Using a large acoustical array located midway between Puerto Rico and Bermuda, we have observed enhanced diurnal tidal signals associated with the lowest internal-wave mode. These signals result from a diurnal internal wave resonantly trapped between the shelf just north of Puerto Rico and the turning latitude, a distance of about 1100 km. The data obtained using the large acoustical array are consistent with the predicted Airy-function variation with latitude of diurnal internal waves near the turning latitude. The existence of this wave is a striking demonstration of the long spatial and temporal coherence of oceanic internal tides. In general, the energy radiated by such waves is a loss of energy from the earth-moon system and a source of energy for mixing in the deep ocean. ¿ 1998 American Geophysical Union