Extratropical Transition of Typhoon Tokage (0423) and Associated Heavy Rainfall on the Left Side of Its Track over Western Japan

Abstract

The evolution of Typhoon Tokage (0423), which made landfall in western Japan and underwent extratropical tran sition (ET) in October 2004 associated with strong winds and heavy rainfall on both the right and left sides of the storm track, is diagnosed using a gridded regional analysis (RANAL) data set produced by the Japan Meteorological Agency. When Tokage makes landfall, it is located in the right entrance of an upper-tropospheric jet streak and downstream of a synoptic-scale upper trough. The lack of an intense short-wave trough interacting with Tokage is consistent with the fact that the storm did not reintensify after the completion of ET. The strong cyclonic circulation in the lower troposphere associated with Tokage strengthens a preexisting lower-tropospheric front over western Japan, and Tokage eventually transformed into a frontal cyclone in the baroclinic zone. The conditional symmetric instability related to the approach of Tokage to the upper-tropospheric jet stream, as well as the conditional instability in the lower-tropospheric air on the cooler side of the frontal zone over the warm sea surface of the southern Sea of Japan, are considered to contribute to the heavy precipitation along the northern coast of western Japan, which is located on the left side of the storm track. Further study is needed to clarify the impact of air–sea interaction on the intensity and structure of a tropical cyclone in the midlatitude.