The influence of mesoscale and seasonal ocean variability on three-dimensional acoustic ray paths from Heard Island through the Southern and Pacific Oceans to the California coast is investigated. For the simulation of these global acoustic ray paths, a three-dimensional Hamiltonian ray-tracing code was used. The input sound-speed fields to the acoustic ray model were interpolated from gridded temperature and salinity output data from the Semtner–Chervin eddy-resolving, global, general circulation model. The ray-tracing results have provided input to experimental planners for receiver placement off the California coast in the Heard Island Feasibility Test and shed light on the variability of the acoustic paths, insonified locations, arrival azimuthal angles, and travel times.