"The Big One for the Big Easy" by Mike Naso

[Derek Ortt]

andrew then weakened 30KT over the marsh in just 3 hours, same rate as did Charley

[Scott_inVA]

So how could a 4 or 5 have a direct hit on New Orleans???

I think it's possible..

I think it is too, which is why I asked. He said it would weaken over the swamps which was always the way I thought it would come in. New Orleans isn't oceanfront like Miami.

Interesting speculative discussion but one critical component is missing...forward speed. All things equal, NOLA gets crushed by a major TC moving at >25MPH. A hurricane slogging along at 10-15MPH would in all liklihood do less damage.

Scott

[SouthernWx]

So how could a 4 or 5 have a direct hit on New Orleans???

Yes...definitely.

I respectfully disagree with the gentleman who stated Betsy weakened so dramatically between the GOM and New Orleans.

To begin with, hurricane Betsy didn't pass directly over New Orleans...the path was from landfall near Grand Isle toward Baton Rouge. Even though Betsy was a large hurricane, and hurricane conditions occurred in greater New Orleans (especially significant storm surge flooding of 10' or more)...the true core didn't impact the city (and still 58 people died in Orleans Parish alone; 75 statewide).

If Betsy had moved north or NNW and passed just west of or over New Orleans, there's no doubt in my mind that peak gusts around the Crescent City would have exceeded 140 mph...possibly 150+. It's a lot farther from Baton Rouge to the open GOM than from New Orleans, and Betsy still produced winds over 100 mph there and caused extensive damage in Louisiana's capitol.

If that isn't proof enough, consider this: in 1969, hurricane Camille made landfall along the Mississippi Coast with 175-180 mph sustained winds. Look at a Mississippi map....find a small town called Columbia; it's WSW of Hattiesburg. When Camille reached Columbia, Mississippi, a private anemometer owned by James Thornhill recorded sustained winds of 120 mph with peak gusts estimated near 140 mph (after the anemometer was destroyed at 135 mph).

As you can see from the map, it's a heckuva lot farther from the Mississippi Coast to Columbia, MS than it is from Bourbon Street to the open Gulf. If Camille had made landfall just west of Boothville....then moved NNW at 16 kt to near/ just west of downtown New Orleans, IMO the city would have ceased to exist; gusts would have exceeded 160 mph, and water would have filled downtown New Orleans three stories deep.

Anyone living in greater New Orleans...don't believe a hurricane will weaken two categories between you and Grand Isle (or Buras); an intense hurricane takes a long time to wind down once inland, especially if it's moving 15-20 mph or more. Even though Betsy missed the city by over 40 miles, dozens still died there...mostly by drowning. That was the last direct hit by a major hurricane on the Crescent City.....40 long years ago; IMHO it's been far too lucky for too long

PW

[SouthernWx]

from the east it wont but the south, it will

if you would read any scientific modeling studies, you would know

Friend, it wouldn't weaken as much as you think. There's no doubt in my mind if a 125 kt cat-4 makes landfall near Grand Isle and moves north, it will obliterate the city of New Orleans. In fact, if it's a large cat-4 in the mold of Hugo or Carla, winds will already be gusting over 110 mph on Bourbon Street BEFORE the eye ever crosses the coast south of the city.

Model data is good, but unfortunately it has a difficult time forecasting something that hasn't happened; unless it's "tested under battle conditions".
There hasn't been a really monstrous hurricane into New Orleans (the core eyewall region) in a very long time. Betsy missed by 40 miles, the 1947 hurricane was weakening; never truly recovered from its passage over S FL...was barely a cat-3, the 1915 hurricane was weakening (it was almost October).

Andrew was a fairly small hurricane, it skirted along the coast, plus the fact it was slowing to recurve....it didn't come blasting ashore like Betsy and Camille did at 15-20 mph. If a 145 mph cat-4 slams into the marshes east of Grand Isle and moves NNW at 15 mph, IMO you can write off New Orleans as a major city for many years; it won't weaken that much....not enough to matter anyway (esp. from a storm surge and flooding perspective).

[Derek Ortt]

surge will still be as bad (surge won't decrease quickly due to cat reduction) but the winds may enough to allow for vertical evac)

[Valkhorn]

Friend, it wouldn't weaken as much as you think. There's no doubt in my mind if a 125 kt cat-4 makes landfall near Grand Isle and moves north, it will obliterate the city of New Orleans. In fact, if it's a large cat-4 in the mold of Hugo or Carla, winds will already be gusting over 110 mph on Bourbon Street BEFORE the eye ever crosses the coast south of the city.

Model data is good, but unfortunately it has a difficult time forecasting something that hasn't happened; unless it's "tested under battle conditions".
There hasn't been a really monstrous hurricane into New Orleans (the core eyewall region) in a very long time. Betsy missed by 40 miles, the 1947 hurricane was weakening; never truly recovered from its passage over S FL...was barely a cat-3, the 1915 hurricane was weakening (it was almost October).

Andrew was a fairly small hurricane, it skirted along the coast, plus the fact it was slowing to recurve....it didn't come blasting ashore like Betsy and Camille did at 15-20 mph. If a 145 mph cat-4 slams into the marshes east of Grand Isle and moves NNW at 15 mph, IMO you can write off New Orleans as a major city for many years; it won't weaken that much....not enough to matter anyway (esp. from a storm surge and flooding perspective).

I tend to agree. No matter what study you want to put in front of us there has never been any observed storm travelling over it's own storm surge to the degree that something like this could do.

Until it happens, guessing is all you can really do.

[MGC]

I'm with SouthernWx on this argument. Andrew crossed land and still intensified. A hurricane approaching New Orleans won't hit solid land till it reach north of Lake Ponchatrain. South of the lake offers little to weaken a hurricane. Sure it might weaken a little but not much. Little in the way of friction to rapidly spin down the winds. What little land is there will be coverered by water.....MGC

[Matt-hurricanewatcher]

Tropical storm Bill(2003) on Radar was still oreganizing has it moved into this area. The radar shown a eye form. Kind of Like Gastav. I say that reached its peak as it was moving on land or just onland. Kind of like Andrew as it was moving in. It was bombing.

[Derek Ortt]

you guys are forgetting one major thing.

Its not the surge that will be the worst problem from NO, except in a strong 4 or a 5. Its the rainfall. Georges in 1998 could have been catastrophic, even though had it came into the mouth of the Mississippi, it really would have had no chance to be a cat 2 into NO (remember, those strongest winds only affect the very immediate coast, the winds are about 10-20% weaker just 3-5 miles inland). However, the 30-40 inches of rain it would have brought into the city would have been sufficient to flood large portions of it

[Matt-hurricanewatcher]

I always thought what would do New orleans in is a storm Surge rising over into the city. Or over the storm wall. Rememeber a strong cat5 hurricane would have 20 to 25 foot surge. That would flood New orleans under 30 to 50 feet of water.

[tallywx]

Plus, one also has to consider how much "non-ocean" is left south of New Orleans. The answer: not much.

From the Washington Post: "On a seaplane tour of the region Tuesday, Gerald M. Duszynski, assistant secretary of the Louisiana Department of Natural Resources, pointed out an area near the tiny bayou town of Leesville, where he fished for redfish and flounder 25 years ago. Once a solid patch of green tidal marsh, it is now mostly open water, with a few strips and splotches of green.

"This used to be perfect, and now look at it," Duszynski said. "The buffer is gone. Now even the little storms give a big influx."

"Southern Louisiana is sinking into the Gulf, losing about 24 square miles of coastal marshes and barrier islands every year. Those marshes and islands used to help slow storms as they approached New Orleans; computer simulations now predict that the loss of these natural storm barriers will increase storm surges and waves by several feet. "

----

If you look at a recent landsat image, you basically have open water from New Orleans south of the Gulf now. A storm surge carried by a cat 4 hurricane moving in from the south will create open ocean all the way from what was once the "shore" straight up to New Orleans.

link to landsat:
http://maps.google.com/maps?q=new+orlea ... &t=k&hl=en

[Matt-hurricanewatcher]

I heard that land south of New Orleans, about 6 months ago is going under water? I heard it on the weather channel.

[TS Zack]

Derek,

As far as the winds subsiding to allow for a Vertical Evacuation. I don't think you would really have a choice.

Pick??
No Chance and Drowning
Or
Chance Getting Hit But May Survive

[Derek Ortt]

vertical evac in a cat 4 is nothing short of suicide. The glass panes will be blown out of the buildings way up high, menaing you had better have wings

[Anonymous]

vertical evac in a cat 4 is nothing short of suicide. The glass panes will be blown out of the buildings way up high, menaing you had better have wings

Cmon' Derek. Stop being so negative and alarmist. If you vertically evacuate in a Category 4, you have an increased risk due to strong winds and flying debris. But, you can HIDE FROM THE WINDS, BUT YOU CAN'T RUN FROM THE WATER. That's the way it should be said. Cmon' Derek, you know that.

[Derek Ortt]

no, you cannot vertically evac

Do you have any idea regarding the wind profiles in a cat 4?125 at the surface equates to about 180 at the top of those buildings. If you think thats safe, by all means Mike, go up into those winds, just dont expect to me lose any sleep when you don't make it out

[Anonymous]

I know one man survived after being knocked out in 185 mph winds in the Keys in 1935. He saw sparks because the sand was hitting rocks at up to 200 mph. Yet...he lived.

If a person can cling onto a tree, they might have a chance.

[Derek Ortt]

problem is, those buildings are not going to survive, especially the glass ones that wouldn't make it through cat 1 winds, leaving people very exposed at very high elevations.

also, I meant 185KT, not m.p.h. That's a nice little F-4 tornado aloft in the max wind regime

[sunny]

problem is, those buildings are not going to survive, especially the glass ones that wouldn't make it through cat 1 winds, leaving people very exposed at very high elevations.

That was what I thought, but everyone said I was crazy. I knew a few people who went to hotels downtown rather than leave the city. Nagin was recommending "vertcal evacuations" for the people who did not leave the city for Ivan.

[Brent]

Remember that F2 tornado(I think it was) in Fort Worth a few years back? Blew out a ton of windows in the skyscrapers...