Testing An All Weather Nowcast/Forecast System for Galveston Bay

The National Ocean Service (NOS) has developed an experimental nowcast/forecast system over Galveston Bay using a three-dimensional hydrodynamic model. In addition, a one-way coupled fine resolution Houston Ship Channel model has also been incorporated into the system. 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 and the system was made operational in June 2004. To move towards an all weather capability, the following algorithms were considered and initially tested: (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, we present initial test results for Hurricane Carla in September 1961, Hurricane Alicia in August 1983, and for Tropical Storm Allison in June 2001. Longwave model results for water levels are compared with tide gauge measurements and are in agreement for peak water levels within 35 cm (~1 foot), the informal NOS target level. High water mark data comparisons are more difficult to make, since they may often include, short wave information as well. Peak current, salinity and temperature response were also simulated and areas of inundation determined, but no data are available for comparison. Similarly, short wave results for significant wave height and period are discussed in terms of representativeness since no data are available for comparison. Based on these initial test results, plans for further development and testing are advanced.