Data from current meters deployed during the CANIGO Project from June 1997 to August 1998 are analyzed. We focus on two meridionally aligned current meter moorings located west of the Portim¿o Canyon. Periodically, an XBT line was performed during the period of the current meter measurements, upstream of Portim¿o Canyon; it preceded the release of RAFOS floats in each of the two cores of the Mediterranean undercurrent, and some of these floats drifted near the current meter moorings. Two flow regimes are identified at the mooring locations: the first one is an oscillation of the velocity direction (northwest to southwest) with a regular period of about 10 days, which alternates with a second regime similar to mesoscale turbulence in which the currents flow either northward or southward during several days. The trajectories of the RAFOS floats revealed that some of them were trapped in eddies west of Cape St. Vincent when released during the first flow regime. RAFOS released during the second flow regime were trapped in coherent structures (cyclone or anticyclone) passing through or formed in the Portim¿o Canyon. The regular oscillation of the currents are analyzed in the light of the propagation of Rossby waves. First, the strong stratification above and below the undercurrent is used to diagnose the presence of topographic Rossby waves along the Iberian continental slope. Then, the observed sharp potential vorticity gradients in the undercurrent are considered in order to estimate the characteristics of vortical Rossby waves in a horizontally sheared flow. The comparison of the wavelengths for the two types of waves shows good agreement with the size of the meddies observed in the vicinity of Portim¿o Canyon and Cape St. Vincent. The waves resonant interaction leads to baroclinic and barotropic instabilities known as mechanisms for meddy formation.