Observation Methodologies for NOAA Operational Rip Current Forecast Models

The National Weather Service and National Ocean Service, in collaboration with lifeguard agencies across the US, are using lifeguards’ rip current reports to further the vision of becoming a Weather Ready Nation. Among the initiatives made possible by these reports is the testing and implementation of a nationwide probabilistic rip current forecast model.  This model predicts the statistical likelihood of hazardous rip currents and significantly improves upon the present index-based approach used by NWS to forecast rip currents. The model has been included as a component of the Nearshore Wave Prediction System (NWPS) and is being implemented in the Great Lakes Wave (GLW) system. As part of the operational implementation, the model is being validated against rip current observations provided by lifeguard agencies at beaches along the coastal US and in the Great Lakes, working in collaboration with the NWS and NOS.  Given the hydrodynamic and rip current observations, the following methodology is applied:  1. Wave and water level model output is compared to observations where available to assess numerical model performance. 2. Lifeguard visual observations of rip current intensity are compared to rip current rescues and wave conditions to ensure quality of the visual observations. 3. The skill of the statistical rip current model is verified through comparisons with rip current observations over a range of forecast times.  This validation approach has been applied to rip current model output at Kill Devil Hills, NC, Miami, FL and San Diego, CA, with promising results. It is currently being extended to additional pilot locations.  Due to the relative scarcity of rip current reports, other sources of observation data, including archived visual observations and camera data, are also being considered. The benefits and drawbacks of the various observational approaches are discussed.