Katrina H-Wind Analysis, marginal 3 at landfall

[MGC]

In the end it really don't matter what cat the NHC tags Katrina with. With over 1100+ people dead and damage estimates of over 200 Billion, Katrina passed up all the Cat-5 combined that hit the USA in both death and damage. I pray that another hurricane like Katrina never hits anywhere again......MGC

[f5]

in a true cat 5, like Andrew, the wind itself can obliterate anything. Homestead was totally leveled nearly to the extent of the Mississippi Coast due to the wind. In a true strong 4, like Charley, a very similar fate befalls the ladfall zone. Remember, that is a prolonged strong F2 or F3 tornado. IN Katrina, what we had according to the H-Wind analysis is a prolonged F-1 tornado, still VERY devastating on its own, just not quite as devastating as an Andew, Charley, or Iniki from a wind standpoint

If Andrew was a true CAT why did it take the NHC 10 yrs to upgrade him to a CAT 5.The NHC told Homstead resident not to poo poo a lesser storm beacuse the winds in Andrew were mainly CAT 4 140-150MPH(Charley Strength)?The CAT 5 winds revised later were over there on the coast where the burger king is

[hurricanesurvivor]

We stayed in our home here in Picayune and about 10 am the winds changed from large gusts to a steady rumble, which lasted for about 45 minutes, then suddenly died off as we entered the eye. The walls shook, the ground shook, and we were afraid the house we were in (a brick structure on a slab) would not stand. My question is, was the rumble from the sound of sustained wind, or from tornadoes?

[SamSagnella]

I would say that the rumble was due eyewall winds, as any tropical cyclone tornadoes (or pretty much all tornadoes for that matter) would last SIGNIFICANTLY less than 45 minutes in any given location. 45 minutes in the eyewall of a hurricane moving at ~15 mph seems like a pretty reasonable explanation to me.

[THead]

We stayed in our home here in Picayune and about 10 am the winds changed from large gusts to a steady rumble, which lasted for about 45 minutes, then suddenly died off as we entered the eye. The walls shook, the ground shook, and we were afraid the house we were in (a brick structure on a slab) would not stand. My question is, was the rumble from the sound of sustained wind, or from tornadoes?

Sounds like hell. Personal question....would you stay if you had to do it again? Just curious, I'm not judgemental or anything like that, just would like to know. I'm glad you made it through ok. You've been around a couple of months, but belated welcome to Storm 2k!

[quandary]

As I've posted in another thread...

A 918 mb storm will do 918 mb damage.

However you debate it, I believe that the NHC will only move Katrina's winds at landfall up or down 5 mph. The bottom line is that Kat was a Cat 4 at landfall in LA and a strong Cat 3 at landfall in MS.

Huh?? A 918 mb storm will do 918 mb damage?

So a 1004 mb storm will have the same winds regardless of structure or surrounding pressures? Doesn't make sense, because we all know that at different mb's storms have been lower and weaker than others and so on.

???

I meant that a hurricane with a 918 mb pressure, regardless of its winds (trust me, they won't be of Cat 2 strength or lower), will do what you would expect a 918 mb hurricane (marginal Cat 5) would do, even if it is not a Cat 5. Likewise, a hurricane with 980 mb pressure you should expect strong Cat 1 damage regardless of wind speeds.

This is meant as a general rule of thumb. If a hurricane stalls and causes flash flooding the intensity does not matter. But otherwise it works well.

A 918 mb hurricane with 130 mph winds will do exactly 130 mph in damage. Pressure doesn't cause trees to uproot, shingles to fly off, debris to strike windows, or the vast majority of the storm surge. Wind and windfields are all that matter.

I don't think this is accurate. A 918mb storm will do damage like other 918mb storms, not more like storms of similar windspeeds. This does assume a "flat world," as in we are not passing directly over any city areas.

A 918mb storm with 130mph winds will have multiple wind maxima and a large eye, so you get Cat 3 winds over a radius of 80miles versus a 170mph storm with winds over only 15 miles. Of course, if those winds are centered directly over Tampa, the smaller, faster storm will do more damage, but over a range of coastline, both will do the same amount of damage.

The larger storm will likely push a larger surge too, although too many factors such as speed and angle and coastline topography affect this.

[hurricanesurvivor]

No, we definitely wouldn't stay again. We've been through Camille, Elena, Georges, etc. but this was by far worse than any of those! I don't remember being afraid for our lives before.

Another strange thing that happened... right before the rumble began, there were three huge claps of thunder. All five of us jumped it was so loud. I've never experienced thunder during a hurricane before. After the last clap of thunder, it seemed to just keep rolling, which then turned into the loud rumble. Anyone like to hazard a guess as to what that was?

[quandary]

The case about 1004mb storms is not analogous. In a 1004 mb storm, environmental pressure makes a big percentage difference. 1004 is 9mb off the standard pressure of 1013, so if the enviromental pressure is off by 5mb, the gradient is cut in half. Also, if the gradient is loose, the winds are reduced to nothing more than a breeze, which does little or no damage.

When the pressure is very low, say below 960, the difference is going to be on average 55mb. If the environmental pressure is off by 5mb, the percentage difference is going to less than 10%. So the difference is minimal.

By the time we get down to 918mb, where the pressure difference is nearly 100mb, the percent difference induced by environmental pressure disparities is going to be less than 5% no matter what. So you get winds of 140 instead of 147, big deal.

[timNms]

We stayed in our home here in Picayune and about 10 am the winds changed from large gusts to a steady rumble, which lasted for about 45 minutes, then suddenly died off as we entered the eye. The walls shook, the ground shook, and we were afraid the house we were in (a brick structure on a slab) would not stand. My question is, was the rumble from the sound of sustained wind, or from tornadoes?

I remember the "rumble" very well! I also remember the ground shaking, then the house vibrating and shaking. It was an experience like I'd never had before. I also questioned whether I'd have a house after the storm or not. That had to be the longest 45 mins I've ever spent!

[timNms]

Unfortunately, this debate will go on and on. However, one only needs to pay a visit to Waveland, MS to understand what really happened. Say what you will about wind speed, but this thing was nothing less than a cat 5. The destruction along Beach Blvd. and 3 or 4 blocks inland is total and missed nothing. Even the railroad tracks are in shambles.
My wife, daughter, son, daughter's ex fiance and I went down yesterday to rummage thru what was left of his parents' home on the beach. While driving down Interstate 59 through Pearl River County, I was amazed to see the damage. Most of what I saw was tree damage because there are no houses built along the interstate. However, there was one particular area in which almost all of the trees were downed. At the time, I thought that was bad. It was nothing compared to what I was to see.
As we began to enter Waveland, I was taken aback by the cars that were lined up along the side of the road. It didn't take long for me to realize that they were there because the surge had lined them up! Then I began to see houses that had been washed from their foundations and planted along the sides of the road. Most homes north of the track remained standing, but many only had roofs left. Then we got to the tracks. On the north side of the tracks, there were some homes that appeared to be untouched, until one got a closer look. While the outsides looked "ok" the interiors were gutted. Water had left it's mark in the structures. Many of them had been completely submerged by the storm surge (probably one of the main reasons there was not complete roof failures as was seen in Andrew...would be hard for the wind to blow the roof off if it was covered by water, right?) The trees were dead from the salt water. I'm not talking a few feet up the trees. I am talking the entire trees, from top to bottom were dead. Now, had I not seen pictures of the trees beforehand, I would have guessed that the salt water killed the trees from root level. BUT, I'd seen the pictures that were taken shortly after the storm and knew that the tree tops were dead long before my visit. Another indicator of just how high the water level was.
Once we made our way to the tracks and saw the damage, I was thinking maybe it wasn't as bad as I'd been told. Then we climbed the hill and topped the tracks. For as far as the eye could see, there was NOTHING but rubble. There were no houses left. There may have been a few roofs lying on the ground from houses that had been demolished, but there were no structures standing. THis was 3 or 4 blocks from the beach! Yet nothing was left. The sight reminded me of a huge garbage dump. The only thing one could see that let you know houses once stood were pilings that had somehow survived. It was an odd site to see.
Once we finally made our way down to Beach Blvd. and got to Patrick's parent's home, I was awestruck. His parents' home had once been such a beautiful place. Now there is nothing left save the concrete slab, about 10 pilings, and some hurricane straps dangling from them. My wife found a few coins lying buried in the sand near the foundation of their home. There is nothing there that even resembles what was once their house. It had been covered in yellow vinyl siding. None of it can be found anywhere. There were a few dishes lying around the side of the foundation. Out of 3 huge trees that once stood by the house, only one remains lying on the ground. The other 2 were pulled from the ground, leaving gaping holes. No one knows where they are now, tho. Behind their house there was a big tree. Near the top of that tree, there is a palm tree wedged into its branches.
My mind couldn't comprehend all of the destruction. To say there is nothing left of that area does not seem to do justice to what it really looks like. The only way to get a true feeling of what really happened is to see for yourself. Until you've been there, you really have no idea what it looks like. Pictures shown on television do not do justice to the reality of the damage.
Patrick told us of how horrifying it was at the hotel. He said had someone not come along in boats and rescued them, they'd have drowned. He said water was up to their necks by the time the boats came and lifted them to the second floor. He tells of a horrifying story of a young lady and her infant that was brought to the hotel in one of the rescue boats. She was found clinging to the top of a tree. Bruised, cut, beaten and battered by the wind, she was fortunate to have survived!
Again I'll say call it what you want. I've seen the damage first hand and I tell you without a shadow of a doubt, Katrina was nothing less than a catagory 5 storm. Wind wise, there will always be an argument about how "strong" she was. But when you see firsthand what she did to the Mississippi Gulf Coast, you'll have no doubt that she was a monster!

[Matt-hurricanewatcher]

Did this come close to the December Tsunumi. It sure sounds like it gave that a run for its money. Katrina was one bad hurricane. She was a very big storm which helped formed a storm surge bigger then any hurricane ever. Rita the youger sister did some damage. But Katrina to non-western LA/Eastern Texas people will be the one remembered for this year.

[Normandy]

Did this come close to the December Tsunumi. It sure sounds like it gave that a run for its money. Katrina was one bad hurricane. She was a very big storm which helped formed a storm surge bigger then any hurricane ever. Rita the youger sister did some damage. But Katrina to non-western LA/Eastern Texas people will be the one remembered for this year.

Rita is seriously overlooked on these boards (not sayin u are overlookin)....
That hurricane produced the worst damage picture I have ever seen from a hurricane (Holly Beach near Cameron). Rita did tons of damage, and had she moved into Galveston she would have rivaled Katrina (shudders to thonk of Galveston island looking like Holly Beach).

[oneness]

Another strange thing that happened... right before the rumble began, there were three huge claps of thunder. All five of us jumped it was so loud. I've never experienced thunder during a hurricane before. After the last clap of thunder, it seemed to just keep rolling, which then turned into the loud rumble. Anyone like to hazard a guess as to what that was?

I've experienced something related on two occasions.

Once within the core of a very large and slow-moving cat 4 eye-wall and a second time within a fairly mediocre cat 2. The 925 MB cat 4 made landfall directly over a major iron ore province, so I put this extraordinarily vigorous lightning activity down to excess conductivity of the soil and rocks in the area which are about 60% iron oxide by volume. Intense lightning occurred for hours in the core, though the wind was far too loud to hear any thunder.

In the Cat 2’s case the lightning and thunder were much more frightening. At ~1:30 AM the core bands were still about 2 to 3 nm off-shore, on radar. Thus far we had only been having moderate TS winds, little gustiness, and a very fine mist of tiny water droplets had been falling sideways for hours. No lightning at all. So, I'm looking out the windows thinking the storm is a bit of a non-event. Then there's this incredibly bright flash of light. I’m completely dazzled by it and could not see at all for ~10 seconds. However, I immediately realised it must be lightning, so I'm counting to estimate how far away it is, via the time to the thunder report.

I’m thinking it’ll be from a cell very close to shore so after 10 sec I’m surprised … nothing … I got up to about 40 sec … but still no thunder ... confused, I stopped counting ... why no thunder? ... what gives! The lightning had been staggeringly bright, but no thunder! Then, about a minute after the flash, the loudest, deepest most booming and rumbling thunder I’ve ever heard begins. It went on without tapering-off in sound intensity for more than 30 seconds! It was very scary and was totally awe-struck by it … to realise the distances implied and the scale of the discharge required to produce that blinding flash.

Then, almost immediately as the thunder roll finally stopped the winds came onshore with an initial gust which knocked down three of my trees and the two power poles in front of my home. The combined surprise effect of lightning, then impossible thunder, then wind jumping from ~20 knots to a howling shrieking was unnerving. This storm was clearly much more vigorous than I thought. There were two more mega-discharges over the next couple of minutes, but not quite as overwhelming as this first discharge, then no more for the rest of the storm. The next 30 minute warning update on the radio upgraded the storm from cat 1 to cat 2 from radar data as it approached. It made landfall about 4 hours later. I took the extreme lightning discharge to be symptomatic of sudden convective growth in the core as it moved over warmer shelf waters. I expect the length and loudness of the thunder was due to a simultaneous cell-network discharge occurring over much of the core's area.

[Derek Ortt]

NHC took long to upgrade as they used the wrong reduction factor.

Storms in that period tended to be underestimated, even Hugo seems to have been slightly more intense than listed

[mtm4319]

NHC took long to upgrade as they used the wrong reduction factor.

Storms in that period tended to be underestimated, even Hugo seems to have been slightly more intense than listed

To which storm are you referring here (if you're talking about the cat 2 that oneness described in his post immediately above yours)?

[frederic79]

One thing I remember about Elena in 1985. The lowest pressure recorded at landfall by recon was 959 mb and 953 at Pascagoula. The strange thing is Elena was ALSO said to be a Catagory 3/125 mph hurricane at landfall. That's supposedly the same windspeed as Katrina but with a 953 mb pressure compared to Katrina's 923 mb. A whopping 30 mb difference and as bad as Elena was, there is no comparison to Katrina - NONE. Consider that Elena's eye passed directly over my area, Pascagoula, and Katrina's eye was a full 60-65 nm to the west. Pascagoula was devastated. There was tremendous wind as well as water here. Therefore, I cannot believe Katrina's core winds were only 125 mph in Waveland. That doesn't add up. And what causes and MAINTAINS a 25-30 ft. surge if not the winds. Yes, Katrina was HUGE but also extremely intense and integral. I'm convinced the strongest winds were missed by recon at landfall and research will bear this out in time.

[WeatherEmperor]

Maybe we will never truly know. I suppose this is why weather is and forever will be an inexact science.

<RICKY>

[jasons2k]

NHC took long to upgrade as they used the wrong reduction factor.

Storms in that period tended to be underestimated, even Hugo seems to have been slightly more intense than listed

To which storm are you referring here (if you're talking about the cat 2 that oneness described in his post immediately above yours)?

Derek is referring to Andrew in response to f5.

[Anonymous]

NHC took long to upgrade as they used the wrong reduction factor.

Storms in that period tended to be underestimated, even Hugo seems to have been slightly more intense than listed

I heard Hugo's landfall has been bumped up from 135 mph to 140 mph

[Derek Ortt]

Elena also came in at a 10 degree angle, which means very little tidal surge, while Katrina came in an a perpindicular angle, which resulted in the maximum surge

the angle of impact is VERY important for the tidal surge heights