Development of a nowcast/forecast system for Galveston Bay

The National Oceanic and Atmospheric Administration installed a Physical Oceanographic Real Time System (PORTS) in June 1996 in Galveston Bay. Water surface elevation, currents at prediction depth (4.6 m) as well as near-surface and near-bottom temperature and salinity, and meteorological information are available at six-minute intervals. To complement the PORTS a nowcast/forecast system is being developed using the Blumberg-Mellor (1987) three-dimensional hydrodynamic model. The model has been applied to Galveston Bay in support of a Differential Global Positioning System hydrographic survey (Schmalz, 1996). Herein, the grid system, boundary and initial conditions and results of the astronomical tide calibration for May 1995 will be initially reviewed. To enable a robust nowcast/forecast capability the model has been extended to include drying/wetting, and a flux corrected transport scheme to treat the large horizontal salinity gradients. The numerical algorithms for both of these extensions will be presented along with results obtained with the extended model for three one month hindcasts. Simulated water level results for the October 1994 flood and January 1995 'Northers' will first be presented, followed by simulated water level and current results for the April 1996 PORTS test period. For April 1996, results will also be presented for a one-way coupled fine resolution Houston Ship Channel model. In concert with the hindcast results, an initial nowcast/forecast system has been designed and a preliminary evaluation of system forecast inputs conducted. In conclusion, the hindcast results, initial nowcast/forecast system design, and evaluation of system inputs are reviewed and plans for additional experiments are discussed