We show that the transpacific expendable bathythermograph data of the North Pacific Experiment (NORPAX) contain annual temperature disturbances that propagate along the Subtropical (32 ¿N) and Subarctic (42 ¿N) fronts in the central North Pacific. We find these disturbances in the depth range 150--400 m. They propagate with phase speeds of between 10 and 20 cm s-1, and they reverse their direction of propagation with an annual cycle. We present a possible explanation of this phenomenon in terms of baroclinic Rossby waves in flow with vertical and lateral shear.