In order to examine the percentage of appearance of the typhoons which have the maximum wind speed in their navigable (left) semicircle, typhoons of 2001 through 2005 are statistically analyzed using the Japan Meteorological Agency Best Track and Mesoscale Analysis data. As a result, 31% of all the typhoons are found to have the maximum wind speed in their left semicircle. The percentage tends to be higher with progress of season, reaching up to 44% in October. It is moreover found that the percentage is greater for eastward-moving typhoons and for those with a traveling speed of over 40km/h. These results indicate that the transition process of a typhoon to an extratropical cyclone is one of the main causes for the appearance of the maximum wind speed in the left semicircle. Thus, this paper finally suggests that caution should be exercised for the left semicircle of the typhoon which approaches to Japan in late autumn, moving eastward at a high speed.
