Validating an Operational Forecast Model for Coastal Water Levels

Predictions of total water levels, which are computed as the combination of astronomical tides, storm surge, and wave runup, are necessary to provide guidance on potential coastal erosion and flooding hazards.  However, the wave runup component is presently absent from existing real-time meteorological and oceanographic forecast systems (Sullivan and Uccellini, 2013).  While some tropical storm-specific forecasts of coastal hazards exist (e.g. Stockdon et al 2012), they only consider the peak storm characteristics, do not resolve the time-varying combination of waves and water levels, and do not consider localized flooding and erosion that can happen during non-tropical or less extreme events. In response to this need, the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS) have partnered to create an operational modeling system that predicts total water level along coastal areas and therefore helps provide communities with timely coastal hazard warnings that cover a broad range of wave conditions.

The model has been successfully incorporated into an operational framework and is currently being implemented at five pilot Weather Forecast Offices (WFO’s) along the U.S. Atlantic and Gulf coasts.  Tides and subtidal water levels are provided by the Extratropical Surge and Tide Operations Forecast Systems (ESTOFS) and wave heights and periods are predicted using the Nearshore Wave Prediction System (NWPS; Van der Westhuysen et al., 2013).  Wave properties are output along the 20-meter contour and provide input for the empirical wave runup model developed by Stockdon et al. 2006.  Beach slopes, also required by the wave runup model, are calculated by the USGS using lidar topographic data.  The spatial and temporal uncertainty in total water level is also predicted.  In this talk we focus on the validation of the total water level predictions using remote sensing cameras located in some of the pilot areas.  We also assess the accuracy of the individual model inputs including wave height, period, and direction, and compare measured beach slopes to the beach slope characterization used in the operational framework.  Finally, we relate these total water level forecasts to the prediction of coastal erosion hazards.

Stockdon, H. F., Holman, R. A., Howd, P. A., and Sallenger Jr, A. H. (2006). Empirical parameterization of setup, swash, and runup. Coastal engineering, 53(7), 573-588.

Stockdon, H. F., Doran, K. J., Thompson, D. M., Sopkin, K. L., Plant, N. G., and Sallenger, A. H. (2012). National assessment of hurricane-induced coastal erosion hazards—Gulf of Mexico: U.S. Geological Survey Open-File Report 2012–1084, 51 p.

Sullivan, K. D, and L. W. Uccellini (2013). Service Assessment: Hurricane/Post-Tropical Cyclone Sandy, October 22–29, 2012, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Silver Spring, Maryland, 46 p.

Van der Westhuysen, A. J., R. Padilla-Hernandez, P. Santos, A. Gibbs, D. Gaer, T. Nicolini, S. Tjaden, E. M. Devaliere and H. L. Tolman (2013).  Development and validation of the Nearshore Wave Prediction System. Proc. 93^rd AMS Annual Meeting, Am. Meteor. Soc., Austin, TX.