The operational evaluation of the Navy's globally relocatable tide model (PCTides)

The U.S. Naval Research Laboratory has developed a globally relocatable tide/surge forecast system. This system runs on a UNIX platform but was designed originally for PC-based use and is referred to as PCTides. The core of the system is a 2-dimensional barotropic ocean model. The model is forced with boundary conditions from a global tide model and uses surface winds and pressures (if available) and/or astronomical forcing. The global ocean bathymetry is a 2-minute global database developed by the Naval Research Laboratory. Atmospheric forcing from the Navy's global or regional models is provided through the METCAST system and used to generate real time, wind driven forecasts. PCTides output includes time series of tidal height deviations at each grid point of the model and time series of tidal height deviations at higher frequency (usually 10-12 minutes) at specified point locations. Barotropic tidal currents are also produced by the system. PCTides has successfully completed its operational evaluation performed by the Naval operational centers located in Norfolk, Virginia and San Diego, California. PCTides was run daily in real time to forecast tidal height deviations from regions along the east and west coasts of the United States. The model forecasts were compared to real time observations from the National Oceanic and Atmospheric Administration (NOAA) coastal tide gauges. Results from these evaluations showed an average amplitude error of 15 cm and a phase error of 30 minutes. Specific examples of PCTides hindcasts and forecasts for various areas are presented and discussed.