In this study, we used the Navy's open domain Generalized Digital Environmental Model (GDEM) climatological temperature and salinity data on a 0.5 X 0.5 degree grid to investigate the seasonal variabilities of the southwest Philippines Sea (0.5-9 deg N, 123.5-136.5 deg E) thermohaline structure and circulation. The GDEM for the area was built up on historical (1930-1997) 10,773 temperature and 2,785 salinity profiles. A three-dimensional estimate of the absolute geostrophic velocity field on isopycnal surface was obtained from the GDEM temperature and salinity fields using the P-vector method. The seasonal variabilities of the thermohaline structure and the inverted currents such as the Mindanao Current, Mindanao Undercurrent, North Equatorial Counter Current, New Guinea Coastal Undercurrent, and dual-eddies (cyclonic Midanao Eddy and anticyclonic Halmahera Eddy) are identified.