Towards An All Weather Nowcast/Forecast System for Galveston Bay

The National Oceanic and Atmospheric Administration has developed an experimental nowcast/forecast system over Galveston Bay using a modified version of the Blumberg-Mellor three-dimensional hydrodynamic model as discussed by Schmalz. In addition, a one-way coupled fine resolution Houston Ship Channel model has also been incorporated into the system. The nowcast component works directly from the PORTS universal flat file format (PUFFF) files, while during the forecast the NWS Aviation and Extratropical Storm Surge Models are used to provide the meteorological and Gulf of Mexico subtidal water level residual forcings, respectively. Nowcast and forecast results have been assessed over the one-year period April 2000 through March 2001 based on the NOS formal acceptance statistical criteria. Event analysis was also performed for both water levels and principal component direction currents. For water levels, a majority of the formal acceptance targets were met and considerable skill was achieved in forecasting low water level events associated with winter cold frontal passages. Currents were more problematic especially at Morgans Point at the head of the Bay, where rainfall/runoff flows exhibit considerable impact on currents within the Port of Houston. To improve the current response and to move towards an all weather capability, the following processes have been considered: 1) rainfall/runoff inflows from four major basins within the City of Houston, 2) overland flooding, 3) tropical storm and hurricane wind and pressure fields, and 4) surface waves. Herein, the algorithms used to describe each of the above processes are first developed. Next, the design of the all weather nowcast/forecast system is presented. Initial test plans for Tropical Storm Allison in 2001 and for more extreme storms are then discussed. Finally, future enhancements of a generalized vertical coordinate and incorporation of wave/current interactions are outlined.