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NEW DATA SUGGESTS KATRINA WAS MUCH STRONGER AT LANDFALL
By: ncforecaster , 6:55 AM GMT on August 30, 2007
I want to begin this particular blog entry by personally thanking each and everyone one of you who has taken the time to read and/or post in my previous couple of blogs (many of which have been long time friends from this wonderful community). I have chosen to commemorate the two year anniversary of hurricane Katrina's catastrophic landfall along the northern U.S. Gulf Coast by discussing the significance of hurricane Katrina's true landfalling intensity when it barrelled ashore. To be most specific, I want to share a most fascinating and interesting independent reanalysis by Captain Ronald E. Hughes, USN (Retired). It is an absolute must read for anyone interested in knowing just how strong hurricane Katrina may truly have been when she struck the Northern Gulf Coast. This reanalysis makes a very strong case that the NHC inadvertinly misinterpreted the available data which survived the storm. In doing so, they unjustifiably reclassified hurricane Katrina as only a 120-125 mph category three in their subsequent post storm reanalysis. As many of you may recall, I have consistently felt the NHC's post operational downgrade and their subjective rationale did not adequately explain nor correlate with the measurable components regarding this powerful storm. They had to rewrite the meteorological record in trying to justify how the third most intense storm in U.S. recorded history (920 mb) with the largest recorded storm surge to ever impact the U.S. shoreline (measured at 28 feet along the Mississippi coastline) was merely a 120-125 mph category three at the two respective Gulf Coast landfalls. It is also important to note that the barometric pressure had risen to a still remarkably intense 927 mb as Katrina's eye officially came ashore near the La./Mississippi border bringing with it the immense and historic 28 foot storm surge.
At face value, the two respective barometric pressure readings at landfall would typically equate to a high end category four storm (the La. reading being a borderline category pressure). As far as the recorded storm surge is concerned, it is in a category all by itself. Only the second most intense landfalling hurricane to ravage U.S. shores (category five Camille) has produced a storm surge within comparable range of hurricane Katrina's. It is also important to note that category five storm surge is characterized as being greater than 18 feet (a full 10 feet below the astonishing value register with Katrina). Although, this data would otherwise imply that Katrina could have been declared a category five at landfall, there are other important meterological intangibles that conspired to strip hurricane Katrina of that classification (where it stood operationally only 5 hours prior to La. landfall) in complete objectiveness. As we know, Katrina was gradually weakening during the last 14 hours prior to making landfall (barometric pressure rose from 902-920 mb) along the extreme La. shoreline. This weakening began shortly after huricane Katrina had obtained her peaked intensity while registering a barometric pressure of 902 mb accompanied by maximum sustained winds of 175 mph as she began to undergo a significant structural change known as an eyewall replacement cycle.
In simplest terms, it is the process where an outer eyewall develops from powerful convective rainbands merging together around the single smaller (i.e. inner eyewall) eyewall that had previously existed before the process began. As a result, the inner eyewall begins to weaken as it's energy is being zapped by the newly formed and intensifying outer eyewall. Once this process reaches completion, the inner eyewall will have completely dissipated, and the storm will once more retain a single eyewall. The major difference being that this newly formed eyewall is much larger than the one that preceded it. Consequently, the larger eye coincides with a larger pressure gradient (difference in wind speeds over a given distance) whereby the storms top winds will decrease. Depending upon the other atmospheric parameters in play (i.e. atmospheric conditions such as vertical wind shear, water temperatures, proximity to land, dry air infiltration, etc.), the storm can and often times reintensifies. This occurs as the new single eyewall shrinks in size, which enhances the pressure gradient whereby the top winds increase once again (given the right conditions, to an intensity greater than before). Moreover, these EWRC most often coincide with an overall broadening of the wind field and overall size of the storm itself. In the case with hurricane Katrina, she began an EWRC roughly 14 hours prior to La. landfall that saw her barometric rise to 920 mb and the top sustained winds of 145 mph operationally. In addition, she expanded her wind field to where hurricane force winds extended outwards 125 miles from the center of the eye from the 105 miles prior to the onset of the EWRC. This weakening trend was also aided by the intrusion of dry air as it drew closer to land as well as slightly cooler water temperatures nearer the coastline. Furthermore, an increase in wind shear and the intrusion of dry air be the main culprits that caused the observed erosion of the inner eyewall on the SW side as it was coming ashore. Given all of the aforementioned evidence, the official operational landfalling intensity of 140-145 mph (strong category four) seems most logical.
In short, this very large category four hurricane that only 14 hours earlier retained 175 mph category five intensity, would better explain the record 28 foot storm surge that battered the Mississippi coastline, as well as how she was able to deliver such extensive wind damage some 150 miles inland. These inland effects consisted of the equivalent of F2 type tornado damage more than 110 miles from the shoreline. This wind damage was the result of measured wind gusts exceeding 120 mph in Laurel, Mississippi (located 110 miles from the shoreline). Naturally, the wind damage became increasingly more extensive as one got closer to the coast where Hattiesburg had wind gusts estimated at 125-130 mph (70 miles inland), and Poplarville (50 miles inland) recorded a peak gust of 135 mph (before the anemometer was destroyed by the powerful winds). Since most anemometers were either disabled or destroyed before the arrival of the peak conditions associated with the storm, the NHC had very little and very incomplete measurable wind data to assist them with determining the highest maximum wind speeds that were truly experienced along the coastline for the two respective Gulf Coast landfalls. As a result, much of it was left to conjecture and subjectivity, in order to best theorize how strong the winds might actually have been.
As noted earlier, the independent reanalysis alluded to earlier (with link provided) discusses how the NHC apparently misinterpreted the data that existed. Most notably, they apparently didn't recognize the presence and true intensity of the outer eyewall which had intensified, but not weakened the inner eyewall as first suggested by the NHC report. This was the result of Katrina's EWRC being halted prematurely by its interaction with land. Thus, Katrina was able to retain more intensity (i.e. not as much weakening as suggested in the NHC post storm reanalysis) when she made her catastrophic and historic landfall. The author of this report argues that hurricane Katrina's category five wind gusts destroyed many structures that were virtually left unscathed by Katrina's storm surge. Likewise, He provides documented evidence to support this assertion that suggests Katrina's powerful winds from the outer eyewall destroyed many structures well before Katrina's massive storm surge reach the shoreline. For countless individuals and families still homeless (or living in Fema trailers) and the thousands who have had their insurance company refuse to fulfill their commitments to help them rebuild (declaring their homes were destroyed by flood damage from the storm surge) by referencing the NHC revised 120-125 mph category three landfalling intensity makes a thorough reanalysis of the legitimacy of the NHC post operational downgrade most significant. Even more startling is the fact that many insurance companies are winning lawsuits to deny coverage on the basis that the NHC and its sister branches have officially suggested that only category two sustained winds impacted the hardest hit areas.
In conclusion, I firmly believe the meterological data, eyewitness accounts, and the immense observable catastrophic damage left in Katrina's wake all support the operational category four 140-145 mph landfalling intensity (for the Buras, La. Landfall), as opposed to the current revised post operational 120-125 moderate category three. In regards to the second Gulf Coast landfall near the La./Mississippi border, I would suggest that hurricane Katrina still maintained the lower end of category four intensity (135 mph), which would support the idea that 155 mph gusts (as has been estimated by various sources) destroyed beachfront homes, as expressed in the independent reanalysis. It took the NHC ten years to upgrade hurricane Andrew to a 165 mph category five at landfall in southeast Fl. from the operational 145 mph category four. In this case, one can only hope they will be more expedient in adjusting the true intensity of what appears to have been a powerful category four landfall of immense proportions. Most relevant is the fact that thousands of victims of this devastating storm are continuing to be adversely impacted more than two full years after their homes were apparently destroyed by her powerful winds, rather than water (as their insurance companies claim).
Hurricane video (estimated 155 mph gusts)
Credits go to Dave Lewison (Face the Wind)
Forrest County, MS. Inland Damage
Credits go to the Jackson, MS. NWS
Note: This is where I filmed Katrina in South Hattiesburg, Mississippi (65 miles inland)
Katrina Wind Speed Map
Credits go to "Forest One"
Report on "wind gusts underneath areas of deep eyewall convection in hurricanes katrina and Dennis at landfall"
Credit goes to Richard G. Henning (46th weather squadron, Eglin AFB, Fl.)
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