Tropical Storm Meari will likely make landfall in Japan's central Tokai or Kanto regions on Saturday.
Authorities are urging residents to stay vigilant for landslides, flooding, high waves, and swollen or overflowing rivers.
They say heavy rain is expected to hit Shizuoka and other prefectures in the Tokai region -- raising the risk of disasters.
Officials say the storm will likely strengthen as it approaches.
Some parts of Shizuoka Prefecture have already seen more than 200 millimeters of rain in the past 24 hours.
The Tokai, Kanto and Koshin regions could see downpours of more than 80 millimeters per hour.
Officials at All Nippon Airways say they have cancelled 10 flights scheduled to leave or arrive at Shizuoka and Hachijo Island on Saturday. And they may cancel flights to and from Tokyo's Haneda Airport.
Heavy rain also persists in northern Japan. Authorities have issued an alert for Akita Prefecture.
Mudslide alerts are in place for some areas of Akita, plus Aomori and Iwate.