Katrina's collapsing precipitation core at landfall

[MGC]

In my usual post hurricane damage analysis after Katrina, I observed that Hurricane Katrina's destructive winds along the Mississippi Coast were concentrated in eastern Hancock County and western Harrison County. I prefer to compare identical structures or vegetation (trees) to get a general estimate of wind damage. I travel the Mississippi Coast from Pascagoula to the MS/LA boarder several times. Without a doubt the wind damage from Long Beach to Waveland and inland was substantial with all decidious trees totally defoliated (similar to what I observed in Mobile Al after Fredrick) and plenty of snapped pine trees. The futher east one went the frequency of defoliation and snapped pine trees decreased with distance. I also observed two sets of street light at interchanges along I-10. One set was in eastern Hancock while the other was in Gulfport at the HWY-49 and I-10 interchange. The light poles in Gulfport remained standing while all light poles in Hancock were blown down. Thus, my conclusion that the winds in Hancock County were stronger. I didn't observe evidence of the second eyewall that came ashore near Biloxi. Perhaps the winds didn't mix to the surface as efficiently. I recently came apon an article on collapsing precipitation cores by Keith Blackwell of the University of South Alabama which helped shead light on the damage swath I observed. Convection in Katrina's eyewall was collapsing at landfall. Blackwell contends that: "evaporative cooling within dry air could significantly enhance the strength of convective downburst-like features." In all probility I observed damage from a massive downburst as convection collapsed just as Katrina made landfall. Blackwell studied many other hurricanes in his paper which include Ivan, Rita and Charley...MGC

http://ams.confex.com/ams/pdfpapers/138489.pdf

[brunota2003]

Basically, a large swath of straight line winds, right? That'd be a macroburst (>2.5 miles in diameter).