Influences on Observed Near-Surface Gust Factors in Landfalling U.S. Gulf Coast Hurricanes: 2004–08

Abstract

he deployment of ruggedized surface observing platforms by university research programs in the path of landfalling tropical cyclones has yielded a wealth of information regarding the near-surface wind flow characteristics. Data records collected by Texas Tech University?s Wind Engineering Mobile Instrument Tower Experiment and StickNet probes and by the Florida Coastal Monitoring Program along the Gulf Coast of the United States from 2004 to 2008 were compiled to examine influences on near-surface gust factors. Archived composite reflectivity data from coastal WSR-88D instruments were also merged with the tower records to investigate the influence of precipitation structure. Wind records were partitioned into 10-min segments, and the ratio of the peak moving-average 3-s-gust wind speed to the segment mean was used to define a gust factor. Observations were objectively stratified into terrain exposure categories to determine if factors beyond those associated with surface frictional effects can be extracted from the observations. Wind flow characteristics within exposure classes were weakly influenced by storm-relative position and precipitation structure. Eyewall observations showed little difference in mean gust factors when compared with other regions. In convective precipitation, only peak gust factors were slightly larger than those found in stratiform conditions, with little differences in the mean. Gust factors decreased slightly with decreasing radial distance in rougher terrain exposures and did not respond to radar-observed changes in precipitation structure. In two limited comparisons, near-surface gusts did not exceed the magnitude of the wind maximum aloft detected through wind profiles that were derived from WSR-88D velocity?azimuth displays.