The probability of Kumamoto being hit by tropical storm winds in the next 48 hours is, according to this site, fairly high. The probability of having Category 1 or higher winds, however, is fairly low (you can check that out for yourself on the web site):
http://www.tropicalstormrisk.com
Still, a slow-moving storm like this one can dump a lot of water on a place in a relatively short period of time. Even if the winds don’t seem too scary, the storm may still be quite dangerous.