Mississippi SLOSH models

[f5]

according to the SLOSH model what was the highest possable surge on the coast?

[wxman57]

according to the SLOSH model what was the highest possable surge on the coast?

I ran the SLOSH "MEOW" model (Maximum Envelope Of Water) for a Cat 5 movning due north into various points along the MS coast. The peak was about 30 feet just west of Gulfport - where Katrina came ashore. However, this version of SLOSH uses an average-sized hurricane and there are multiple landfall points. I did not create a special Katrina storm with the much larger wind field to calculate storm surge.

[f5]

can i call her a Tsunami?

[Dr. Jonah Rainwater]

What's the record for the largest (windfield) hurricane in the Atlantic basin? Because while Katrina was very large, Category Fives tend to come in two types: tightly wound tornado-like bombers like Andrew, Camille, and Labor Day...and then the monsters like Katrina, Rita, Mitch, Allen, Gilbert...etc. It's really not that unusual at all for a Category Five storm to be over 300 or 400 miles across...you don't just take your average Cat3 like Jeanne and stick some 175mph winds into the center.

I actually think that the SLOSH models are probably outdated, because we just don't know that much about Category 5 hurricanes and what they can do, because they're so rare. (or used to be so rare, anyway)

[MGC]

So, how does the SLOSH model explain a large wind field Cat 3 moving rather quickly producing a 30+ feet surge? I've looked at the models and never saw that......MGC

[f5]

put Katrina over texas to get a good size estimation

[Derek Ortt]

That 30 foot for an averaged size cat 5 is very interesting for the Camielle intensity debate.

We know that Camielle was an average to above average sized hurricane based upon its windfield at landfall. It only produced a 24 foot surge.

This should be further investigated so that the record can be corrected if there is an error, to avoid a repeat of Katrina along the MS Coast.

[gpickett00]

It only produced a 24 foot surge.

I'm pretty sure that is the first time I have ever heard "only 24 foot surge"

[Derek Ortt]

I know, I know

only and 24 foot surge do not go along well, except when compared to 30

One note: We know that Camielle, like Katrina was weakening as it approached the coast as the pressure was rising, likely reducing the pressure gradient. Its intensity when it reached the shelf may be of more use than its landfall intensity. Katrina hit the shelf as a strong 4, but land as likely a marginal 3. Unlike in the cases of Ivan and Opal, the weakening occurred once over the shelf, not after, too late to reduce the surge. I suspect something similar happened with Camielle, but am not sure due to the lack of available recon data to properly analyze

[f5]

I know, I know

only and 24 foot surge do not go along well, except when compared to 30

One note: We know that Camielle, like Katrina was weakening as it approached the coast as the pressure was rising, likely reducing the pressure gradient. Its intensity when it reached the shelf may be of more use than its landfall intensity. Katrina hit the shelf as a strong 4, but land as likely a marginal 3. Unlike in the cases of Ivan and Opal, the weakening occurred once over the shelf, not after, too late to reduce the surge. I suspect something similar happened with Camielle, but am not sure due to the lack of available recon data to properly analyze

i don't think it matters Katrina filled up the entire central gulf from the southern louisiana coast to the yucatan she was also pushing water up when she was a CAT 5 165 or CAT 4 155

[Derek Ortt]

the max open ocean surge is about 3 feet. The water excapes from below, meaning the open ocean surge is almost entirely due to the low pressure. The wave height is a function of how strong the storm was over the open ocean, if the storm moves at the same speed as the waves. But the overall storm surge is not that dependent upon its intensity in the open ocean

[Ixolib]

...Unlike in the cases of Ivan and Opal, the weakening occurred once over the shelf, not after, too late to reduce the surge...

And therein lies the gem of knowledge and understanding that must be somehow effectively communicated to the general public when advising them of a potential landfalling hurricane. The "officials" must figure out what methodology and modeling they will employ by the '06 season (if not sooner) to ensure the threatened public places as much attention on the "surge factor" - and its potential - as they place on the "wind factor".

Once a greater understanding and education of this phenomena is firmly entrenched in the public domain, I believe many more lives will be saved. But it's going to take a herculean and on-going effort to bring it to fruition.

I also believe the SSS ought to be reshaped, in fact, to place the emphasis of surge at the forefront instead of as an addendum. It should also use the highest possibility as the mark instead of a range. For instance, for Katrina (I believe) the advisory stated: surge 18-22 feet with 28 feet locally. IMO, the advisory should have simply said expected surge is 28 feet, and leave all the "other" range possibilities out. Doing otherwise lulls many in the warned area to assume that "locally" must mean someplace else.

It certainly "lulled" me, and because I'm a regular visitor to S2K, I'm most probably better educated on hurricanes than John Q. Citizen. In my mind, the "22 feet" or less is what I was keying on. Dumb or not, that was the reality for me, and for many others I presume...

p.s. - I also believe wave heights on top of the surge ought to be equally communicated and emphasized along with the surge advise. Even above the advice give for wind speed.

[Derek Ortt]

I agree that the wave forecasts should be stated more clearly

I disagree with emphasizing the max tidal surge heights, but would like the following line added

<b>Tidal surge in the heads of bays and rivers may reach heights several feet above that experienced on the immediate coastline.</b>

[Ixolib]

I agree that the wave forecasts should be stated more clearly

I disagree with emphasizing the max tidal surge heights, but would like the following line added

<b>Tidal surge in the heads of bays and rivers may reach heights several feet above that experienced on the immediate coastline.</b>

What would be gained (or lost) by NOT emphasizing just the the max and leaving the other "alternatives" out?

And I'll agree with your point about the head of a bay, but NO ONE in these parts ever utilizes that phrase as a term of reference. In fact, the "bays" here (Biloxi and Bay St. Louis) are both viewed by the locals as nothing more than extensions of the MS Sound (aka GOM). Right or wrong, that's how they see 'em, especially BSL. Of course, I'm all for re-educating the public on MANY of these hurricane related issues.

By the way, many of the rivers here on the coast barely reached flood stage with Katrina - surge "up the river" was not nearly as significant a problem as the coastal result would indicate.

Perhaps it might be more telling if every coastal resident within XX miles of the coastline knew exactly, via official measurements, where their specific property is in relation to mean sea level. Having that knowledge would enable them to react accordingly to both surge AND wave advisories. For instance, I'd like to get an official letter from my municipality that points out - in concrete terms - how many feet and inches my property (say, the driveway) is above MSL. Having that info would not only allow me to make better informed decisions, it would also give the cities and counties the ability to perform mandatory evacuations on a more realistic and enforceable basis.

[Downdraft]

Question for Derek and others. Is it possible that once a storm becomes a strong cat 4 or cat 5 as it approaches the coastline the surge will stay at the level even if the storm does not? I mean the energy potential of moving a body of water along to form the surge does not dissipate as quickly as the wind field. Would that explain why we see record surges still hitting the coastline although the storm itself is weakening as it approaches. I would imagine that once you get such a large mass of anything (water having weight) moving that it continues long after the winds above have decreased in strength. Intertia gives momentum and physics says an object in motion tends to remain in motion. If this is true we need to rethink our surge warnings for Cat 3 storms approaching the coast that have previously been strong cat 4's or a 5.

[thunderchief]

I think the real problem is that people got complacent... storm surge always used to be the #1 danger but then improved forecasting, public education, and probably some luck, drastically reduced storm surge deaths, to the point where freshwater flooding and idiotic accidents were the 'big' killers. People had forgotten what surge could do, especially with the massive growth of the southeast coastal populations that had yet to live through anything close to Camille, the last epic surge storm, 36 years ago.


The majors of the past few decades pushed up a storm tide that took out some beachfront homes that had wisely been evacced, but werent even close to what could have been. Then comes Katrina, throws ashore a ~30 foot surge wiping away an extensive area well inland and killing more than 1000 people, and now surge is back in the public eye.

[Ixolib]

Question for Derek and others. Is it possible that once a storm becomes a strong cat 4 or cat 5 as it approaches the coastline the surge will stay at the level even if the storm does not? I mean the energy potential of moving a body of water along to form the surge does not dissipate as quickly as the wind field. Would that explain why we see record surges still hitting the coastline although the storm itself is weakening as it approaches. I would imagine that once you get such a large mass of anything (water having weight) moving that it continues long after the winds above have decreased in strength. Intertia gives momentum and physics says an object in motion tends to remain in motion.

If this is true we need to rethink our surge warnings for Cat 3 storms approaching the coast that have previously been strong cat 4's or a 5.

Now that is truly hitting the nail on the head!! This post, and the one below it from Thunderchief, point out some real opportunities for educating and re-educating the coastal public. I agree, surge warnings need an overhaul and should surely point out in the advisories how weakening winds DO NOT mean weakening surge. And as for complacency, it is high time that the NWS/NHC/TPC/etc set out on a concentrated and directed campaign to educate the public. Instead of National Hurricane Week, they should have National Hurricane Quarter that runs from April to June, and just saturate the airways, internet, and print media with the "new and improved" information.

[Derek Ortt]

the open Ocean really does not matter for mean water rise. Ivan produced a typical cat 3 tidal surge, as did Opal. Differnece between thet wo was the height of Opals surge was east of the more heavinly populated Pensacola area.

Isabel produced the tidal surge heights typical of a landfalling cat 2

shelf intensity does seem to matter

[Recurve]

Perhaps it might be more telling if every coastal resident within XX miles of the coastline knew exactly, via official measurements, where their specific property is in relation to mean sea level. Having that knowledge would enable them to react accordingly to both surge AND wave advisories. For instance, I'd like to get an official letter from my municipality that points out - in concrete terms - how many feet and inches my property (say, the driveway) is above MSL. Having that info would not only allow me to make better informed decisions, it would also give the cities and counties the ability to perform mandatory evacuations on a more realistic and enforceable basis.

Everybody living coastally should know the exact elevation of their property. But that requires a survey by a licensed surveyor. Municipalities aren't going to have the data to give to residents. Not that a town couldn't decide to spend the money on surveying and making the information available. But elevation is a critical legal benchmark for real property, as much as the boundaries and any liens or obstructions. I would expect towns to stay away from saying what the elevation of each individual lot is.

OTOH, you should be able to look at Federal Flood Insurance zone maps and see the general elevation of your lot. Flood zone map should show the average elevation and the base flood height; you are prohibited from building habitatable space below base flood if you want federal flood insurance, and, in most areas, a building permit. I don't know what category storm the flood height is based on.

This summer may show that we need to spend more on research and modeling to produce new, more accurate flood maps too.

[weatherwindow]

I know, I know......

only and 24 foot surge do not go along well, except when compared to 30

One note: We know that Camielle, like Katrina was weakening as it approached the coast as the pressure was rising, likely reducing the pressure gradient. Its intensity when it reached the shelf may be of more use than its landfall intensity. Katrina hit the shelf as a strong 4, but land as likely a marginal 3. Unlike in the cases of Ivan and Opal, the weakening occurred once over the shelf, not after, too late to reduce the surge. I suspect something similar happened with Camielle, but am not sure due to the lack of available recon data to properly analyze

....agreed, derek...those surge values,~9-10 meters, were a function of the windfield of katrina as a cat 4/5...not the cat3 strength at landfall. as to camielle, i dont remember seeing a recon fix over the shelf..do you have it?.......rich