Evaluation of Water Level Forecast Guidance from Real Time Ocean Forecast Systems

The water level guidance, both subtidal and total, from real time oceanographic forecast modeling systems was compared to 24 National Ocean Service (NOS) water level stations on the U.S. East Coast and Gulf of Mexico Coast. The National Weather Service (NWS) Real Time Ocean Forecast System (RTOFS), the NWS Extra-Tropical Storm Surge (ETSS) Model, the United States Navy Global-Navy Coupled Ocean Model (G-NCOM), and the University of North Carolina Western North Atlantic Forecast System Advanced Circulation (ADCIRC) Model water level forecasts were compared with the observations during November 2008. Because the ETSS model is subtidal, the ETSS forecast water levels were compared with observed subtidal water levels, which were obtained using a 30 hour low pass Fourier filter. Because the RTOFS, ADCIRC, and G-NCOM include tides, their forecast water levels were compared with the total observed water level. Two new versions of RTOFS were considered and contrasted with the previous RTOFS results documented in Richardson and Schmalz (2007). Using the hourly nowcast water levels, it was possible to perform a harmonic analysis as well as a subtidal comparison using a 30 hour low pass Fourier filter with subtidal observed water levels for both RTOFS and ADCIRC. Since G-NCOM water levels were at 3-hour intervals, subtidal results could not be obtained via Fourier filter and were obtained by subtraction of the NOS predicted astronomic tide from the total nowcast water level (detiding). The evaluation demonstrates that for total water level forecast guidance, the order of skill in terms of root mean square error (RMSE) is first ADCIRC, next G-NCOM, followed by RTOFS. For subtidal water level forecast guidance, again based on RMSE, the order of skill is ETSS, ADCIRC, RTOFS, and G-NCOM. In conclusion, plans for further streamlining of the water evaluation toolset as well as the extension of the evaluation to salinity, temperature, and currents are presented.