What is everyone's worst case hurricane scenario? (Ortt pg3)

[Derek Ortt]

the only good thing in that scenario is that vertical evacuation would be a viable option, unlike in a hurricane. However, millions would still die, especially in Europe where they would have very little warning

[tailgater]

IMHO It's still the Miss/ SE La. region getting hit by a INTENSTIFING CAT 4 or larger moving slowly in a more WNW motion just south of New Orleans essentually flooding the rest of the New Orleans, Gretna, Metairie,Kenner, Laplace, Houma, Slidell and lots of the North Shore.
I-10, Hwy 11, Causeway, I-55, and the I-10 east of Laplace would all probably be impassible, flood waters could reach as far NW as East Baton Rouge Parish. (see slosh models for this region). That would make it very difficult to get aide to this area. Also Most of the refineries in area would be down for sometime.
Not a very likely scenario, much like NYC getting hit with a Cat 3 or 4, which would probably worst yet.

Could someone tell me if any studies have been made on difference on Intensifying storms making landfall vs weaking ones. I would think that it would be a big difference in wind damage and a much less difference in surge and I'm not sure on rainfall.

Such an intensifying storm would create a Cat 1-2 storm surge. Look at Charley for an example of such. Also I can't see a storm intensifying while stationary on the coast; land interaction and the shelf waters would prevent such. Such would need to be a very small storm to intensify near the coast. It would be more of a wind event than anything.

To be worse than Katrina at the same intensity, it would have to be even larger (in physical size) and have to approach from the SE to drain the maximum storm surge into Lake Pontchartrain while still flooding the Mississippi coast.

Please explain why you think that would be a Cat 1 or 2 storm surge, with a Cat 4 intensifying as it moves on shore just southeast of NO moving WNW.

[Jim Cantore]

A storm like Isabel striking the Delaware Bay Area.

[docjoe]

actually the worse case scenario would be for yet another hurricane to hit Santa Rosa County. Trying to tell my wife that we get to spend yet another week without power with almost three year old twins and chopping and hauling more trees....well I would rather ride out the storm on the beach in a lounge chair!!!!!!

docjoe

[SkeetoBite]

Personally, I think something the size of Frances 2004; add in Cat 4 or higher intensity moving slowly ashore into Tampa Bay. My nightmare has the dirty side pushing water into the bay for a couple hours or more. Throw in an 80+ mile wide eye and you have the eye wall half way to Orlando before the storm is fully on shore. Obviously something this big would affect the entire state. This hypothetical landfall would also affect Georgia and South Carolina due to the size of the storm and path required for this to occur.

The slosh maps for Tampa in this scenario has the high water mark all the way inland to the I-75/I-4 interchange. While this is apparently plausible, it is hard to imagine. The city has a 3D fly though animation somewhere for this scenario. I'll post a link if I find it again.

[MiamiensisWx]

Please explain why you think that would be a Cat 1 or 2 storm surge, with a Cat 4 intensifying as it moves on shore just southeast of NO moving WNW.

In the scenario you describe (and in many other potential setups), it would depend on the extent of the windfield. A large major hurricane - intensifying, maintaining intensity, or weakening - coming in on the New Orleans area from the southeast while moving west-northwest (ala September 1947 and Elena of 1985) would undoubtedly create a large vicinity storm surge, and the angle of approach would magnify the surge heights. In addition, less loss of intensity of the storm may occur on such an approach angle due to less negative frontal interactions (and associated mid-level drier air) and potentially less upper-level shear, depending on the synoptics playing out.

Meanwhile, a smaller hurricane in terms of windfield (ala Charley of 2004 and other examples) would produce significantly less surge. Also, a rapidly intensifying miniscule storm would not allow time for the windfield (if it is slowly expanding) to gradually bring the winds down to the surface over a broader area and increase surge heights; thus, the larger the windfield expanse and the greater surge heights may occur (depending on some other geographic and synoptic factors of course).

[Cyclenall]

Here is a unique idea for a worst hurricane scenario:

All weather satellites go out and we no longer have the tools to forecast tropical cyclones posing danger to landmass. Now use your imagination to figure out what a Katrina type storm heading toward a huge city without anyone knowing about it can do. Talk about a nightmare. Just think, a category 4 hurricane making landfall on Tampa without anyone knowing about it in the middle of the night with only radars picking up the hurricane but it's too late to warn people of a massive storm coming. The death rates would skyrocket way past anything tropical cyclone related at least in North American history.

I got this idea from reading that article about aging weather satellites. This may not be out of the question if something unexpected happens either. We'd still have recon, radar, ships, etc.

[Derek Ortt]

we'd be fine without satellites. We went without them and once we got recon, the days of high death tolls were gone (except when the forecast was butchered like in Audrey, though Opal shows that it still happens from time to time)

Reread my worst case on pg 3... I do not get the impression that many grasped the underlying message of the worst case being the unexpected. Most of the others, while terrible beyond comprehension, are expected (though NYC was not until the day after Katrina took out NO). Cyclenall seems to have grasped the concept somewhat (though sats going out happens somewhat frequently, lightening has put out the sats for a few hours during the past couple of seasons

[P.K.]

The other day El Hierro which is just south of La Palma actually had some very heavy rainfall along the lines of what you were saying here Derek. The report says 500 litres per square metre fell, that is a massive 0.5m of rain in just 36 hours! See this and this. Some very bad damage there from landslides and general flooding.

[CrazyC83]

IMHO It's still the Miss/ SE La. region getting hit by a INTENSTIFING CAT 4 or larger moving slowly in a more WNW motion just south of New Orleans essentually flooding the rest of the New Orleans, Gretna, Metairie,Kenner, Laplace, Houma, Slidell and lots of the North Shore.
I-10, Hwy 11, Causeway, I-55, and the I-10 east of Laplace would all probably be impassible, flood waters could reach as far NW as East Baton Rouge Parish. (see slosh models for this region). That would make it very difficult to get aide to this area. Also Most of the refineries in area would be down for sometime.
Not a very likely scenario, much like NYC getting hit with a Cat 3 or 4, which would probably worst yet.

Could someone tell me if any studies have been made on difference on Intensifying storms making landfall vs weaking ones. I would think that it would be a big difference in wind damage and a much less difference in surge and I'm not sure on rainfall.

Such an intensifying storm would create a Cat 1-2 storm surge. Look at Charley for an example of such. Also I can't see a storm intensifying while stationary on the coast; land interaction and the shelf waters would prevent such. Such would need to be a very small storm to intensify near the coast. It would be more of a wind event than anything.

To be worse than Katrina at the same intensity, it would have to be even larger (in physical size) and have to approach from the SE to drain the maximum storm surge into Lake Pontchartrain while still flooding the Mississippi coast.

Please explain why you think that would be a Cat 1 or 2 storm surge, with a Cat 4 intensifying as it moves on shore just southeast of NO moving WNW.

If it is intensifying as it approaches land, it takes a while for the surge to catch up with the winds (and vice versa). That is why Katrina's surge was so incredibly large despite the fact it was only a Category 3.

[Lindaloo]

Andrew's damage was NOT poor construction.

That was based upon the incorrect assessment of Andrew's intensity. Andrew's damage was due to wind gusts equal to those in the Xenia Tornado (about 200 mph based upon structural analyses in Xenia). Winds at that intensity will level most anything.

It is worth noting that the last 3 cat 4 or 5 hurricanes to hit the USA (Andrew, Iniki, and Charley) were wind events. This is despite Andrew producing a 17 foot surge, and about 10 feet in Coconut Grove. That is because hurricanes of that severe intensity are basically extended violent tornadoes, with gusts approaching those in the strongest of tornadoes

Yes it was due to poor construction. Codes were not enforced at all before Andrew. The strict codes were there, but, were ignored.

There was a criminal probe into contractors that built homes after 1986 but they could not find sufficient evidence to bring charges against them when fire marshalls and inspectors were ignoring codes on new construction.

I am surprised at you Derek. All the reports I have read said that Andrew had alot of "mini swirls" and wiped out anything in their paths.

[Derek Ortt]

Linda,

I am currently living in Andrew's cat 3 zone... damage was minimal in South Miami. I was only in the cat 4 and 5 zone that we saw the damage

I did a research project for an undergrad history class on this very topic. The findings of poor construction were based upon the belief at the time that Andrew was a category 4 hurricane. Comparisions were made with Donna, which after the reanalysis remained a cat 4. The claim that Andrew's damage was due to poor construction was made by comparing Andrew's damage with Donna's. Of course Andrew's was worse, which, after we had the reanalysis, we now have the reason for it. Andrew's winds were at least 25KT HIGHER than Donna. The difference between 145 and 120KT winds is a factor of 1.46. (145^2/120^2). That is Andrew's force compared to Donna's. Nearly 50 percent more destructive power in Andrew; thus, I am not surprised at the findings of the criminal probe (Operationally, Andrew and Donna had EQUAL landfall winds)

Where did I say anything about the miniswirls not wiping out everything? I said those were Xenia tornados, so of course they wiped out everything and were what caused the damage, against casting serious doubt on the poor construction theory (unless Xenia had construction just as bad, but that would not explain the re-enforced concrete structures)

All I can say about Andrew is that I am glad I was not in Miami then. Wilma was bad enough and it took a while to get over the initial scenes when I finally left the Rickenbacker Causeway that Monday afternoon

[Derek Ortt]

If it is intensifying as it approaches land, it takes a while for the surge to catch up with the winds (and vice versa). That is why Katrina's surge was so incredibly large despite the fact it was only a Category 3.

it seems as if Chris and I are trying to explain, but the point is not coming acros clearly.

Model simulations have demonstrated that is fundamentally not true. It is the extent of the hurricane force winds that is the primary cause of surge. A large low end 3, like Katrina, will produce a significantly higher surge than a steady state Charley sized cat 4 every single time

[Lindaloo]

Well I just do not believe Katrina was a low end Cat 3 either. Guess we will have to wait 10 years like they did with Andrew to really know the truth.

[Normandy]

Linda,

I am currently living in Andrew's cat 3 zone... damage was minimal in South Miami. I was only in the cat 4 and 5 zone that we saw the damage

I did a research project for an undergrad history class on this very topic. The findings of poor construction were based upon the belief at the time that Andrew was a category 4 hurricane. Comparisions were made with Donna, which after the reanalysis remained a cat 4. The claim that Andrew's damage was due to poor construction was made by comparing Andrew's damage with Donna's. Of course Andrew's was worse, which, after we had the reanalysis, we now have the reason for it. Andrew's winds were at least 25KT HIGHER than Donna. The difference between 145 and 120KT winds is a factor of 1.46. (145^2/120^2). That is Andrew's force compared to Donna's. Nearly 50 percent more destructive power in Andrew; thus, I am not surprised at the findings of the criminal probe (Operationally, Andrew and Donna had EQUAL landfall winds)

Where did I say anything about the miniswirls not wiping out everything? I said those were Xenia tornados, so of course they wiped out everything and were what caused the damage, against casting serious doubt on the poor construction theory (unless Xenia had construction just as bad, but that would not explain the re-enforced concrete structures)

All I can say about Andrew is that I am glad I was not in Miami then. Wilma was bad enough and it took a while to get over the initial scenes when I finally left the Rickenbacker Causeway that Monday afternoon

Soo by your comment i gather this when comparing WIlma and Andrew in Miami proper.... Wilma caused more damage, yet Andrew produced higher winds in your area in Miami?

Im confused, because if Wilma brought 80-90 mph sustained winds into area, and Andrew brought 115 mph winds into your area, then what happened in Andrew should have far exceeded what happened in Wilma, correct?

And one more question, do u agree with the final analysis of Andrew having 145 kt winds? And were these top winds taking into account the "mini-swirls" or just taking into account the top 1-min sustained wind? Just curious, because clearly Andrew was a freak of nature when it came to wind (it produced 100 kt winds for 30+ mins overland at the turkey power point plant).

[Derek Ortt]

Andrew brought higher winds to SOUTH MIAMI

Wilma brought higher winds to the CITY OF MIAMI

They are two separate cities separated by Coral Galbes

As for the 145KT in the best track, that is the consensus. HRDs HWIND has 153KT at landfall (which I tend to agree with because the 145KT was based upon flight level winds 1 hour before landfall, and Andrew's pressure was falling much faster than Wilma's in the Caribbean during that final hour... fell 10 mb in just 45 minutes and 4mb between hitting the barrier island and the mainland. Thank God it hit when it did or it would have been even worse). However, others, such as Dr Mark Powell are convinced Andrew was a 4 as he believes that shaoling of the waves creates a higher reduction factor at the coast

[docjoe]

Andrew brought higher winds to SOUTH MIAMI

Wilma brought higher winds to the CITY OF MIAMI

They are two separate cities separated by Coral Galbes

As for the 145KT in the best track, that is the consensus. HRDs HWIND has 153KT at landfall (which I tend to agree with because the 145KT was based upon flight level winds 1 hour before landfall, and Andrew's pressure was falling much faster than Wilma's in the Caribbean during that final hour... fell 10 mb in just 45 minutes and 4mb between hitting the barrier island and the mainland. Thank God it hit when it did or it would have been even worse). However, others, such as Dr Mark Powell are convinced Andrew was a 4 as he believes that shaoling of the waves creates a higher reduction factor at the coast

Could you elaborate on the rapid pressure drop just before landfall. I try to read as much as I can from a laymans perspective on canes but I have missed that. I knew Andrew was strengthening but I had no idea that Andrew was deepening that rapidly. Absolutely amazing to me. thanks!!

docjoe

[Derek Ortt]

on Andrew's pressure drop

The final recon fix at 0810 UTC found a pressure of 932mb (this is when the 162KT flight level wind was found)

When Andrew crossed the barrier islands at 0845 UTC, the presure had fallen to 926mb

When Andrew made landfall just east of Homestead at 0905 UTC, the pressure was down to 922mb

[jasons2k]

THE WORST CASE IS THE UNEXPECTED. ALWAYS EXPECTED THE UNEXPECTED TO OCCUR TO AVOID THIS WORST CASE

Hey Derek,

I agree with your statement, history has shown us that the unexpected results in the worst case. However, as a point of contention, I'd point out that Katrina taught is that in some cases, all the warning in the world still won't matter. People quickly forget how dangerous nature can be.

[Normandy]

on Andrew's pressure drop

The final recon fix at 0810 UTC found a pressure of 932mb (this is when the 162KT flight level wind was found)

When Andrew crossed the barrier islands at 0845 UTC, the presure had fallen to 926mb

When Andrew made landfall just east of Homestead at 0905 UTC, the pressure was down to 922mb

So Andrew was really a Cat 5 when Recon measured the 932 pressure...the 90% reduction makes the surface winds 146 kts, which is 165 mph correct? Therefore if Andrew continually stregthened, wouldnt that mean the winds might have been even higher at landfall?