Miami/New Orleans Hit

[HurricaneBill]

Floydbuster:

I think the southern Gulf coast would be the Yucatan and Mexico.

Anita peaked as a Category 5 with sustained winds of 170 mph.

I count Texas as the northern gulf coast. So Allen is on the list.

Bret went from 140 mph to 115 mph in a short time, that's significant weakening.

Andrew went from 140 mph to 120 mph right before landfall. Maybe not falling apart, but significant weakening in a short period of time.

Opal dropped from 150 mph to 115 mph. She weakened just as quickly as she strengthened.

Hilda went from 150 mph to 125 mph prior to landfall.

Carmen is listed as making landfall as a Category 3 with winds of 115 mph. However, at landfall, the NE section of the eyewall had collapsed and Carmen probably quickly dropped below major status quickly thereafter.

I don't see how it is possible for Ethel to have gone from Category 1 to 5 and back to 1 in such a short time. Ethel would have still come in with a lower pressure. At landfall, the pressure was 981 mb. Ethel was probably a marginal Category 3 at most.

[Scorpion]

I highly doubt this is possible. It would need ideal conditions for the entire duration. Also, I doubt the waters can sustain a 900 MB hurricane. 920? Maybe. It would need to be very compact as well. This only happens when it develops much closer to land than typical Cape Verde storms.

[Huckster]

Andrew weakened 2 full categories over Florida.

Also, it weakened from 125KT to 100KT in the final 6-12 hours prior to its landfall along the Gulf Coast, which is actually quite typical of major hurricanes in the northern Gulf

To say that something is typical is to say that it is representative or characteristic of the group, family, setting, etc., of which it is a part. If significant weakening just before landfall is typical of major hurricanes landfalling in the northern Gulf Coast, then, it would seem, a majority of major hurricanes in that region would have to weaken significantly just before landfall.

In my opinion, there is only one practical way of looking at this. That one way is this, to look at every hurricane which made landfall in the northern Gulf of Mexico, which also was at major hurricane status 6-12 hours before landfall. By "northern Gulf Coast" or "northern Gulf of Mexico" let that be understood to be coast from Brownsville, Texas to Tampa, Florida.

I cannot give precise times of landfalls, so I will give the wind speed at what appears to be the first coordinate inland and the three coordinates preceding it. That would be inland, then six hours, then twelve hours, then eighteen hours before. Also, I am only using information which is included in the re-analysis, which only goes to 1910 so far. The reason is because there appear to be serious discrepancies in the data after that. For example, and this is the only purely Gulf storm for which I've seen the revised track data, the LA hurricane of 1926 was listed as a Cat. 2 at landfall, but it is now listed as a Cat. 3. I suspect there will be many other such changes, both up and down, but I don't think that will somehow completely overturn the nearly 60 years of evidence before it. Here we go:

H. #4, 8/23/1851 FL 90kt 100kt 100kt 100kt
H. #1, 8/26/1852 MS/AL 90kt 100kt 100kt 100kt
H. #5, 9/16/1855 LA/MS 100kt 110kt 110kt 100kt
H. #1, 8/10/1856 LA 110kt 130kt 130kt 120kt
H. #5, 8/31/1856 FL 90kt 90kt 100kt 100kt
H. #1, 8/11/1860 LA/MS 100kt 110kt 110kt 100kt
H. #3, 9/16/1875 TX 90kt 100kt 100kt 90kt
H. #4, 10/03/1877 FL 90kt 100kt 90kt 90kt
H. #4, 9/01/1879 LA 90kt 110kt 110kt 110kt
H. #2, 8/13/1880 TX 110kt 130kt 120kt 110kt
H. #2, 9/10/1882 FL 80kt 100kt 80kt 80kt
H. #5, 8/20/1886 TX 85kt 135kt 130kt 120kt
H. #10, 10/12/1886 LA 75kt 105kt 105kt 105kt
H. #10, 10/02/1893 LA 95kt 115kt 115kt 105kt
H. #5, 10/09/1894 FL 85kt 105kt 105kt 105kt
H. #4, 9/29/1896 FL 85kt 100kt 110kt 110kt
H. #1, 9/09/1900 TX 90kt 125kt 125kt 125kt
H. #6, 9/26/1906 MS/AL 65kt 95kt 95kt 100kt
H. #4, 7/21/1909 TX 90kt 100kt 90kt 80kt
H. #8, 9/21/1909 LA 105kt 105kt 105kt 105kt

I may have mistyped something, misread something, or just got it completely wrong, but I think most of these numbers are accurate. Now, I know these numbers are all estimates, and that means they might not be 100% right. However, I think there is a enough of a consensus to show that the majority of these storms did not drastically, amazingly, incredibly, or, miraculously weaken. That would mean that it is not typical for north Gulf major hurricanes to weaken 15 or 25 or even more knots right before landfall, at least based on this information.

Again, for storms after 1910, there are a lot of problems still. Nevertheless, let me give some guesses on some more recent storms.

2004, Ivan: how much did it weaken? I think that's probably the storm that really got all this intensity stuff going in the first place. Who knows, yet.
2002, Lili: if your faith is based on north Gulf storms falling apart right before landfall, then Lili would probably be either your patron saint or maybe your god. Even amongst weakening storms, Lili is not typical though. Few storms have weakened quite that quickly in the north Gulf.
1999, Bret: From 120kt to 100kt is rather dramatic. Dry air?
1995, Opal: 130kt to 100 is pretty signicant weakening. Shear and cooler water?
1992, Andrew: Andrew weakened a good bit, no doubt. Dry air I believe.
1985, Kate and Elena: Kate weakened quite a bit, but before jumping to conclusions, keep in mind that comparing a late November major hurricane to storms mostly from August to early October is not very reasonable. I don't know how much if any Elena weakened before hitting Mississippi, but I know it was not tremendous or anything. Certainly not Lili-esque.
1983, Alicia: No weakening I know of.
1980, Allen: Definite weakening, dry air I think, and slowing down.
1979, Frederic: A good example of a storm at least holding its own, no dramatic weakening.
1975, Eloise: No weakening.
1974, Carmen: Definite weakening. I have not found very much info about this storm, so I don't know what caused the weakening, but its track is kinda goofy looking. Looks like it slowed down as it neared the coast, so maybe dry air?
1970, Celia: No weakening.
1969, Camille: No weakening much if any.
1967, Beulah: Not sure, looks to have weakened and possibly have slowed.
1965, Betsy: Definitely doesn't seem to have been weakening at landfall. It took a very long time (relative to hurricanes) for it to start to fall apart after landfall.
1964, Hilda: Definite weakening, I think from 130kt to 105kt at landfall. That's pretty big. Storm definitely slowed down a lot right ahead of a coldfront, and I would bet this storm got sheared pretty badly near landfall and after.
1961, Carla: No weakening, as far as I can tell. If it was weakening, I cannot imagine how bad it would have been if it was strengthening.
1957, Audrey: Audrey was not weakening at all. In fact, it seems to have been strengthening and accelerating.

So that is 19 storms since 1950 that were majors right before landfall. Of those, about 8 hurricanes seem to have weakened significantly, (15kt or more is my guess). That's about 42% of storms. If we take out a couple of crazy storms, Audrey and Kate, that puts it at 7 out of 18 storms, or about 39%. Assuming this isn't all voodoo and snake oil, it would be hard to say that it is typical of north Gulf storms to weaken like Andrew did (25kt), much less like Lili. Of course, there are likely to be changes in all this data in years to come as it is reanalysed. This also makes me think that in that first batch of storms I mentioned, 1851-1910, some of those storms probably weakened more dramatically than is indicated, but most of them did not apparently try to commit suicide like a couple of more recent storms. My opinion is this, a not insignificant minority of the storms weakened significantly before landfall, with the majority roughly staying steady (slightly weakening/slightly strengthening).

I think the best way to look at this is to say it is typical of northern Gulf hurricanes to behave according to their environment. Storms which are slowing will tend to pull in dry air. Storms in the late season tend to be affected by shear and cooler waters or both. Allen, Andrew, Bret, and Carmen slowed and pulled in dry air most likely. Hilda, Kate and Opal were victims of fall weather patterns and cooler water. Lili was destroyed by Dynomat and Pat Robertson. The rest of the storms seem to have maintained themselves fairly well. I guess you could say it's not extremely uncommon for major Gulf storms to weaken a lot, but you'd still have to say most simply do not weaken all that much.

Comments and questions welcome.

[Derek Ortt]

my hypothesis is that the cat 4 and 5 storms weaken due to the cold shelf waters, but that the cat 2 and 3's intensify. I'd exclude Alicia, Frederic, and Celia from the sample because they moved into the northern Gulf at less than major hurricane intensity. The shelf waters may be able to support a cat 3 storm, refer to Emanuel's MPI papers for more information.

The storms I was naming were cat 4's and 5's when they moved into the northern Gulf and weakened upon landfall. It is possible that the NGOM can allow for a 2 to intensify into a 3, but causes a 4 to weaken back to a 3

[jimbo]

my hypothesis is that the cat 4 and 5 storms weaken due to the cold shelf waters, but that the cat 2 and 3's intensify. I'd exclude Alicia, Frederic, and Celia from the sample because they moved into the northern Gulf at less than major hurricane intensity. The shelf waters may be able to support a cat 3 storm, refer to Emanuel's MPI papers for more information.

The storms I was naming were cat 4's and 5's when they moved into the northern Gulf and weakened upon landfall. It is possible that the NGOM can allow for a 2 to intensify into a 3, but causes a 4 to weaken back to a 3

This is probably the most compelling statement of the lot to me (a gross amateur). The sustaining of a major for a short period time (like Camille) is evident, I'd love to see evidence supporting Derek's post to supoort or refute his staements.

Jim

[Derek Ortt]

I believe, that Camielle crossed an eddy near the coast, though from what I have heard, the landfall winds, while remaining at cat 5, did weaken somewhat at landfall

I'd have to look much more into this (would require an MWR paper or something, which, unfortunately, I dont have the time for right now -- other MWR papers), so I'd refer to Kerry Emanuel's work on MPI

[HurricaneBill]

I believe, that Camielle crossed an eddy near the coast, though from what I have heard, the landfall winds, while remaining at cat 5, did weaken somewhat at landfall

Wouldn't that be due to interaction with land?

[Anonymous]

Really.