 Typhoon Thad was considered the worst storm to affect Japan in two years . Originating from a monsoon trough , Typhoon Thad was first classified on August 15 , 1981 and was upgraded into a tropical storm the next day . Meanwhile , Thad moved north and northeast and attained typhoon intensity midday on August 18 . The next day , the storm reached its peak intensity of 80 mph ( 130 km / h ) . On August 22 , Thad accelerated northward , striking eastern Japan the next day just before weakening to a tropical storm . After passing through the country , the cyclone transitioned into an extratropical cyclone on August 23 . 
