The Intensity of Wind Gust Underneath Areas of Deep Eyewall Convection in Hurricanes Katrina and Dennis at Landfall

Hurricanes Ivan (2004), Dennis (2005), Katrina (2005) and Rita (2005) produced extraordinary devastation along the Gulf Coast. This paper examines selected locations on both the immediate coastline and locations along inland bays and waterways, to determine not only the large-scale sustained wind fields and gusts associated with the primary storm vortex tangential flow, but also the localized gusts superimposed onto that mesoscale wind field by convective structures (feeder bands, tornadic MCVs, and elements of the eyewall). The study uses traditional land based observations (along with specially deployed portable stations set up in the path of the storms by Florida International University and the NOAA Hurricane Research Division) as well as interpolations generated by the HURRTRAK RMPRO 2005 software package, along with reconnaissance data (both flight level data and, in particular, GPS dropsondes) and WSR-88D Doppler velocity and reflectivity products.

This paper also uses data from SLOSH model products, as well as FEMA and US Army Corps of Engineer studies (including detailed post-storm analyses dividing the coastline into grid squares) to determine the magnitude and timing of the storm surge at each location. By combining wind and surge, a methodology is established to develop a meteorological timeline of events at each spot. This methodology can then be used to better establish estimations of how much of the damage to a particular property was caused by wind and/or surge, and, often more critically for insurance purposes, the timing of each form of damage.

Preliminary results show that winds at locations immediately adjacent to the Gulf of Mexico and large inland bodies of water (such as Escambia Bay, Florida and Biloxi Bay, Mississippi) show the effect of the much smaller frictional component of wind speeds over water in the lowest portions of the boundary layer. Very large gradients of wind speed across surprisingly short distances from these locations to those only a mile or less inland, suggest that much of the devastation in beachfront and bay front spots was caused by a combination of both wind and surge. The HURRTRAK software, and manual analyses of reconnaissance and other data sets at specific locations, can yield timelines of the magnitude of wind and surge (and their relative destructive potential) as the storm events unfolded.