High-Frequency Skywave Radar Track of Tropical Storm Debra

Abstract

Tropical Storm Debra was tracked over a 31 h period in the Gulf of Mexico using the Wide Aperture Research Facility (WARF) high-frequency (HF) skywave radar in California. In contrast to the first WARF skywave radar tracking experiment in which Anita, a well-developed, intense hurricane, was positioned from the radar measurements, Debra was a weak storm with a large, poorly defined center. This data set provided the opportunity to assess the tracking capability of HF skywave radar for weak storms. Tracking began at about 1800 GMT on 27 August 1978, while Debra was a tropical depression, and continued through landfall at 0017 GMT on 29 August 1978. A smooth track was computed from seven position estimates made from radar-derived surface wind direction maps. The rms error of a third-order polynomial least squares fit to the WARF data was ±25 km. Prior to Debra's intensification to a tropical storm, the WARF skywave radar smooth track was located ?125 km west of the National Hurricane Center (NHC) smooth track. The maximum uncertainty in the WARF-derived Debra position estimates, which includes uncertainties in ionospheric height and the radar-measured surface circulation pattern, is no more than 75 km and suggests that the NHC track should be adjusted to the west. WARF radar position estimates were compared to position estimates made by NOAA reconnaissance aircraft, Galveston shore-based microwave radar, and the GOES-2 satellite for two different time periods after Debra intensified to a tropical storm. Agreement was 25, 22 and 63 km, respectively.