Lessons from Frances and Ivan

[Derek Ortt]

Overall Lesson: It does not take a cta 4 or 5 storm to cause billions in damage. Even a cat 1-2 winds can destroy nearly everything in their path

Now for Frances: A large, slow moving storm 1 cat weaker than a faster moving, smaller storm can cause more damage. Frances caused about 2.5 more than Jeanne

Ivan: Small changes in location make all of the difference. Opal was nearly identical in intensity to Ivan, yet because it passed just east of Pensacola, Pensacola was spared. Ivan went 30 miles west and parts were leveled. Cat 1 winds in a major city will cause severe destruction for that city. Opal 30 miles to the west and Oct 4 would be remembered as the day in which Pensacola was leveled.

[Rainband]

Good points, but "leveled" is a relative term to those that lost their lives and livelyhood that day.

[TheShrimper]

Derek I do not know if you have ever been over here to SW Fla, mainly speaking Pine Island/ Cape Coral area. Norther PI, Bokeelia caught the eastern wall after crossing PI Sound enroute to Char. Harbor. What is underestimated in my opinion after looking at the damages comparatively in certain locations is the fact that tornadic activity in the bands causes the most physical damage incurred. There are old cracker house here built in the same time period, often times by the same builder in a relativly close proximaty to each other. Now when one structure during Charley escapes unscathed from the force and another is leveled 200 yards down the road, one would only infer that sustained HFW would have had the same effect on both structures, but they did not. Likewise in Cape Coral, a city where they cleared all vegitation before developing it, homes facing the south with screen enclosures in the rear suffered minimal damage to the front of the structure and screens remained intact in the northerly facing enclosures. Yet, only a half a mile away, a stones throw so to speak, the frontal amenities to the dwelling were severly damged and the "protected" lanai's in the back of the house were "no more". Same thing vegitation wise. Strands of Australian Pines with 3 ft. diameter bases were snapped off 10 ft. above the ground, where as others not far away, were just stripped of thier needles. some of those that fell victim to the winds seemed to be twisted, not responding to the way they should have fallen in light of the storms track. It definately did not resemble S. Dade in 92 where everything south of Homestead in Florida City was sheared to the east and in the Redlands north, those Australians were toppled westerly. I am a firm believer, that alot of the damages are caused by tornadoes contained in the overall structure of landfalling hurricanes, even if they are undetectable. Or are the detectable with the radar sophistication we have? Just curious.

[weatherwindow]

the presence of tornadic elements within the eyewalls of intense storms are well documented....these are not the very common rainband tornadoes which are frequent in landfalling storms.. these very small vortices appear to spin up in associated with cells of very intense eyewall convection. the exceptional updrafts/downdrafts in this convection seem to sustain and/or accelerate the rotation. andrew, in fact, had just such a vortex which rotated around the eyewall at landfall. the infamous country walk devastation was attributed to exactly that. these vortices are normally pretty short term phenomena. however, this cell was clearly depicted on doppler and infrared. further, dr fujita, when doing his survey of damage, identified swaths of damage associated with the "mesovortices". they were on the scale of a football field. the rotational speed is in the range of 35-45kts(low end F0). this rotational speed is added(when in sync) to the sustained winds of the hurricane. sooo....the damage swaths resulted from the 35kts of the mesovortex added to the 145kts of andrew for very localized swaths of 180kts. although i dont believe this can be verified, i would guess that many cases of exceptional damage in historical storms can be linked with this phenomenon. .....hope i shed some light on it........rich

[Derek Ortt]

That aspect described in the last post may be what caused the damage. The patterns are very similar, if not identical to tornadoes. I am not sure if they can be classified as tornadoes though, but whatever they are, they sure are as strong as a strong F3 to weak F4 tornado.

The damage patterns you described, Shrimper, do not surprise me at all. While I have not been to the area, people from my office have and in the areas of damage, there was complete damage

[Derek Ortt]

Just to further the last post,

it is possible that one of these could have occurred in Ivan as well. Add 35 m.p.h. to 120 m.p.h. winds and you have a nice little F-3 tornado plowing through a region

[Aslkahuna]

These wind streak damage swaths were officially well documented in the Corpus Christi area after they were slammed by Celia in 1970-like Charley, Celia underwent strong intensification just before landfall (and like Andrew as well-might be a hint there as to the processes involved).

Steve

[AussieMark]

These wind streak damage swaths were officially well documented in the Corpus Christi area after they were slammed by Celia in 1970-like Charley, Celia underwent strong intensification just before landfall (and like Andrew as well-might be a hint there as to the processes involved).

Steve

Some parts of the Celia report are as follows

The highly damaging gusts in Celia provided streaky damage. Viewed from a helicopter, a succession of long streaks of heavy damage were apparent as small packets of high energy winds radially spaced from north to south at intervals of a mile or more and raked across the City from west to east. In discussion with town's people and airport personnel these bursts of high energy wind occurred all across the City apparently within the space of about 15 minutes

There was no evidence of rotary motion in any of the areas of the heavy damage. However, long streaks of debris lines were visible from the air extending for hundreds of yards from the structures which were reptured by the gust-velocities. In the City of Corpus Christi these streaks were invariably from a westerly direction. In Port Aransas and Aransas Pass the streaks were from the south to the southeast predominately. In Rockport, Taft, and Sinton there were fewer streaks in evidence and those were visible varied in direction, but none indicated rotary motion as from a tornado.