time. Conditions will worsen as the typhoon makes landfall southwest of Tokyo Monday night into Tuesday.
The main threats from Mindulle will be flooding rainfall, with widespread amounts of 100 to 150 mm (3 to 6 inches) expected from Tokyo to Sendai and up to Sapporo. Locally higher amounts are possible from the heavier rain bands.
Residents should be on alert for the potential for mudslides and take precautions when driving in areas that may be flooded.
Mindulle will pack sustained winds of 130 km/h (80 mph) and gusts up to 160 km/h (100 mph). The strongest wind gusts will be along coastal regions.
There are two other tropical systems that could post a threat to parts of Japan.
Tropical Storm Kompasu is situated well east-northeast of Yokosuka, Japan, and will slowly make a turn to the northeast on Sunday.
"A landfall is possible on Saturday night or Sunday morning in northern Honshu. The storm will bring locally heavy rainfall and gusty winds to northern Honshu and eastern Hokkaido," AccuWeather Meteorologist Eric Leister said.
This first round of flooding on Sunday could set the stage for an enhanced flood risk from Mindulle when it moves through late Monday into Tuesday.
The final storm, Tropical Storm Lionrock, is located several hundred miles southwest of Tokyo and is expected to drift slowly to the west-southwest before stalling near the Ryukyu Islands.
Tropical Storm Lionrock could intensify into a typhoon next week and bring flooding rain and damaging winds to the Ryukyu Islands.