new ivan landfall info... no cat 4

[Sanibel]

Ah, an important thing not mentioned above is the ramming effect of geography. The way Ivan came into Pensacola accentuated his surge by forcing it up the bay and river like they were fearing over in Mobile. Not very difficult to figure out. If a category 2 storm piles surge into a confined bay in a prolonged landfall the way water dynamics works is that the piled water will have more piled water go over the top of it as it is forced landward by winds. In this case it is very reasonable that a 12-14 foot surge could register as 20-25 feet in certain places susceptible to this ramming effect.

I do recall someone claiming the wind records at landfall were not that high...

[Derek Ortt]

max storm surge heights were about 12-14 feet. This DOES NOT INCLUDE BREAKING WAVES. These waves are on top of the surge; thus, the water marks will likely be somewhat higher as these waves were about 30 feet higher than the surge was. What also made this worse was that it hit at a 90 degree angle, while Opal was about 60 degrees, reducing that surge somewhat (though it was still about 10-15 feet in isolated, unpopulated areas

[Derek Ortt]

Had Pensacola have made landfall in the same place where Ivan did, I'd expect the effects to have been quite similar to those form Ivan. Pensacola not only had strong TS/cat 1 winds from Opal, they also had an offshore wind. In an offshore wind, the barrier islands take all of the ocean side surge as it is only from waves, not wind

[Sanibel]

So I think we have established reasonable grounds for a winding-down major to have sent category 2 winds over Pensacola in a bottleneck effect off the bluffs and up the bay. Ramming bottleneck-concentrated winds combined with waves probably explains the huge surge there. Out on the shore the forward remnant surge from the offshore burst probably came in with the storm as a 'wake' of sorts...

[Droop12]

Ok Derek, I forgot about breaking waves. That could explain why everything is broken into splinters near the water. I did see a few one story house that survived except they were gutted and there was 4 or 5 inches of leaves and pine straw and other odd things accumulated on its roof. That tells me the surge went over its roof, and after the water receded, the debris "sat down" on the roof like it would on the ground. So you think a 12 - 14 ft surge with 30ft waves on top? I did hear city officials say waves were nearing 25-30ft in the sound.

[Droop12]

I agree with your idea Sanibel about the "wake" idea. Still a bit skeptical about the winds though. I honestly dont think I'd be as scared as I was during Ivan if it was a Cat 2. I've never really been scared during any storms like I was in Ivan. I had a video cam. and I planned to tape some of the worst of the storm from the door but when it was sucked open around 12 or 12:30am, and I saw what was happening outside I decided I'd rather not. From then on till sunrise it sounded like hell.

[Opal storm]

Ivan WAS a catagory 3 despite what people think.A catagory 2 is not capable of doing that kind of widespread damage.And I think the NHC knows that,so I don't expect them to increase or decrease the strength of Ivan.IF they do downgrade Ivan,they might as well downgrade Charley too becuase I really saw no difference in the two (damage wise).

[Derek Ortt]

12 to 14 feet wiht 30 foot waves would be about correct. This is consistent with a marginal to moderate 3 in the area.

what I would like to see happen is further education in that making people aware that their particular location in a typical cat 1 or cat 2 will not see hurricane force winds and that only the right front eye wall of a 3 receives cat 3 winds. areas on the other side receive strong cat 1, unless there is shear like in opal, which would result in the effects being quite less. This education is not made on a large enough scale and those experiencing the weak side of these storms think that they endured the worst.

Opal storm, you must not have much of a physics background. Water is much more dense than is air; thus, is much more capable of producing significant damage than is wind. Charley was a wind storm, while Ivan was a water storm. Thus, individual buildings on the coast will resemble punta gorda, which was damaged by wind

[MGC]

Here is my two cents....I have not yet made it over to Pensacola. However, I've looked a many a picture of Ivan's damage. I've witnessed first hand the damage cause by the following major hurricanes. Betsy, Camile, Fredrick. IMO, Ivan's damage was just a bad as Fredrick, more than Betsy and much less than Camile. I feel confident that Ivan was a Cat 3 at landfall. Only a strong Cat 1 or Cat 2 in Pensacola? Perhaps in small sections that didn't get the eye wall. From what I can gather, the wind field in a hurricane is not linear in relation to distance displaced from the eye. I suspect the wind field is simular to a large multi-vortex tornado. With the wind field becoming turbulent over land, some areas will experience much stronger winds only a short distance removed due to the rapid mixing of the wind due to friction.....MGC

[hurricanetrack]

Here's what I know as fact:

My instruments on Gulf Shores- at the beach-front- measured three interesting things-

One: minimum air pressure of 947 millibars in the eye as it passed over my vehicle mounted instruments JUST off the beach at Gulf Shores Police Dept. The vehicle I had placed on the beach was under at least 8 feet of Gulf water.

Two: maximum 1 minute sustained winds at my vehicle on the beach- with a 5 meter anemometer height- was ONLY 89mph around 1:02 am CDT. Here is an excerpt from my data log:

09-16 01:59 47 62 354 355 0
09-16 02:00 69 87 354 355 0
09-16 02:01 76 98 354 355 0
09-16 02:02 89 114 354 355 0
09-16 02:03 69 102 354 355 0
09-16 02:04 72 99 354 355 0
09-16 02:05 70 88 354 355 0
09-16 02:06 68 88 354 355 0
09-16 02:07 77 82 354 355 0
09-16 02:08 66 81 354 355 0
09-16 02:09 79 96 354 355 0
09-16 02:10 68 89 354 355 0

Looking at the first line- it reads: date, time, avg wind, gust, direction and std deviation (direction and std deviation failed).

I was on the north side of any eyewall that was left. I head little in the way of that deep roaring sound- although I did stay close to or inside of the Police Dept to keep safe. I truly believe that within the RFQ- areas in Florida received 115 mph sustained winds even for a few minutes- with gusts to 130 or so. My air pressure of 947 is too low for a cat-2 in any scenario. Heck, Charley's pressure on my vehicle was 943mb and we had winds gusting to 133 mph. So it leads me to believe that the dry air was undercutting the convection starting on the west and south side- working around the circulation- but not in time to prevent cat-3 conditions along the FL panhandle. There they had straight onshore flow during the landfall- with little frictional effects. The wind I measured was coming in from the east-northeast to east (one can figure that out my looking at radar images of rainbands). Therefore, the wind I measured was blowing over land for a little while along its path- thus producing lower winds.

Anyhow- that's my take on it. I was in Gulf Shores and they had a cat-3 pressure with a cat-3 surge- with cat-2 winds at worst. Two out of three wins it for me- it was a category three hurricane at landfall- period. Just not for everyone. Especially people on the west side. That's another story I'm sure.

[Derek Ortt]

that wind reading is a key reading. I am surprised of 89 sustained, I would have though you would have had closer to 95-100.

Of note though: Gloria was at 942mb at Hatteras, but was only a cat 2 with 90KT winds (even that may be generous as Hatteras barely reported cat 1 winds, despite the 942mb pressure reported then)

we likely had more intense winds in W Pensacola, probably in the 95-100KT sustained based upon the flight level recon data

[Droop12]

Derek, Do you think that in the eastern eyewall there could have been small "tornado like" features, I think Dr, Fujita called them sub vortices or basically small tornados that can create streaks of damage such as in Andrew? From what I've seen, I think its possible because the damage pattern was very uneven in some spots. I saw a few house completely destroyed in Pensacola, but the ones directly on either side only had minor damage. I also noticed it with trees...A long streak of trees would be completly snapped but the rest were still standing. Any idea what could cause this? I know Southern Wx probably has some knowledge of this.

[flyingphish]

Those are real deals. Andrew in 92 and Charley in 2004. Fill in the blanks if you wish.

[Sanibel]

I'd like to ask Derek how those second and third story structures above the storm surge sustained category 3-type damage with shattered frames and pushed-in walls? I believe this was non-tornadic due to the lengthy distribution and straight-line look to the damage...


.

[Derek Ortt]

that may very well have happened, as is typical with hurricanes at landfall. These areas usually have the worst of the wind damage and explains the streakiness of the damage. This was also the wind pattern of Fran, another marginal 3 that hit Cape Fear, but produced very similar surge damage as did Ivan

[Derek Ortt]

what it appears from the h-wind analysis is that the hurricane force winds lasted for many hours (8-12), while in Opal, they only lasted for 4 hours. The duration of the winds was very long, producing mroe damage

[jes]

Pensacola was on the East side of Frederick - How severe was their destruction from Frederick. I am in West Mobile and our destruction from Ivan (remember we're West) was quite bad. I had a 30 ft tree uprooted in my back yard. I don't remember any damage from Opal or Erin in Mobile - at least not in my neighborhood. Ivan was a strong storm. It had to have been.

[Derek Ortt]

strongest winds didnt come near pensacola with frederic

[mikey mike]

the category doesn't matter.that's just a statistic.the non-human factor.what matters is the consequences:the casualties,the desruction,the suffering of the victims.to a lot of people a hurricane is just a sat. picture.these things aren't fun.these are deadly storms.these things kill,destroy peoples lives. the category does't matter. if a hurricane detroys someone's home you think they're worried about what category it fit in to? I don't think so.

[tronbunny]

This whole argument just supports my contention that the Saffir-Simpson scale needs an overhaul, or we need a multi-facet scale to make the public more aware to the potential damages.