One-year assessment of a nowcast/forecast system for Galveston Bay

The National Ocean Service had developed a nowcast/forecast system for Galveston Bay using a modified version of the Blumberg-Mellor (1987) three-dimensional hydrodynamic model as discussed by Schmalz (1996, 2001). The nowcast component works directly from the PORTS universal flat file format (PUFFF) files while during the forecast the NWS Aviation, River, and Extratropical Storm Surge Models are used to provide the meteorological, surface water inflow, and Gulf of Mexico subtidal water level forcings, respectively. In addition, a one-way coupled fine resolution Houston Ship Channel model (Schmalz, 2000b) has also been incorporated into the system. Daily 24 hour nowcasts and 36 hour forecasts of water surface elevation and currents, as well as near-surface and near-bottom temperature and salinity have been performed using both bay and channel models in a pseudo-operational setting since April 2000. Herein, nowcast and forecast results are assessed over the one-year period April 2000 through March 2001 based on the NOS (1999) formal acceptance statistical criteria. In general, the water surface elevation nowcast and forecast results meet or exceed the acceptance criteria except for the timings of high and low waters. For principal component direction currents, the acceptance criteria are generally met except for the timings of the zero crossings (slack before ebb and slack before flood), peak ebb, and peak flood currents. In addition, the ability of the system to forecast low water level events associated with cold frontal passages is also assessed. In conclusion, a physical interpretation of the statistical evaluation is presented and plans for additional improvements are discussed