Windspeed wrote:I adamantly disagree that the maximum potential for intensity at landfall over the northern Gulf of Mexico is upper category three or winds between 125-130mph sustained. I do not want to call Derek out, but I will gladly debate him on this if he so chooses. I have seen Derek make this claim over the past few years and I consider his idea has some merit because often hurricanes do weaken on approach with the coastline along the northern Gulf of Mexico. However, each hurricane had a different circumstance with both its atmospheric environment and its source with oceanic heat potential. My main argument is that though the occurrence of landfalling category four and five hurricanes may be infrequent along the northern Gulf coastline, the consistency of category three landfalling storms should not be the basis for setting that region's maximum potential for intensity at category three. I want to show there is a range between tropical cyclone heat potential (TCHP) of the shallow shelf versus rate of motion of the core of an intense hurricane. Continental airmass is also highly influential on the intensity of landfalling hurricanes on the northern Gulf Coast. Category 4 and 5 landfalls are infrequent by their nature, but there is a window of opportunity along the northern Gulf Coast that will support category 5 landfalls. I believe such window is very dependent on three factors: 1) The shape and location of the Loop Current and any subsequent warm core ring (WRC) or "eddy;" 2) The temperature at the immediate surface (SST) right at the coastline and on the shallow shelf; and 3) the position of continental airmass and its moisture content with respect to the core of the hurricane before landfall. There is such a scenario I will try to quickly show that may have occurred during an intense system like Hurricane Camille and why I believe it will occur again.
The main focus of this post is heavily reliant on the constant evolution of the Gulf Loop and subsequent eddies or warm core rings that it sheds over the course of a six to eleven month cycle. Most of you should be familiar enough with how the main Gulf Loop current works so that I will not have to explain it in detail. You can go
here,
here and
here to read up on how this current and subsequent eddies influenced the rapid intensification of three closely studied systems, Hurricane's Katrina, Rita and Opal.
If your connection is high speed, you should also watch the following animation of how the Loop Current generates warm core rings and eddies
here.
Now I am quite certain that no one here, including Derek, denies the important relationship between the Gulf Loop and rapid intensification of systems that traverse that region of the GOM. However, I wish to point out that the location of the Loop Current before it sheds a new warm core ring (WCR) ring may dramatically increase the chances of a Cat 4-5 storm intensifying all the way up to landfall on the northern Gulf Coast. Keep in mind the Gulf Loop is ever changing and can often times exclude the region just south of the shallow shelf, or it can stretch from the straits all the way to the shelf wall varying in range and shape. I also feel that forward motion of the core of the cyclone is vital to this process once the storm moves off the most northern extension of the current and onto the shallow shelf right before landfall. In other words, I am trying to show that timing is everything...
Please review the following images:
This is how the current Gulf Loop and it's subsequent eddy look at present:
http://www7320.nrlssc.navy.mil/global_nlom32/navo/IASSP1.gifThe TCHP map reflects the location of these features:
http://www.aoml.noaa.gov/phod/dataphod1/work/HHP/NEW/2007238go.jpgAs you can see, there is a WCR that has been shed from the Gulf Loop. This WCR eddy was shed over the past two months and is ripe for supporting any major hurricane that would potentially bare down on the Louisiana coastline. This WCR has a 26ºC isotherm well down around 100m with very high TCHP above. It is also important to note that the shallow shelf just south of Louisiana is over 30ºC.
The temps right at the surface and notice the 30+Cº currently on the shallow shelf:
http://www.aoml.noaa.gov/phod/dataphod1/work/HHP/NEW/2007238gosst.pngGranted, this is shallow due to the presence of the shelf. This is also a contributing factor to why the SSTs are so high on the shallow shelf in July/August as the influences of daytime heat/land breeze from over land is the warmest of the year with direct sunlight insolation at its highest lagging from June; furthermore, an absence of cold fronts to cool the shallow shelf during those months. If an intense hurricane moved at a decent rate of speed over this region with favorable atmospheric support, I think the storm would be able to maintain Cat 4 to 5 intensity, such as Camille did in 1969. I also believe that Camille did not have time to be sufficiently weakened from the influences of a continental drier continental airmass, or, the core of the storm was embedded within a sufficiently moist environment to avoid erosion of the core. A slower moving or larger storm might well enough have upwelled the cooler waters of the shallow shelf, or entrained drier continental airmass quick enough to weaken on that same shallow shelf. I feel speed of motion of the core of a hurricane is much more important to maintain higher intensities over a region of high SST temps versus lower TCHP.
I suspect the shape of the Gulf Loop right before generation of new WCR eddy might open up the door in conjunction with 30º+C SSTs on the shallow shelf, providing an avenue for which a hurricane at Cat 4-5 intensity could maintain through landfall. Consider the following shape of the Gulf Loop such as this:
Notice how far north the Loop Current is just as it is about the shed a new eddy. It is literally running right up to the shallow shelf just south of the Panhandle and Alabama. Imagine if you will, Dennis or Ivan having the luxury of the Loop Current with this shape and current SSTs right on the shallow shelf running at 30ºC. Yes, the maximum potential would be far greater than a 130mph hurricane. Factor in forward speed of a faster moving hurricane, I think you have the ingredients for a landfalling category four or five storm. Of course, there's more than oceanic heat. You also need favorable atmospheric conditions.
So what was really occurring during Camille?
Well unfortunately during Camille we did not have the remote sensing techniques to samples of the oceanic and atmospheric environment that compare to the technology we have available today. However, I can play out a plausible scenario....
Keep in mind this is purely speculation on my part, if only influenced in small part by the recon and satellite data available at the time. Camille moves away from the western tip of Cuba and enter the region of the Gulf Loop. The core is relatively small during initial rapid intensification phase as it begins move over the high TCHP of the Gulf Loop.
http://en.wikipedia.org/wiki/Image:Hurricane_camille.jpgCamille rapidly bombs with a very intense pinhole eye somewhat similar to Hurricane Charlie's rapid intensification; however, being over such high heat potential, the outer banding features are likewise able to consolidate and intensify rapidly around the core and the CDO.
http://en.wikipedia.org/wiki/Image:Hurricane_Camille_16_aug_1969_2340Z.jpgThe overall size of Camille expands though the core remains very intense as the storm approaches the southeastern Louisiana coastal shelf. The Gulf Loop may have assisted in keeping Camille intense right up to the shelf as it may have shed or been in the process of shedding a WCR eddy.
http://en.wikipedia.org/wiki/Image:Hurricane_Camille_17_aug_1969_1957Z.jpgAlso, being middle-to-late August, the shallow coastal shelf may have been over 30ºC in SST at the immediate surface. Camille's outer banding features consolidate a concentric eyewall and the core weakens somewhat between 24 and 12 hours prior to landfall; however, the inner core remains relatively small and stabilized or begins to re-intensify upon landfall. The core is also embedded in a sufficiently moist enough environment to ward off intrusion of continental airmass, Camille's smaller circulation may have helped itself along in this process. Also keep in mind, Camille was steaming NNW well inland into the upper Mississippi coastal plain before it slowed and turned into the westerlies.
http://en.wikipedia.org/wiki/Image:Camille_1969_track.pngGranted it was moving into a weakness, but it may not have had the effects of mid-level intrusion that can occur with a digging shortwave trough. Camille crosses the shallow shelf with a shallow 26º isotherm but at a sufficient rate of speed to avoid its own upwelling and makes landfall with sustained winds above 155mph. Granted, maybe it was not the absurd 190mph sustained winds that were probably more indicative of wind gusts; but I am confident Camille restrengthened or maintained such status prior to landfall to be at the category five classification. I am also confident we will see another category five hurricane make landfall on the Louisiana to Panhandle coastline again.
