A note about storm surge

[Derek Ortt]

I am starting this as its own thread so it does not get buried

There is no such thing as a category 5 surge. A cat 3 that weakens does not produce a greater surge than one that intensifies

what determines the surge is the extent of the gale, storm, and ESPECIALLY hurricane force winds. If this grows to have cane winds 100 miles east of the center, wont matter if it strikes as a 3 or a 5. You're looking at more than 20-25 feet for Louisiana

[jude]

Thank you.
it bears repeating
and repeating
and repeating

[Derek Ortt]

and to note, this is growing in size. For those on the coast, do not concern yourself with the storm category

[mathwhizz]

Derek, do you know what is the line of demarcation is so to speak between New Orleans going under water and being OK?

Does Gustov have to pass 50 miles west, 75 miles, 100 miles? What are the surge scenarios for New Orleans and Louisiana?

[Derek Ortt]

passing 50 miles west will be bad... you'll have a long fetch of hurricne winds driving water up the MS River

[jcool]

How high of a storm surge can we expect along MS coast....esp eastern end (Jackson County) if along current track ? Thanks

[PTPatrick]

JCool...I would say get out of Pascagoula or Moss point if you are south of HWY 90...and if you live in east Jackson County near a river(even north of I-10). Surge could be as much as 15 ft in Pascagoula...esp if storm comes in over Plaquemines. At this point I would expect a surge greater than Betsy in Pascagoula, which was about 9 ft and a little less than Georges...which was 15 ft at my folks house in Bayou Cumbest.

[jcool]

Thanks PT... I'm high and dry in vancleave but worried about mom's house in gautier where she has a clear view of horn island from her front porch.

[PTPatrick]

Hmm...it just depends. I would think a George type surge would be the worst case senario if the current forcast hold til landfall...probably a hair less than Georges. Those bayou's down in Gautier REALLY took a lot of water in Georges. I would expect around 10 ft though to take a rough guess.

[VeniceInlet]

How are surge levels predicted? I know this might be a complex question but I have often wondered about this especially living in sw Florida 11 feet above sea level, half a mile from the Gulf as the crow flies.

I also wonder if there is a "maximum" storm surge amount that could happen in any given area. I'd like to be able to find out how high the waters could get in my house in a worst case scenario. It's a question I've never been able to find an answer to.

If we are not to look at category numbers to judge storm surge, then it seems odd that we have our local evacuation maps based on categories. I am in a cat 2 evacuation zone.

[HurricaneBill]

Another important thing:

People keep saying they hope Gustav will collapse like Lili.

Even though Lili fell apart prior to landfall, she still brought a 12ft storm surge into Vermillion Parish.

[physicx07]

I don't know if I should have started another thread, but I'd like to hear what people say about the surge threat with Gustav. It seems that at this point, the windfield has been expanding. I've also heard that a larger wind field, not just the maximum intensity, makes for a worse surge. Also, I've checked out the surge forecast on the NHC webpage, and all it shows are probabilities of a 5 ft above normal tide surge. On wxunderground, you can pick the height (3ft, 5ft, 10ft, etc) and it will show the odds of surge being higher than that. Or the 10% exceedence.

At this point the surge forecast is suggesting that maximum impact will be north of the mouth of the Mississippi river, but south of lake Borgne. If the wind field radii continue to expand, could it push the point of maximum impact farther north than it is now, or would it simply increase the expected height of surge, and it would keep the same general distribution that is already forecast? Hope that was clear enough.

Also, since the max surge is expected so close to Lake Borgne, what do you think is going to happen in Lake Pontchartrain?

[DanKellFla]

Another important thing:

People keep saying they hope Gustav will collapse like Lili.

Even though Lili fell apart prior to landfall, she still brought a 12ft storm surge into Vermillion Parish.

Good point, unlike wind, water has a great deal of mass. Once all that water is moving, it isn't going to just stop. If Gustav would disappear, the surge would still be there.

[mitchell]

Derek, do you know what is the line of demarcation is so to speak between New Orleans going under water and being OK?

Thats pretty much the $64,000 question isn't it? Gustav has passed, and i would say your question is still pretty much unanswered. Hydrology and hydraulics is a complicated science, and New Orleans is has a more complicated set of flow paths than nearly anywhere. Overtopping and breaches are very different things and many of the canal levees in New Orleans have different design storm heights.

[mitchell]

I also wonder if there is a "maximum" storm surge amount that could happen in any given area. I'd like to be able to find out how high the waters could get in my house in a worst case scenario. It's a question I've never been able to find an answer to.

"worst case" or "maximum" coastal surge is generally not quantified, as Probable Maximum Precipitation (PMP) is for rainfall and dam modellling. Also, beware of the delineation of the cat 1, cat 2 etc. surge area maps. They are known to be based on relatively "coarse" topo in many areas, and when 30 year old 5 or 10 foot contour interval USGS maps are used, the old "garbage in, garbage out" adage applies.

[Frank2]

From what I recall hearing from Brian Jarvinen, who worked on the SLOSH model, storm surge is also greatly dependent on forward speed and intensity - both of which were reduced during Ike's passage over the Gulf, so, it would make sense that since it did not strengthen beyond a Category 2 (until the last hour or so) and was moving at a consistent 12 mph (until the last hour or so), as a result, the mound of water ahead of Ike did not have a chance to build as high as in the case of Katrina, which was moving faster and was a Category 5 for many hours prior to weakening before striking the coast...

It really makes sense since the surge has time to spread out in a weaker and slower moving system, versus a fast moving and much more power system which forces the surge towards the coast - perhaps that explains the many reports of slow-rising high water in the 24-48 hours before Ike made landfall, versus Katrina, which, by my recollection, did not see high water rises until the last 12-18 hours before landfall, and, in a much smaller area, versus the water rises along many miles of coastline in the case of Ike...

Frank

[KWT]

Frank, I believe the highest surge was every bit as high as it was for Ike as it was for Katrina, just that the huge surge ended up going into a much lower densely populated region. Still take a look at the extreme damage from say Crystal beach and its very comparable to what we saw with Katrina in MS.

[Frank2]

I'd agree, but, per this article, the surge was less - the Hurricane Research Division also ran a model yesterday and determined the surge was the height mentioned in the article:

http://www.cnn.com/2008/US/weather/09/1 ... index.html

in Katrina, it was estimated at 33 feet, if I'm not mistaken, so, more than double what was seen yesterday...

Still, as you said, the damage is severe, though very fortunately mostly in lower-populated areas, as you mentioned...

[VeniceInlet]

I really want to understand surge better. I know that the Cat 2 designation for my area is meaningless. I'd like to know how high the surge would have to be in order for water to start coming into my house. And I'd also like to know how far inland in this area that an Ike or a Katrina-like surge would come, and how deep it would be in various places inland. I'd like to know this for a direct hit and for a Tampa or Port Charlotte hit. I'd also like to know how long a surge typically lasts if the hurricane is still over water or if it goes inland.

I'd also like to know how vulnerable this area is vs. TX vs MS to surge due to gradual depth changes into the Gulf, and I'd like to find out what a "worst case scenario" would look like for this area because our local met made a statement about ten years ago that I still remember that said our surge height here would be limited...can't remember what the limit was or why.

It's not that I agree/disagree/want to argue about it, and I know I won't get answers about all of this here, I'm just curious about what could happen and how it all works.

[Sanibel]

You can see the difference between a surge hurricane and a narrow non-surge hurricane like Charley. We are identical to Bolivar here on Sanibel.