Coupling a Rip Current Forecast Model to the Nearshore Wave Prediction System

Rip currents are the leading cause of fatalities and rescues along beaches in the United States. The United States Lifesaving Association (USLA) estimates that nearly 100 fatalities per year occur in the U.S. due to rip currents. Rip current forecasting methods have remained relatively unchanged over the past 20 years and do not take advantage of recent advances in nearshore wave monitoring and modeling. A probabilistic rip current forecast guidance model has been created to predict the likelihood of hazardous rip current occurrence given wave field and water level inputs. The model was developed through a logistic regression of wave and water level observations with lifeguard observations of rip current occurrence and intensity. An initial assessment indicated the model outperformed the present index-based methods used by the National Weather Service (NWS; Dusek and Seim, 2013). Model inputs are provided by the NWS Nearshore Wave Prediction System (NWPS) which is presently being incorporated at Weather Forecast Offices (WFO) nationwide (Van der Westhuysen et al., 2013). The output is the percent likelihood of hazardous rip current occurrence at a resolution of ~1 km along the coast. The performance of the rip current forecast model is presently being tested operationally at the WFO in Morehead City, NC (MHX) for two locations on the Outer Banks - Emerald Isle and Kill Devil Hills. Lifeguard observations of rip currents are being collected concurrently with the model output, and will be used to determine forecast skill. In 2014, the model will be tested at additional locations in the WFO MHX area of forecast responsibility and at other WFOs to assess the portability of its underlying parametric expressions. An improved rip current guidance system will benefit both lifeguards and beachgoers throughout the United States. This system will translate into more effective outlooks and statements issued by the NWS and aid in reducing the large number of rip current-related rescues and fatalities.