Data from the Ghana shelf has been analyzed to elucidate further the properties of the fortnightly wave that has been observed propagating westward along the Gulf of Guinea coast. Harmonic analysis reveals a highly coherent signal with a large quality factor Q and signal to noise ratio at the luni-solar synodic Msf fortnightly tidal frequency. The energy is trapped below the thermocline, suggestive of a topographic shelf wave. The wave is not confined to the coastal upwelling season but is manifest in the surface temperature only when the thermocline rises to the surface. Since the Rossby radius of deformation is greater than the shelf width, the model by Wang and Mooers <1976> of a hybrid topographic shelf wave modified by stratification is probably the most appropriate. The coherence and precise frequency of the wave corroborates with the suggestion by Picaut and Verstraete <1979> that the wave is induced by the Msf tide, enhanced by a nonlinear M2-S2 interaction. The eastern Gulf of Guinea is the most likely source region.