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Katrina--costliest hurricane ever?

By: Dr. Jeff Masters, 11:49 AM GMT on August 27, 2005

The Hurricane Hunters measured a cental pressure of 941 mb at 7:07am EDT, up 2mb from the 940 mb pressure recorded at 5:32am. The maximum winds recorded at flight level (10,000 feet) were just 106 knots, which meaning that Katrina is still a Category 3 storm, even though the pressure implies she could be a Category 4. The reason for this is that a significant increase in the areal extent of the storm has occurred in the past six hours, so Katrina needs to spin up a much larger area of winds, which will take time. It is likely that by this afternoon, the winds will "catch up" to the pressure, and Katrina will go from being a small, weak Category 3 storm to a medium-sized strong Category 3 hurricane. Recon noted that the eye diameter has shrunk to 9 nm, which is about as small as the eye can get before an eyewall replacement cycle begins. If this is the case, Katrina will probably not attain Category 4 status until eyewall replacement cycle ends and a new round of intensification begins, which would likely not happen until Sunday. A few of the NHC intensification models from last night suggested the possibility that Katrina could reach Category 5, which is not unrealistic, given the warm waters and light wind shear over the storm. Katrina still has a way to go to reach Category 5; the convection and outflow are still looking restricted on the north side of the hurricane, and this area will have to "catch up" before we can talk about Category 4 or Category 5.

Figure 1. Hurricane Katrina in the Gulf of Mexico at 4:20 PM GMT on August 27, 2005.

The favorable conditions for Katrina are expected to last up until landfall, when some increase in shear may occur. But as usual, intensification forecasts are highly unreliable, and we don't really know how strong Katrina will be at landfall. The track forecast is also problematic, until Katrina makes its northward turn. She is apparently beginning to do so now, as the track has been wobbling more westward that west-southwest the past few hours.

Emergency management officials in New Orleans are no doubt waiting to see where Katrina makes her turn before ordering evacuations. However, if I lived in the city, I would evacuate NOW! The risks are too great from this storm, and a weekend away from the city would be nice anyway, right? GO! New Orleans needs a full 72 hours to evacuate, and landfall is already less than 72 hours away, so I would get out now and beat the rush. If an evacuation is ordered, not everyone who wants to get out may be able to do so.

Insurers estimate that Katrina already did about $1 to $4 billion in damage (total damage is roughly double insured damage). This is a shocking number for a Category 1 hurricane, and bodes ill for the residents of New Orleans and the U.S. insurance industry if Katrina makes a direct hit on New Orleans as a Category 4 storm, which would likely cost $100 billion. But, New Orleans' amazing run of luck could well continue at the expense of Mississippi or Alabama or Florida. Like Camille in 1969, Katrina may come ashore far enough east of New Orleans to largely spare it.

Dr. Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.