A simple coastline storm surge model based on pre-run SLOSH outputs

An empirical model to compute storm surge on open coastline for landfalling hurricanes is presented. This model uses a parametric wind profile model to compute hurricane wind speeds along coastline and an empirical wind-surge function to calculate surge heights. The wind-surge function is based on the SLOSH (Sea, Lake, and Overland Surges from Hurricanes) outputs, which have been pre-compiled by National Weather Services (NWS). Unlike the sophisticated SLOSH model, the proposed simple surge model does not involve complicated numerical computations and is easy to use, though it takes advantages of SLOSH model's accuracy. In addition to estimating surge heights for individual hurricanes, this model can be used to assess coastal surge risks by simulating efficiently a large number of hypothetic hurricanes.

The key element of the model is the approximation of wind surge function based on SLOSH output MEOW (Maximum Envelope of Water). The MEOW is one of the SLOSH composites in a SLOSH Display package generated by NWS for local evacuation planning, which were derived by simulating thousands of hypothetical hurricanes at each basin. Each MEOW is generated with a group of parallel hurricanes about 10 miles apart with specified hurricane parameters, including hurricane category (1 to 5). As an approximation, surge height at a given coastline location is assumed as a function of wind speed at the location and other variables such as storm direction at landfall, translational speed , initial tide level, and local geographical conditions. The actual form of the general function is unknown and could be extremely complex. The five MEOW surge heights for each of the five hurricane categories at a given location are assumed to be five samples of the wind-surge function. These five samples, corresponding to the wind speeds of each hurricane category that are converted from the central pressures by a pressure-wind relationship, are linearly interpolated to approximate the wind-surge function. The wind profile model is a modification of Kaplan-DeMaria empirical wind model for coastline locations.

This model has been compared to SLOSH model with computed storm surges for three hurricanes making landfall in three separate SLOSH basins. On average, the surge heights computed by the proposed model are about 15% percent of the values by SLOSH model. Figure 1 shows an example of the comparison for 1989 Hurricane Hugo.

                   

Figure 1. Comparison of surge heights by SLOSH and surge heights by the simple  model for 1989 Hurricane Hugo.