Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 10:52 PM GMT on August 28, 2005
The 6:30pm EDT NOAA Hurricane Hunter mission found a central pressure of 904 mb, up from the 902 measured at 3:30pm. These pressures make Katrina the fourth strongest hurricane ever, and the strongest hurricane ever observed in the Gulf of Mexico, surpassing Camille. However, the winds of Katrina are 165 mph, far from Camille's 190 mph winds at landfall.
Although the pressure has stopped falling, there is no indication that Katrina is about to undergo weakening, like we saw yesterday during her eyewall replacement cycle. When that cycle started, the eye diameter was 9 nm, but the present eye diameter is 28 nm. Eyewall replacement cycles usually begin when the eye shrinks below 10 nm, and there are no indications that Katrina's eye is going to shrink.
The list of strongest hurricanes of all time now reads:
Hurricane Gilbert (888 mb, 1988)
The Great Labor Day Hurricane (892 mb, 1935)
Hurricane Allen (899 mb, 1980)
Hurricane Katrina (902 mb, 2005)
Hurricane Camille (905 mb, 1969)
Landfall location and intensity
Katrina has continued to expand in size, and now rivals Hurricane Gilbert and Hurricane Allen as the largest hurricanes in size. When hurricanes reach such enormous sizes, they tend to create their own upper-air environment, making them highly resistant to external wind shear. The global computer models are not really hinting at any wind shear that might affect Katrina before landfall, and the only thing that might weaken her is an eyewall replacement cycle. Even if one of these happens in the next 12 hours, the weakest Katrina is likely to get before landfall is a Category 4 hurricane with 145 mph winds. Katrina is so huge and powerful that she will still do incredible damage even at this level. The track forecast has not changed significantly, and the area from New Orleans to the Mississippi-Louisiana border is going to get a catastrophic blow. I put the odds of New Orleans getting its levees breached and the city submerged at about 70%. This scenario, which has been discussed extensively in literature I have read, could result in a death toll in the thousands, since many people will be unable or unwilling to get out of the city. I recommend that if you are trapped in New Orleans tomorrow, that you wear a life jacket and a helmet if you have them. High rise buildings may offer good refuge, but Katrina has the potential to knock down a high-rise building. A 25 foot storm surge and 30 - 40 foot high battering waves on top of that may be able to bring down a steel-reinforced high rise building. I don't believe a high rise building taller than six stories has ever been brought down by a hurricane, so this may not happen Monday, either. We are definitely in unknown waters with Katrina.
I have focused on New Orleans in much of my discussions about this storm, but Katrina will do tens of billions in damage all along the coast of Louisiana, Mississippi, Alabama, and Florida. Mobile Bay could well see a 10-foot storm surge. And inland areas will take heavy damage as well; Katrina will still be a hurricane 180 miles inland, and cause widespread flooding throughout the Tennessee Valley.
My thoughts and prayers go out to all of you in Katrina's way, and I urge all readers of this blog to do the same.
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