The motion of a growing, tropical cyclone model vortex, which is embedded in a 10 m s−1 current on an f-plane, is shown to substantially agree with the theory of vortex motion with friction (Kuo, 1969). The vortex path is trochoidal and the mean vortex motion (exclusive of the trochoidal oscillation) is about 5° to the right of the steering current (mid-troposphere current in this case). The deflection of the path is a consequence of boundary layer frictional drag forces on the vortex. The period of the trochoidal oscillation is about 15 h and the amplitude about 15 km.