We analyze forty-seven best-quality, ten-year-long daily Global Positioning System (GPS) position time series of Taiwan, to understand the origin of the GPS’s common-mode error (CME) whose seasonality in the standard deviation evidences a meteorological origin. We employ the efficient Empirical Orthogonal Function analysis to extract the CME as the leading island-wide mode for all three components (whereas the second mode relates to the El Niño-Southern Oscillation). We find that the CME correlates well with the acquired variations in the atmospheric mass loading (AML) displacement field for Taiwan courtesy of NASA Goddard Space Flight Center for the vertical component with high coherence around 11-14 cycles per year. Further regression analysis shows that up to 90% of the non-seasonal AML displacements in Taiwan are evident in the CME variations.