question: given a major hurricane approaching louisiana.....

[weatherwindow]

what track would yield the worst problem for new orleans: head on from the south, somewhat west, or some combination?....any thoughts?

[Sanibel]

The worst case scenario for New Orleans is a weak cyclone that intensifies unexpectedly as it approaches the coast.

A slow-moving, rapidly-intensifying hurricane that comes in from the SE and tracks with its eyewall just to the east of downtown.

Combine all these with a heavy rainer and you have New Orlean's nightmare. The thing to think about is that this is entirely possible and will eventually happen some day...

Second worst case is an Allison-type storm that sits and dumps over the city until it floods out just from rain alone...

[Derek Ortt]

the worst for new orleans is actually from the due east, because the storm will make landfall directly in the city, not down in boothville, 60 miles to the SE.


A storm like Elena, a little to the south, would be the worst case

[wxman57]

the worst for new orleans is actually from the due east, because the storm will make landfall directly in the city, not down in boothville, 60 miles to the SE.


A storm like Elena, a little to the south, would be the worst case

A couple of points. First of all, there really isn't any "land" south of New Orleans. About the only land between New Orleans and Boothville are those levees. So, a northwest track toward New Orleans wouldn't allow for much weakening over "land".

Second, to get the maximum effects from a hurricane there, it will take a long fetch across the water (i.e., E-SE wind) before the storm moves ashore. Elena wasn't as bad as it could be because the easterly track meant NE-ENE winds pre-storm. Such flow didn't produce any "set-up tide" across southeast Louisiana like a storm approaching from the southeast would. You need to have that prolonged ESE-SE wind into Chandeleur sound to build up the water levels pre storm and to get the maximum storm surge into the city.

[TS Zack]

As everyone can see three different people three different aspects. Put it this way New Orleans cannot take a direct hit from a Major Cane I don't care which direction. The worst case is taking a hit from a Major Hurricane. Comes in from the Southwest stll surge into the Lake then into the city. Up the Mouth of the Mississippi is another bad scenario with all that water being pushed up the river. During Betsy a river is supposed to flow downstream well the river was flowing upstream. From the East another tidal surge into the Lake flooding the city.

The worst case is every which direction and the best case is stay away.

[MGC]

A hurricane with a large circulation like Ivan at Cat 3 or higher, slowly approaching SE La from the SE. As the tides build up in Lake Pontchatrain to 15+ feet, the winds switch around to the north puching the lake over the levees. The water would then be trapped by the levees in the city.......MGC

[Derek Ortt]

<i>A couple of points. First of all, there really isn't any "land" south of New Orleans. About the only land between New Orleans and Boothville are those levees. So, a northwest track toward New Orleans wouldn't allow for much weakening over "land".

Second, to get the maximum effects from a hurricane there, it will take a long fetch across the water (i.e., E-SE wind) before the storm moves ashore. Elena wasn't as bad as it could be because the easterly track meant NE-ENE winds pre-storm. Such flow didn't produce any "set-up tide" across southeast Louisiana like a storm approaching from the southeast would. You need to have that prolonged ESE-SE wind into Chandeleur sound to build up the water levels pre storm and to get the maximum storm surge into the city.</i>

I am not as certain that weakening would not occur before reaching the city, mainly because of what happened with Andrew in 1992. The storm was near cat 5 at 125KT, but as it moved slowly inland, the winds dropped off to 100KT at landfall, even though it was interacting with southern Louisiana. If there is more "land" there, then I am mistaken. While the surge may be worse from the SE due to the longer effects, if we see a wind reduction like we saw with Andrew, the wind damage in the city would be much less from the SE than the east. I never though 15-20KT of wind increase would mean about twice the damage, but after Frances and Jeanne, that wind reduction may save some of the high rises.

[Sanibel]

MGC is correct. I changed my post. The eye would have to cross east of downtown in order to push the surge over the Ponchartrain Levee. First the lake fills from the SE-E winds during the approach and then surges over when the eye's north winds pass over the lake as it crosses. I read a 'National Geographic' article showing a man with a 25 foot measuring pole down in the French Quarter next to some nice iron-railing houses. The caption said this would be the water depth in this place in the worst case scenario...

[TS Zack]

Actually even if the eye would past West the surge would still be so high that it would top the levees. Derek I live down here and they have some land. Mainly all marsh with lakes here and there but mainly marsh. The further West you go more towards Houma it is more land. Weakening would begin with no interaction with the Gulf Of Mexico water but still some water to maintain strength and marsh is only short grass in water therefore the winds wouldn't drop as fast.

You can sit here and dispute but the only answer is when Mother Nature does it. So many different things can happen with a large curculation but a Cat 2 or a huge surge but only a Cat 1. Look at it this way any Hurricane over 100mph winds everyone in New Orleans should leave, if not don't expect to have all your things with you as you go through the Hurricane then after. The big thing isn't the storm it is after when all that water is trapped and then you have snakes, other animals trying to survive plus disease will come about as the heat returns.

This will not be a place to want to be or see.

Therefore anyone in New Orleans it is in your best interest to get out.

[Huckster]

<i>A couple of points. First of all, there really isn't any "land" south of New Orleans. About the only land between New Orleans and Boothville are those levees. So, a northwest track toward New Orleans wouldn't allow for much weakening over "land".

Second, to get the maximum effects from a hurricane there, it will take a long fetch across the water (i.e., E-SE wind) before the storm moves ashore. Elena wasn't as bad as it could be because the easterly track meant NE-ENE winds pre-storm. Such flow didn't produce any "set-up tide" across southeast Louisiana like a storm approaching from the southeast would. You need to have that prolonged ESE-SE wind into Chandeleur sound to build up the water levels pre storm and to get the maximum storm surge into the city.</i>

I am not as certain that weakening would not occur before reaching the city, mainly because of what happened with Andrew in 1992. The storm was near cat 5 at 125KT, but as it moved slowly inland, the winds dropped off to 100KT at landfall, even though it was interacting with southern Louisiana. If there is more "land" there, then I am mistaken. While the surge may be worse from the SE due to the longer effects, if we see a wind reduction like we saw with Andrew, the wind damage in the city would be much less from the SE than the east. I never though 15-20KT of wind increase would mean about twice the damage, but after Frances and Jeanne, that wind reduction may save some of the high rises.

This question of marsh and its role in hurricane intensity has intrigued me for a while. If marsh/swamp/lakes are going to have a tempering effect on weakening, in Louisiana, that effect, in my opinion would be most noticable in SE Louisiana, as opposed to SW Louisiana. Why? Both sections are nearly completely covered in water and lakes. However SE Louisiana is much less defined than SW Louisiana. The SE part of the state is very fractured by bays, lakes, inlets, etc. That's not to say the SW part doesn't have its share. It simply does not have the same volume. Lakes Pontchartrain, Maurepas, Salvador, Des Allemands, Borgne are just a few of the rather large lakes in the SE. Add to that the myriad smaller lakes, canals, etc.

Though I've lived here in LA my whole life, I am only 22, so my personal experience with hurricanes is rather limited. I don't recall the first Danny, Juan, Elena, Florence, etc. However, since I have had access to computers, I've been able to track everything that has hit SE Louisiana since 1997. Now, I am speaking unscientifically here. I am just going to speak based on what I saw by looking at radar mainly. SE Louisiana apparently had little or no effect on Danny in 1997 when it cut across Delta region. I was amazed in 2002 when Isidore appeared to get better organized during the first hour or so after landfall. It certainly did not rapidly fill in. It seemed to maintain or even better organize some sort of eye wall structure. I noticed the same thing for Bill in 2003. Bill definitely maintained intensity anomalously well as it moved NE toward Lakes Pontchartrain and Maurepas. I actually drove directly into the center of Bill as it was moving across those lakes, over St. John the Baptist Parish, and Bill definitely had an eye of sorts, much more than most tropical storms would have, having been inland for a couple or more hours. While driving, I definitely encountered very heavy rains and high winds that increased toward the center until I came to a bright clearing where the winds completely stopped. Even all the water along I-55 became like a mirror. I could definitely see that I was surrounded by a circular ring of clouds, open to the S. Once it got north of the lakes, into the higher, drier lands of the E. Gulf Coastal Plain, it started to fill in pretty rapidly.

I am not saying that every storm which hits LA is going to behave the same way. I do believe though, that given the right conditions, storms moving across SE Louisiana definitely benefit from the effects of the tremendous open water area and land covered with water here, lakes and marsh.

It didn't seem to help Lili at all. But, Lili was rapidly weakening before it ever hit. Also, it hit the SW part of the state, which like I mentioned, may not have as much of an effect.

Andrew also didn't seem to be much affected. I know Andrew was very strong on its approach to Louisiana, but it started weakening before it ever hit. I think this may have been due to dry air. That's what it looks like to me, based on some satellite pics I have seen, before the eye even makes it ashore. Andrew also tended to go more toward the SW part of the state, actually, more central, just west of Morgan City. There's not nearly as much water in that region as there is just a little farther east. Not saying Morgan City is dry, just that the effects there might not be as noticable as they would have been had the storm come in at Grand Isle. I guess someone could always argue that Andrew might have weakened even more rapidly than it did, if the land was high, dry, and hilly like NW LA.

I can't speculate on all the complex physics and so on that would be require to completely understand this issue. I am mostly going by personal experience in obsessively tracking storms here and elsewhere. I can't say I've seen storms hitting other states act quite like the ones here. The most I can say is that there are at least some people of consequence who might agree that what I am saying has merit. See the comments on the 1893 storm re-analysis here:

http://www.aoml.noaa.gov/hrd/hurdat/metadata_91-00.html#1893_8

And also on Hurricane Betsy here (scroll down about 1/3 of the way):

http://www.aoml.noaa.gov/hrd/hurdat/august01/rpibook-jan03.htm

If this is all true, this effect will only get worse in years to come. With LA losing around 25 sq. miles of land per year, another 1915, 1947, or Betsy would be much worse today.

[TS Zack]

Land is going completely Bye Bye in La. This is definitely not in any of our times but we got to think about our kids, kids. We are trying to save them so they can enjoy what we enjoy today with the fishing and hunting and beautiful areas of SE La.

Huckster have you ever seen a map of the projected land in La by 2100.

I will just say Hello New Orleans the Island with roads and levees.

[Stratosphere747]

Huckster......

That was one excellent post....

[Kennethb]

Just about any storm with a direct hit on New Orleans will have the potential to flood the city.

I recall seeing a model and also seeing a map showing the worst case scenerio that would be from a Cat 3 or above moving slowly NE. A storm slowly approaching from the SW would produce an east fetch for several days which would pile water into Lake Ponchartrain. Then as the storm hit the water would pour into the city.

Remember that the highest tide levels recorded in east Louisiana was not from Camille, Betsy, or Andrew, but from Juan in 1985. It was only a weak Cat 1 but meandered around for several days.

[Hurricane_Apu]

Allison also intensified over S. Louisiana... it reached its peak intensity... <1000 MB and very near hurricane strength... while over land.

Of course Allison was a hybrid... and overall a rather freakish storm...

[LSU2001]

As weak as Matthew was it still caused some flooding around Ponchatrain and Maurapas. A Real storm passing very close to NOLA would cause extreme flooding and would create havoc even on the north shore. I think that to really know what is "worst Case" we would have to see it unfold.
Tim

[Ixolib]

A storm with a persistent track approaching from the extreme SE Gulf, crossing the lower Chandeleur Islands on path NE across Breton Sound, over the marsh (with the eye coming over E. New Orleans), and ultimtely into the lake just a mile or so NE of the city would be the worst case.

[wxmann_91]

Sorry to resurrect this thread, but with the recent scare of Hurricane Dennis and the hot waters of the Gulf coast, might want to. Even Ivan last year produced enough surge in Lake Pontratrain to cause minor flooding in the greater New Orleans area. So IMO a hurricane as strong and large as Ivan could, in fact, even if it hit Mississippi, cause major surge damage in New Orleans.

My worst case scenario:

[Steve]

Doomsday is a storm coming in from the East-Southeast passing just south of the city is the true catastrophic scenario. Then again, so is a storm coming up from the south, SE, SW or whatever if it's strong. But the track across the westbank where the surge moves into the lake and empties into the city floods it temporarily beyond repair.

Steve

[HurryKane]

http://www.nola.com/hurricane/?/washingaway/

[wx247]

Excellent link. Thanks!