Tropical Storm Choi-wan formed over the weekend over the open waters of the western Pacific Ocean to the east of Guam.
A strengthening trend will continue through midweek, before delivering a blast of wind and rain to northern Japan and Sakhalin.
Strengthening into a typhoon is expected within the next 12 hours then further strengthening will continue through at least Wednesday as Choi-wan moves over the open Pacific Ocean.
High pressure north of the storm will shift eastward causing Choi-wan to track northward, bypassing much of Japan.
However, a turn toward the northwest on Thursday and Friday will bring this large tropical system near or just east of Hokkaido.
Pounding rain and winds are expected across the island and neighboring Kuril Islands. Winds over 95 km/h (60 mph) are possible along with 125-250 mm (5-10 inches) of rain.
Neighboring northern Honshu can expect some strong winds and showers; however, the worst of the storm will pass to the northeast.
Choi-Wan will continue on a northwest track spreading heavy rainfall and locally damaging winds into Sakhalin Thursday night and Friday.
By the weekend, Choi-wan will interact with another storm moving over northeastern China and southeastern Russia leading to additional rainfall; however, the threat for flooding and damaging winds will be minimal.