Using a mass-conserving (non-Boussinesq) Pacific Ocean model and TOPEX/POSEIDON sea-surface height measurements, we document previously unreported bottom pressure waves (BPWs), associated with large-amplitude eddies (vortices) both north and south of the Equator. The bottom pressure signals, defined as the vertically integrated water-mass anomalies, are found to propagate westward across the Pacific Ocean with an approximate 4-mbar amplitude (1 mbar = 100 Newton/m2, approximately equivalent to 1 cm of sea surface height), continuously interacting with topographic features. Their wavelength is about 1100 kilometers, phase speed is about 0.5 m/s, and period is about 30-days, all consistent with the known properties of tropical instability waves (TIWs). These results suggest that the constantly evolving tropical instability eddies might have strong bottom pressure signals, therefore, likely alias the U.S.-German Gravity Recovery and Climate Experiment (GRACE) measurements, which have a monthly-sampling period.