Evaluation of Wave Data from HF Radar by the National Weather Service

Abstract

The National Weather Service issues a marine zone forecast and surf zone forecast daily. NWS currently uses wave information collected from nearby buoys as part of the forecast process. However, the buoy data is limited in spatial coverage and are sited offshore. The Integrated Ocean Observing System (IOOS) selected a limited number of marine Weather Forecasting Offices to evaluate the utility of HF radar-derived significant wave height and direction in their marine forecasts. Wave data was provided to the National Weather Service in Mt. Holly, NJ via a web interface which allowed forecasters to view and download recent wave measurements. The wave height from the HF radar stations were compared to nearby buoys. Several wave products (individual range cell wave estimates and a composite wave product) from the HF radar were provided to the WFO for evaluation. There was good agreement between the buoys and the HF radar, especially for periods of buildings seas. However, there were instances (April 2018) where the wave height measurements from the HF radar decreased more rapidly than the wave measurements from the nearby buoys. There were also other instances of the HF radar wave heights being higher than those from the buoys. This high bias began to appear late last spring 2018 and seems to be still present in the fall. In both these cases, it is unclear at the moment if the difference we are seeing between the HF radar and the buoy is due to environmental variability or fundamental difference in how the sensors are estimating wave conditions for the area of interest. In our initial communication with the National Weather Service, the measurements from the HF radar have proved valuable to their forecast operations. We have concluded that the HF radar can provide information to bridge the gap between the buoy measurements. We will continue to explore the two measurements and look for reasons that explain the differences.