Extratropical transition of tropical cyclones over the Western North pacific. Part II: The impact of midlatitude circulation characteristics

Abstract Two characteristic midlatitude circulation patterns (labeled northwest and northeast) are found to be associated with extratropical transition (ET) of tropical cyclones over the western North Pacific Ocean. Although in both cases the tropical cyclone moves poleward ahead of a midlatitude trough, the primary midlatitude circulation is either that trough or is a large quasi-stationary cyclone to the northeast of the poleward-moving tropical cyclone. Transition into a northwest pattern typically results in the development within 36 h of an intense extratropical cyclone that moves north–northeast. A tropical cyclone that moves into a northeast pattern enters into strong zonal flow between the primary midlatitude circulation and the subtropical ridge to the southeast. These systems move rapidly eastward and do not intensify significantly during the 36 h following transition. In Part I of this study, the ET of Typhoon (TY) David (1997) and the ET of TY Opal (1997) were investigated in terms of the form...

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