Hurricane Katrina Update 280400 CDT
At 4 AM CDT, the center of extremely dangerous Hurricane Katrina was at 25.4 North 87.4 West, 275 miles south-southeast of the mouth of the Mississippi River and moving to the west-northwest at 10 mph with a turn to the northwest. Winds are up to 145 mph and minimum central pressure is 935 millibars (27.61")
Hurricane Katrina Advisory Number 21
Katrina continues to both strengthen and grow in size. While the official forecast does not call for a further increase in size, it is possible. The Statisical Hurricane Intensity Prediction Scheme does call for Katrina to make category five before landfall, however the official forecast goes just short of that (155 mph) due to the unpredictable nature of structural changes of the eye that would weaken Katrina temporarily. While the specifics are unknown exactly, it is clear that Katrina will be a very dangerous hurricane at landfall.
Katrina is moving along as forecast. Models are in tight agreement and their consensus has barely shifted from their past run. As such, the track forecast is merely an update of the previous one (i.e. the only thing that changed was the initial position).
Hurricane Katrina Discussion Number 21
Official forecast track with watches and warnings
Here is the model guidance, which is nearly unaminous in putting New Orleans in the bullseye. The only deviator being the North American Model (NAM, labeled ETA1 in this graphic); it is a hemispheric model that does not exhibit much skill in tropical cyclone forecasting.
So, those who went to bed thinking that the storm would either not strengthen or would deviate from forecast 'like it always does' are facing reality this morning. An extremely dangerous hurricane is taking the worst possible path.
If you are in New Orleans, you should leave now. Going west is the preferable option, with north being a viable one as well. Note that it doesn't have to be particularly far west as the worst effects of the storm are on the eastern side of it. People in coastal areas east of the center line should head inland by proceeding north.
In New Orleans, traffic is liable to be bad enough to justify leaving now, rather than spending time to secure property. In any event conditions will start to rapidly detoriate tonight, so the absolute latest one could plausibly hit the road in a safe manner would be early afternoon.
One note on the possibility of Katrina weakening due to an eyewall replacement cycle. Weakening is a relative term. If we were talking about a category three storm, then weakening from an ERC does reduce the hurricane's winds to those that are not particularly damaging. However, when we are talking about a category five or a strong category four as we are with Katrina, an ERC is only going to knock her down to category three. Category threes are still dangerous and destructive storms. It would not create catostrophic damage in New Orleans, but damage would still be major.
Looking at the Tropical Cyclone Heat Potential chart, I notice that Katrina is yet made her way across the hot spot yet.
Cutting this short and here's why:
URNT12 KNHC 281120
VORTEX DATA MESSAGE
B. 25 deg 39 min N 087 deg 32 min W
C. 700 mb 2310 m
D. NA kt
E. deg nm
F. 141 deg 153 kt
G. 046 deg 018 nm
H. 910 mb
I. 10 C/ 3056 m
J. 25 C/ 3057 m
K. 10 C/ . CLOSED WALL
N. 12345/ 7
O. 1 / 1 nm
P. AF302 1712A KATRINA OB 10MAX FL WIND 153 KT NE QUAD 10:58:50 Z
That is a report from the recon plane. Pressure has plummeted. Katrina has gone category five.