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, Texas. Water surface elevation, currents at National Ocean Service prediction depth (~4.6m below MLLW) as well as near-surface and near-bottom temperature and salinity, and meteorological information are available at six-minute intervals. This real time information source is used by water resource planners and to promote safe navigation. Specifically, to complement the PORTS, a nowcast/forecast system has been developed for the Bay using a modified version of the Blumberg-Mellor three-dimensional hydrodynamic model and a one-way coupled fine resolution Houston Ship Channel model. For the nowcast, PORTS measurements are used to provide the hydrodynamic model forcings. During the forecast the National Weather Service's Aviation atmospheric and Extratropical Storm Surge Forecast Models are used to provide the meteorological and Gulf of Mexico subtidal water level forcings, respectively. The results are presented for several demonstration periods during which daily 24-hour nowcasts and 36-hour forecasts were performed using both bay and channel models in a pseudo-operational setting. The nowcast and forecast are separately evaluated for the accuracy of water levels, currents, salinity, and temperature. Evaluations of forecast Gulf of Mexico subtidal water level, freshwater inflows, and wind and sea level atmospheric pressure are also considered. In conclusion, the present system status and a strategy for continued development in a user directed GIS framework are discussed.