The Hurricane Hunters measured a central pressure of 949 mb at 11:14am EDT, up from the cental pressure of 941 mb measured at 7:07am EDT. Concentric eyewalls with diameters of 13 and 40 nm were reported, satellite images show that the eye has filled in with clouds and the cloud top temperatures have warmed. These observations indicate that an eyewall replacement cycle has begun. This was expected, since the 7:07am Hurricane Huneter report indicated that the eye diameter had shrunk to 9 nm, about the smallest diameter one gets before an eyewall replacement cycle begins.
The maximum winds may fall below 115 mph while Katrina undergoes this eyewall replacement cycle, as the inner eyewall collapses and a new outer eyewall forms. This would make Katrina a strong Category 2 storm, and indeed the maximum winds seen so far by the Hurricane Hunters were only 87 knots (100 mph) at 10,000 feet. This is a temporary affliction, since Katrina is in nearly ideal conditions for strengthening, and is expected to reach Category 4 status by Sunday. The convection and outflow are starting to look better on the north side of the hurricane, and Katrina should have a more symmetrical shape typical of Category 4 hurricanes by Sunday. As seen in the cumulative wind image below, Katrina has increased markedly in size the past 12 hours, and will deliver a widespread damaging blow wherever she comes ashore.
The favorable intensification conditions for Katrina are expected to last up until landfall, when some increase in shear may occur. Intensification forecasts are highly unreliable, though, and it would be no surprise if Katrina were a Category 2, 3, or 4 landfall. The track forecast is getting more believable, as Katrina's westerly motion shows that it has begun it recurvature, pretty much where NHC and the models were predicting. A landfall between New Orleans and Pensacola is on track for Monday morning or afternoon. I expect a Category 3 storm at landfall.
I'd hate to be an Emergency Management official in New Orleans right now. Katrina is pretty much following the NHC forecast, and appears likely to pass VERY close to New Orleans. I'm surprised they haven't ordered an evacuation of the city yet. While the odds of a catastrophic hit that would completely flood the city of New Orleans are probably 10%, that is way too high in my opinion to justify leaving the people in the city. If I lived in the city, I would evacuate NOW! There is a very good reason that the Coroner's office in New Orleans keeps 10,000 body bags on hand. 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. Get out now and beat the rush. You're not going to have to go to work or school on Monday anyway. If an evacuation is ordered, not everyone who wants to get out may be able to do so--particularly the 60,000 poor people with no cars.
Dr. Jeff Masters