Re: Remembering Katrina / Monitoring Ida - what led to Katrina's expanded windfield
Posted by
1969 on 8/28/2021, 4:34 pm
Found an interesting historical discussion of Katrina as to why it simultaneously weakened (to a category 3) by expanded its wind field.
In short, Katrina went through an ERC (Eye Wall Replacement Cycle). These sometimes occur in storms that exceed 127 mph.
See A key to Katrina's huge size and devastating impact
"Hurricane Katrina's eyewall replacement cycle over the northern Gulf and accompanying double eyewalls at landfall: A key to the storm's huge size and devastating impact over a three-state coastal region
Keith G. Blackwell, University of South Alabama, Mobile, AL; and A. Wimmers, C. Velden, P. J. Fitzpatrick, and B. Jelley
Hurricane Katrina made landfall on the Gulf Coast with the 3rd lowest central pressure (920 hPa) of any landfalling hurricane in United States history, but the pressure had been much lower before landfall. During the period of rapid strengthening over the central Gulf, Katrina contained one very intense eyewall. As the storm moved closer to the northern Gulf coast, the structure of Katrina changed dramatically when the storm began an eyewall replacement cycle. During this cycle, a developing outer eyewall began to encircle the inner eyewall and Katrina became a concentric two-eyewall storm. Katrina was one of five storms in 2005 to display a multiple eyewall configuration (Hawkins et al., 2006). The development of an outer eyewall greatly aided the dramatic increase in the size of Katrina as it approached the coast and allowed hurricane force winds to expand to a distance greater than 160 kilometers from the center. As Katrina went through the eyewall replacement cycle, the peak category 5 winds in the inner eyewall began to decrease as winds in the outer eyewall strengthened; during this structural transition, Katrina's winds officially slipped to a category 3 hurricane at landfall. Powell et al. (2007) show that even though the storm weakened to a category 3 at landfall, the great horizontal expansion of the wind field allowed Katrina's winds near landfall to maintain nearly the same kinetic energy of its earlier category 5 strength." |
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