Edit, 2am Sunday: Katrina has continued to rapidly intensify, as noted and forecast, and is now a powerful category 4 hurricane with winds of 145mph. No changes are needed to the forecast below, but this brings the risk to the New Orleans area to the forefront.

This evening, Katrina has completed an eyewall replacement cycle and is currently intensifying at a rapid pace, with its appearance on satellite imagery growing more impressive by the hour and pressures falling at a fairly substantial rate within the center of the storm, currently at 936mb. Normally, this would support a storm near category 4 intensity; however, the maximum flight level winds found within the storm so far this evening have been 114kt, equating to a weak category 3 at the surface. This has been the trend so far with the storm -- to have lower wind speeds than the pressures would normally support -- but whether or not this continues remains to be seen. Nevertheless, as the storm nears the diurnal convective max, moves further away from the eyewall replacement cycle, and hits the outer fringes of the Loop Current, the storm should continue to intensify through the overnight hours, potentially reaching beyond category 4 intensity by late morning Sunday. Another eyewall replacement cycle is likely before landfall, but trying to predict the timing of such an event is beyond our capabilities at this point in time.

First, the intensity forecast. Microwave data from around 8p ET suggest a very-well organized system with a developing eye (confirmed by recon) and a solid CDO feature. Buoys and satellite data indicate that sea surface temperatures ahead of the storm are slightly warmer than those it has just passed. As an aside, the intensity of the storm as it passed near the Dry Tortugas can be seen in the buoy data from that location earlier today, where the SST dropped from 85.5F to 82F over the course of a 24hr span. Nevertheless, SSTs ahead of the storm are around 90F, with sub-surface temperatures well into the mid 80s (as supported by a 89ft measurement of 88F at a reporting station about 100mi south of the projected landfall point). The hurricane heat potential maps highlight the loop current and its stretches of very warm and very deep waters just ahead of the storm. These strong storms normally mix (upwell) waters down to a depth of 60-70m below the surface; given highly favorable conditions at those levels, there is no reason to expect any substantial weakening of the storm (other factors aside, which appear to be favorable) as it approaches landfall -- the conditions near the Louisiana coast are quite different than those Dennis encountered near the Florida coastline last month. As a result, other than internal fluctuations (i.e. eyewall replacement cycles) over the course of the time before landfall, this storm should continue to intensify to that point, potentially reaching the upper threshold of category 4 intensity by landfall on Monday. It is not out of the question for this storm to reach category 5 intensity sometime between now and then; given inner-core fluctuations, however, I do not believe that the storm would landfall at quite that intensity. Nevertheless, winds of 145-150mph are possible with this storm as it makes landfall.

Thus begs the question, where is it going to make landfall? The ridge that had been keeping Katrina on a westward path has now moved to a location centered over South Carolina and is moving eastward. The upper-level trough expected to capture the storm is largely moving by too far to the north to capture it, but shortwave troughs passing through the southern Plains are providing enough of a weakness to likely capture the storm and send it towards the north through time. However, it is not a very strong weakness and will not capture the storm and accelerate it greatly to the north before landfall -- that acceleration will come after landfall as it gets captures in the midlatitude westerlies. (Similarly, the trough should not be large enough to impact the storm to a substantial degree in terms of shear or intensity.) Model guidance from both the 18z and 00z runs is tightly clustered and centered over New Orleans -- with the 00z models being weighted slightly east of the city, and the 18z models weighted slightly west of the city. There is good agreement on landfall occurring early in the afternoon on Monday, though conditions will begin to deteriorate through the evening hours on Sunday. Given the agreement in the model guidance and how the steering flow is currently playing out, I feel reasonably confident in projecting a landfall along the SE coast of Louisiana between 10a-4p CT on Monday afternoon. This would take the storm slightly east of New Orleans -- a dangerous surge and flooding scenario for the city, to say the least -- and inland near the mouth of the Pearl River. This track would also send high waves and surge well to the east of the storm, potentially flooding the coastline from Mississippi eastward to Escambia Bay, FL. Heavy rain will also be a concern with the storm, but given its intensity and track is not the greatest threat at this time. I cannot emphasize enough the danger to the entire northern Gulf coast with the forecast track of this storm -- whether mine or the NHC's, which are in large agreement. Note that a track over SE Louisiana would result in very little weakening of the storm by the time it approached New Orleans given the marshy conditions of the lowlands near the Gulf shore.

Anyone in a mandatory or voluntary evacuation zone should seriously consider leaving immediately for regions inland or far to the east or west. This storm is a large storm and will bring substantial impacts well to the west and east -- and to some degree north -- of the landfall point. There is still some uncertainty as to where this landfall point will be, meaning that those in the warning area (as of the 11p NHC advisory) should seriously consider leaving for higher ground and rushing to completion all precuations to protect life and property. To put it bluntly, get out now while you still have a chance. This has the potential to be a once-in-a-lifetime catastrophe at this point in time. Find a shelter, find relatives outside of the warning area, or simply find a hotel -- just do not hesitate to leave until it may be too late -- i.e. Sunday night.

The next update will come tomorrow night if conditions warrant. I will try to provide updates into Monday, but considering all that will be occuring around here, I may not be able to do so. Nevertheless, stay tuned here and to your local authorities for the latest information regarding very dangerous Hurricane Katrina.