We have used the potential vorticity invertibility to diagnose the typhoon track in the Western Pacific. The purposes of the paper are twofold: 1) To apply the Shapiro (1996) method to find a dynamically consistent definition of hurricane advection (steering) flow in the western Pacific where the aircraft reconnaissance plan does not exist, and 2) To quantitatively understand how individual potential vorticity perturbation associated with synoptic weather systems contributed to the typhoon motion. The knowledge of how individual potential vorticity's contribution to the typhoon track can be useful in designing ensemble forecast experiment and in designing an efficient unmanned aircraft ``aerosonde'' observational strategy. Our result for typhoon Doug (1994) indicates that the steering is best defined by the 4 to 6 latitudes ring average of flow field in the lower troposphere (surface to 300 hPa). The lower troposphere flow field, however, has an equal contribution of potential vorticity source from both the lower troposphere and the upper troposphere