Hurricanes slow as they approach Gulf Coast

[fwbbreeze]

http://www.pnj.com/article/20110531/NEWS01/105310314/Hurricanes-slow-they-approach-Gulf-Coast-researchers-find?odyssey=tab|topnews|text|FRONTPAGE

"Doyle Rice

USA Today
Cool waters just below the surface of the Gulf of Mexico cause the strongest hurricanes to almost always lose intensity before they hit that part of the U.S. coast, according to new research. The findings could help scientists more accurately forecast the storms during this year's hurricane season, which begins Wednesday."

[srainhoutx]

http://www.pnj.com/article/20110531/NEWS01/105310314/Hurricanes-slow-they-approach-Gulf-Coast-researchers-find?odyssey=tab|topnews|text|FRONTPAGE

"Doyle Rice

USA Today
Cool waters just below the surface of the Gulf of Mexico cause the strongest hurricanes to almost always lose intensity before they hit that part of the U.S. coast, according to new research. The findings could help scientists more accurately forecast the storms during this year's hurricane season, which begins Wednesday."

Folks that experienced Alicia 1983 would beg to differ with this.

[wxman57]

I think the other factor mentioned in the article is far more significant than the brief period over slightly cooler water:

Researchers also found another factor that causes big hurricanes to weaken: strong upper-level winds that storms encounter while approaching the Gulf Coast.

I'd argue that increasing wind shear accounts for the bulk of the weakening. Wind shear certainly weakened Rita and Lili, and likely Katrina and Ivan. Katrina was also beginning an eyewall replacement cycle as it approached SE LA/MS, which would naturally lead to weakening.

Wind shear can tear a hurricane apart within hours, while slightly lower oceanic heat content might only very slowly impact intensity.

And what's with the title of the article? There's nothing in the article about hurricanes slowing down prior to making landfall.

[RL3AO]

Naturally if a storm is heading north to hit the gulf coast, its now feeling large effects of the sub tropical steering currents.

[psyclone]

apparently slow=weaken for the author. i thought slow meant forward speed and i think to us it does. one factor not mentioned that probably trumps importance of sea surface temp is a greater probability of a cyclone to ingest dry continental air as it approaches the coast. that + hostile upper level winds probably knocks the biggies down. i was surprised to learn that weaker canes tend to strengthen.

[LSU2001]

I don't like the potential problems that could be created by this research. If forecasters actually start taking this into account then I could see major problems ahead. If forecasters start making public announcements that a cat 5 monster in the central gulf heading for the northern gulf will probably weaken, it would be very hard to get people to evacuate as necessary. If you had a Katrina situation developing and people thought the storm was going to weaken then people who need to leave would either wait until the last possible minute to evac or may even decide to ride the storm out. We have enough problems in South Louisiana getting people to leave now! I can see the scientific merit in this research but if used for the public forecasts I can see a far greater loss of life from a monster cane that does not weaken as forecast or that does not weaken enough. Katrina may have weakend in wind speed but still carried a monster surge ashore. This focus on wind speed will continue to kill people and is in my humble opinion very irresponsible.
Sorry for the rant,
Tim

[MGC]

Tell that to Hurricane Betsy, Fredrick and Camille. We here along the north gulf coast have been very luck in past years where shear and dry air have caused some drastic changes in the structure of the hurricane. I have talked to several people who think that it is natural for a hurricane to weaken as it approachs the coast. One day a system will RI like Charley did and surprise a bunch of people....MGC

[Ivanhater]

It doesn't matter much if big hurricanes weaken as they approach the Northern Gulf coast. Katrina and Ivan both produced Cat 3 winds along the immediate coast, but the majority of damage came from the massive surge and waves. Those factors don't weaken as the big canes head toward the northern Gulf coast.

[MGC]

Would you have prefered if Ivan had retained its Cat-5 winds and not its expanded wind field? It is a double edged sword...trade a cat or two of winds for a expanded wind field and higher surge....pick your poison. But, the public just looks at the SS scale and say Katrina and Ivan were only Cat-3 while Charley was a 4 and conclude that Charley was a more intense hurricane (which it was in terms of its tiny wind field).....MGC

[psyclone]

if you think about it, it does make sense that most (not all) strong hurricanes would tend to weaken as they approach land. after all, if the storm is symetrical, half of the circulation is already over land at the time of landfall. it only makes sense that most storms would begin to degrade under such circumstances. that said, I'm not taking solace in a storm degrading from a high baseline. if a cat 4 coming at you weakens to a 3, you're still going to have a very bad day. and that says nothing of the exceptions that don't weaken.

[Ivanhater]

Would you have prefered if Ivan had retained its Cat-5 winds and not its expanded wind field? It is a double edged sword...trade a cat or two of winds for a expanded wind field and higher surge....pick your poison. But, the public just looks at the SS scale and say Katrina and Ivan were only Cat-3 while Charley was a 4 and conclude that Charley was a more intense hurricane (which it was in terms of its tiny wind field).....MGC

I agree MGC. By the time Katrina and Ivan weakened as they approached the NGC, it was too late. The massive surge and waves already built up. As you said, the news coming out said they were weakening; however, the massive surge and waves were still on their destructive path.

[Cyclenall]

It annoys me too when authors and news reports use the word slow for weakening. What would forward movement of the tropical cyclone be called then?

[StormClouds63]

It's always an interesting discussion as to whether major hurricanes weaken as they approach landfall on the Gulf coast. I'd encourage everyone to read the section on Hurricane Audrey in the following publication, Storm Tides in Twelve Tropical Cyclones:

http://www.aoml.noaa.gov/hrd/Landsea/12Tides.pdf

Audrey has been re-analyzed, and it turns out the winds were considerably lower than originally thought. However, the radius of maximum winds was rather large, and caused a tremendous storm surge over SE Texas and SW Louisiana. Pressures were in the range consistent with a category 3 storm.

I'll really be interested to see what the re-analysis turns out to be on Camille ... as of now, the only category 5 to make landfall on the northern Gulf coast. I do think the "official" wind speeds of 190 mph may be too high. In several storms of the period, wind speeds tended to be overestimated. I think sustained winds in the 150-170 range are more likely. Unlike some, I think Camille will remain a 5 even after NHC re-analysis is completed.

We all know Katrina, Rita, Opal, and Ivan weakened prior to landfall. However, Alicia, Celia, and Eloise strengthened prior to landfall. If I'm not mistaken, the eye of Ike was consolidating as the storm approached landfall. Carla may have weakened from a 5 to a 4, but like Katrina its surge and winds covered an incredibly large area.

Size does matter w/tropical systems. Also, the SS scale may be outdated and need revision. Ike was a 2, but tell that to anyone in SE Texas or SW/S Central Louisiana. A so-called "weakening" storm can be just as deadly, especially if these are large systems where the effects of surge and winds are spread out over large areas as it approaches the coast.

[Ptarmigan]

Tell that to Hurricane Betsy, Fredrick and Camille. We here along the north gulf coast have been very luck in past years where shear and dry air have caused some drastic changes in the structure of the hurricane. I have talked to several people who think that it is natural for a hurricane to weaken as it approachs the coast. One day a system will RI like Charley did and surprise a bunch of people....MGC

Or Ike. Ike was a Category 2 when it hit Texas. A large non-major hurricane is WAY MORE dangerous than a small Category 5 hurricane. The massive storm surge leveled Bolivar Peninsula.

[Ptarmigan]

It's always an interesting discussion as to whether major hurricanes weaken as they approach landfall on the Gulf coast. I'd encourage everyone to read the section on Hurricane Audrey in the following publication, Storm Tides in Twelve Tropical Cyclones:

http://www.aoml.noaa.gov/hrd/Landsea/12Tides.pdf

Audrey has been re-analyzed, and it turns out the winds were considerably lower than originally thought. However, the radius of maximum winds was rather large, and caused a tremendous storm surge over SE Texas and SW Louisiana. Pressures were in the range consistent with a category 3 storm.

I'll really be interested to see what the re-analysis turns out to be on Camille ... as of now, the only category 5 to make landfall on the northern Gulf coast. I do think the "official" wind speeds of 190 mph may be too high. In several storms of the period, wind speeds tended to be overestimated. I think sustained winds in the 150-170 range are more likely. Unlike some, I think Camille will remain a 5 even after NHC re-analysis is completed.

We all know Katrina, Rita, Opal, and Ivan weakened prior to landfall. However, Alicia, Celia, and Eloise strengthened prior to landfall. If I'm not mistaken, the eye of Ike was consolidating as the storm approached landfall. Carla may have weakened from a 5 to a 4, but like Katrina its surge and winds covered an incredibly large area.

Size does matter w/tropical systems. Also, the SS scale may be outdated and need revision. Ike was a 2, but tell that to anyone in SE Texas or SW/S Central Louisiana. A so-called "weakening" storm can be just as deadly, especially if these are large systems where the effects of surge and winds are spread out over large areas as it approaches the coast.

Very true. I can attest that with Ike. Ike was really bad. The winds were long lasting for one and there was heavy rain. Ike was intensifying before landfall on Texas. As for Carla, it weakened to Category 4 with 145 mph winds. Carla was large like Ike or Katrina.

[WeatherGuesser]

it does make sense that most (not all) strong hurricanes would tend to weaken as they approach land. after all, if the storm is symetrical, half of the circulation is already over land at the time of landfall. it only makes sense that most storms would begin to degrade under such circumstances.

That's what I was thinking. We all know they degrade over land. Even the Yucatan can kill a storm at times.


Or Ike. Ike was a Category 2 when it hit Texas. A large non-major hurricane is WAY MORE dangerous than a small Category 5 hurricane. The massive storm surge leveled Bolivar Peninsula.

Ike also continued all the way up into Ohio doing heavy damage.



But then what about Charley and what he did to Florida west coast?

[wxman57]

What about Charley? Very small but intense core of winds. Minimal storm surge but a small swath of severe wind damage, just as should be expected from a tiny Cat 4 hurricane. Charley wasn't weakening as it made landfall, but it weakened steadily once inland.

Also note that the Saffir-Simpson Scale was revised last year. It's now officially the Saffir-Simpson Hurricane Wind Scale. Thankfully, all mention of potential storm surge by category was removed and it's now as it was originally designed, just a wind scale. Storm surge is not really a function of max sustained wind, it's mostly a function of wind field size and coastal bathymetry and shape (i.e., where the hurricane hits).