Experimental Galveston Bay/Houston Ship Channel Nowcasting/Forecasting System

The data delivery system consists of the Operational Data Acquistion and Archive System (ODAAS) maintained by the NOS Coast Survey Development Laboratory (CSDL) in which NWS Aviation Model wind/pressure fields are automatically downloaded to CSDL machines. Additional scripts decode NWS Extra-Tropical Storm Surge water levels at Galveston Pleasure Pier. The NWS Western Gulf River Forecast Center (WGRFC) uploads to CDSL anonymous ftp, three day 6 hour interval forcasted river flow and stage for the Trinity River at Liberty , Texas and Lake Houston Dam near Sheldon, Texas, respectively. In addition, the previous day's hourly discharges at Liberty, Texas on the Trinity River and at Piney Point, Texas on Buffalo Bayou and stage for Lake Houston Dam near Sheldon, Texas are uploaded. A decode script accesses and decodes the Houston/Galveston PUFFF water level and current meter files every 6 minutes and stores daily station files.

The hydrodynamic component consists of a three-dimensional sigma coordinate Galveston Bay and near shelf model (GBM) based on a version of the Blumberg and Mellor (1987) model extended to orthogonal curvilinear coordinates by Blumberg and Herring (1987). The GBM computational grid consists of 181x101 horizontal cells (dx = 254-2482m, dy= 580-3502m) with 5 levels in the vertical.

To simulate currents within the Houston Ship Channel (HSC), a fine resolution channel model (HSCM) was developed. The refined channel grid was developed in three sections, which were linked in order to develop the final composite channel grid consisting of 71 x 211 horizontal cells (dx=63-1007m, dy=133-1268m) with the same 5 sigma levels as in the GBM. The entrance section resolution in the refined grid represents an order 3 increase in resolution over the Bay grid. The two models are then nested in a one-way coupling scheme, wherein GBM water surface elevation, salinity, temperature, turbulent kinetic energy, and turbulent length scale time histories are saved at 6-minute intervals to provide boundary conditions to drive the HSCM.

An initial design of a nowcasting/forecasting system has been completed. The design concept is modular such that refined hydrodynamic models can be readily substituted for the initial models. To this end, a separate nowcast/forecast program has been developed to establish hydrodynamic model forecast inputs. The program utilizes the following ten step procedure:

1. Setup 24 hour nowcast and 36 hour forecast time periods,
2. Predict astronomical tide,
3. Predict astronomical currents,
4. Read PUFFF files and develop station time series,
5. Develop GBM subtidal water level signal,
6. Assimilate PORTS salinity and temperature data into GBM and HSCM initial conditions,
7. Establish GBM and HSCM salinity and temperature boundary conditions,
8. Establish GBM and HSCM SST forcings,
9. Establish USGS observed and NWS/WGRFC forecast freshwater inflows, and
10. Establish PORTS based and Aviation Model wind and pressure fields.

Time series files for predicted water surface elevation, and principal direction prediction depth currents are generated as well as PORTS time series data files for water levels, currents, salinity, temperature, wind, and atmospheric pressure. Time series analysis programs to plot nowcast and forecast results in conjunction with the above time series files for both models have also been incorporated within the system.

Last updated on February 5, 2001