Validation of the NOS Galveston Bay Nowcast/Forecast System Hydrodynamic Models: Review and New Perspectives

The National Ocean Service (NOS) has developed an operational nowcast/forecast system for Galveston Bay using a modified version of the Blumberg-Mellor three-dimensional hydrodynamic model extended to orthogonal coordinates by Blumberg and Herring as discussed by Schmalz. The nowcast component works directly from the National Water Level Operational Network database using standardized readers. During the forecast component the National Weather Service's North American Mesoscale, 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 higher resolution Houston Ship Channel model has also been incorporated into the system. Hourly nowcasts of the previous 24 hour period and four times daily 30 hour forecasts of water surface elevation and currents, as well as three-dimensional temperature and salinity are performed using both bay and channel models. Initially, hindcast studies over June 1995, January 1995, October 1994, and April 1996 were performed to validate the models for tidal and subtidal effects. Next, prior to operational implementation, the experimental nowcast and forecast results were assessed over the one-year period April 2000 through March 2001 based on the NOS formal acceptance statistical criteria. The methods to estimate numerical uncertainty in computational fluid dynamic computations proposed by Roache are investigated as to their appropriateness for these three-dimensional, unsteady, stratified, estuarine flow models. We first examine the basic procedures. Next we suggest how they might be applied to the bay and channel hydrodynamic model calculations. We consider both the hindcast and nowcast/forecast calculations. Potential difficulties and challenges are outlined for both calculation types. Finally, next steps are advanced to seek to improve the validation procedure.