Help Needed In Assessment of Wind Speed With the EF Scale

[Zachary Gruskin]

Hello all,

I would like an independent analysis of what range of wind speeds would result in the damage in each picture, and an explanation (I have already attempted an analysis but do not want to bias anyone). I will greatly appreciate help, and acknowledge whoever helps me in the paper I am writing.

(Images courtesy of the NWS)

 

[Kiel Ortega]

Great pics! I'm assuming these are tornado pictures...I love small tornadoes...the accelerations are amazing. I surveyed a tornado west of Union City, OK, this past year and at one point the tornadic winds were maybe 10 yards across and then looked to just stop! Anyways, to your pics...

First off, this is really going to be a rough assessment because of the aerial shots...really need to be on the ground for the absolute accurate and best rating. Second, this is just my personal opinion based on 1 year experience doing damage surveys.

Pic #1: Have to wonder about the integrity of the roof since it's completely gone. I don't know what the window situation was on the away side of the house...but if there were large windows blown out there, the walls on the toward side of the house probably didn't stand a chance...same goes for the roof too. Amazing, as it looks like the vegetation around the house hung tight but the power poles are knocked down. The debris didn't go far downstream either. Given all that and not knowing construction quality, I would go weak EF-1 (winds less than 95 mph), the vegetation looks too good to go higher and I wonder on the quality of construction.

Pic #2: Looks to be pretty good vegetation damage with some trunks snapped around the house. Other flattened vegetation to the top-side of the house. Leaning power pole and looks to be an outbuilding that looks to have just collapsed and the debris stayed put. The gas tank rolled is cool (just my opinion). Have to really wonder what was keeping this roof on this house (gravity?). The house held out fine. Given the questionable attachment of the roof, the tree in bottom center that looks to have held fine with other trees beaten up, I would go EF-1 (winds 95-105 mph).

 

[Zachary Gruskin]

Thanks for that great analysis Kiel!

And these pics are aerial surveys after Hurricane Humberto. It appears that mostly everything was straight line wind, and the NWS noted that in their final report. I wouldn't doubt a small tornado here and there though with the odd pattern of damage.

The NWS didn't focus on the house damage in their report, mostly power lines, vegetation, and a gas station, so this info is great for the paper I'm writing. I'm trying to ascertain what the peak gusts were in Humberto (for a small part of the paper at least).

BTW, what is your organization so I can give you proper credit?

 

[Joel Wright]

Amazing that in the top picture the one house is severly damaged, while the other one is completely untouched. Doesn't appear to even be missing a shingle.

There appears to be more of the roof that is not in this picture. If you look closely the amount of material that would make up the roof is far less than the debris we can see in the photo. I would guess other portions of the roof are outside of the frame of the picture.

 

[Doug Lee]

Closer inspection of the first picture brings out some interesting details. The damaged house is between 2 undamaged houses, so we are looking at either a quality of construction issue, or a highly localized strong wind. Also all three houses appear to have the living areas exclusively in their second stories, as if the ground floors are used as a garage and/or storage area. This probably a variation of the houses built on stilts in flood prone or coastal areas. The higher elevation of the roofs might have exposed them to slightly higher wind speeds.

The house in the second picture is single story, so it might not be as close to the flood-prone areas.
Kiel, that gas tank looks to be a propane tank. IIRC, propane tanks are not anchored so they can float. I hear that nasty things happen when propane comes in contact with water. If the tank is allowed to float, that reduces the chance that flood water will overflow the tank and get inside. Do you still think it's cool? (Don't take that as a personal atttack, I'm just asking.) If that thing had blown, we'd be looking at a whole different damage pattern!

I'm not sure how all this affects the EF ratings, but I thought these might be some important details to consider.

 

[Forrest lambert]

just by looking at the pics i wanna say possible EF1 to EF2 tornado!

 

[Greg Higgins]

The most important point to consider is the "quality of construction". There are so many "do-it-yourselfers" that don't have a clue about construction and then there are the "new" construction companies and flyby nighters. Unless you can actually get down and check for the proper attachements (nails, screws, etc) and how they were attached / installed, you will never have a true understanding of what happened. You might contact Tim Marshall as this is his area of expertize. As a side note, the Arlington, TX tornado that occured several years ago was downgraded from a 3 to a 1 (if memory serves) because the damage assessment discovered that the brick veneer was free-standing (the contractor did not use brick ties!) and the garage doors were not installed properly. Folks just trying to make a fast dollar.

Greg Higgins

BTW, first picture, stright line winds, roof was not anchored properly.

 

[Zachary Gruskin]

Thanks for the further responses guys!

And yeah, I agree with you Greg that this probably has ALOT to do with poor construction. You don't lose your roof in a borderline cat 1-2 hurricane with a few isolated gusts to cat 3 unless it was barely on in the first place.