An accidentally released drifter in the eastern section of the Strait of Gibraltar, whose successive positions were tracked bv the Argos surveillance system, was advected more than 170 km around the western Alboran gyre in the Alboran Sea of the western Mediterranean Sea during four days. The drifter trajectory along the gyre's periphery was wavelike around a hypothetical smoothed streamline, ... [Show full abstract] with a period of 35 h and an amplitude of approximately 2 km. Temperature observations confirm the wavelike nature of the trajectory. Neither tidal currents within the Alboran basin nor wind-related forcing are able to explain the observed path. The interaction of the incoming Atlantic jet and the western Alboran gyre at the place where they meet together with the existence of relative vorticity pulses of the Atlantic jet associated with tidal currents in the strait is put forward as a likely mechanism that generates short-scale eddies in which the drifter could have been trapped. The subsequent advection of such an eddy around the gyre would depict the observed wavelike trajectory.