(*Chip Merlin’s Note–Rocco Calaci has been a noted meteorology expert witness in the Katrina Legal Wars. After meeting him at a recent FAPIA Convention, I invited him to write a series of guest blogs. Click here to read his previous guest blogs)
Whenever a hurricane strikes a community, we obsess over the maximum wind speed and storm surge depth. In my last blog, I mentioned many other weather elements within a hurricane that can cause damages. Now I want to speak my mind on how we need to look at hurricane damage from another perspective.
Many people have heard of Dr. Theodore Fujita, the developer of the renowned Fujita Scale used to categorize tornadoes by intensity. The first Fujita Scale was presented in 1971, two years after the Saffir-Simpson Scale was released to the public. One of Dr. Fujita’s goals was to make the Fujita Scale a smooth transition from the Beaufort Wind Scale. Fujita explained explicitly that "F-scale winds are estimated from structural and/or tree damage, the estimated wind speed applies to the height of the apparent damage above the ground."
This means that the Fujita Scale only applies at the height of damage, whether it is 8 feet above the ground or 40 feet above the ground. There is nothing in Dr. Fujita’s definition that states the winds have to be measured precisely at 33 feet above the ground, yet some experts use wind measurements from many miles away recorded at 33 feet to substantiate their “opinions.”
Anyone who thinks that wind speeds measured at one location can be applied to other locations doesn’t understand the atmosphere. The atmosphere is made up of wind bands that flow up and down easily, causing wind speed increases and decreases that are not seen or measured, but we know they exist by observing how these winds affect objects around us.
I am constantly amazed by those who assert that we MUST use wind speeds recorded at some location 30 miles away because that is the only location where official measurements are made. That is pure bunk.
Using that logic is like telling a police officer the reason you were doing 70 miles per hour on a back road is because the speed limit is 70 miles per hour 30 miles away. Would a police officer buy that excuse? It never worked for me.
Let’s all use realistic scenarios; not studies that were performed many years ago in another part of the country. Let’s compare apples to apples.
With that being said, Dr. Fujita devised his scale based upon a 3 second gust; not the sustained 1 minute wind speed. The Enhanced Fujita Scale is based on the same 3 second gust principle.
To me, this means that Dr. Fujita clearly understood the force of wind and the impact of wind force. If a 3 second gust can cause all types of damage in one occurrence, how much damage can be experienced if there are multiple gusts?
According to Dr. Fujita’s Enhanced F Scale Damage Indicators, the “expected wind speed” to cause the uplifting of a roof deck, loss of more than 20% of roof covering material, the collapse of a chimney at a 1 or 2 story residence is only 97 miles per hour. The lowest boundary for this type of damage is only 81 miles per hour. If a 3 second gust can cause this level of damage, what happens in a hurricane with continuous gusts? What happens with hurricanes that have continuous wind speeds at or above the “expected wind speed” for any type of structure?
The following is taken from the Storm Prediction Center website for The Enhanced Fujita Scale:
Over the years, the F-Scale has revealed the following weaknesses:
- It is subjective based solely on the damage caused by a tornado
- No recognition in difference in construction
- Difficult to apply with no damage indicators
- if the 3/4-mile wide tornado does not hit any structures, what F-scale should be assigned?
- Subject to bias
- Based on the worst damage (even if it is one building or house)
- Overestimates wind speeds greater than F3
And the F-Scale has had its misuses over the years:
- Too much reliance on the estimated wind speeds
- Oversimplification of the damage description
- Judge the F-scale by the appearance of the tornado cloud
- Unrecognizing weak structures
- mobile homes
- modified homes
The meteorological and engineering communities recognized these weaknesses and took steps to improve the original Fujita Scale. In 2006, a panel of selected experts devised an Enhanced Fujita Scale, which was accepted by the National Weather Service.
The new EF Scale lowered the wind speed ranges necessary to cause damage to a variety of structures and added a more refining step to the evaluation process by breaking out each type of structure with degrees of damage (DOD). I believe this addition is great because it is more realistic. One of the main weaknesses of the original Fujita Scale was that it thought of all structures as equal. The EF Scale, with its’ DOD indicators, is a wonderful improvement to the Fujita Scale.
I question why some of the panel members of the Enhanced Fujita Scale project ignore their own recommendations when assessing damages from a hurricane?
How can anyone apply guidelines from the Great Plains to hurricanes along the Gulf Coast? This is comparing apples to elephants.
For both Hurricane Katrina (2005) and Hurricane Ike (2008), some experts state emphatically that there were no tornadoes along the coastline. Published studies from the National Weather Service and National Hurricane Center clearly state that there are tornadoes in each and every land-falling hurricane, including the coastline. Why the disconnect?
Just because a person has a lot of knowledge about tornadoes in Canada, is he an expert about tornadoes anywhere in the world? Does this mean that everything that applies to Canadian storms also applies equally to the Gulf Coast? I don’t think so.
That is like someone from Canada coming to the Gulf Coast and trying to “shovel” all our rain…it doesn’t work.
Many people will emphatically argue that the EF Scale and the original scale pertain only to tornadoes. Yes, tornadoes are a complete vortex with tremendous upward vertical motion which embellishes the interior wind speeds of a tornado. People tell me that it is the constant rotation and rate of change in shear and wind speed of a tornado that is so critical in causing damage.
The wind field of a hurricane is inherently rotational. The rate of change in wind speed and shear of a tornado can be found within several weather elements of a hurricane. The National Center for Atmospheric Research and NOAA state “hurricane tornadoes are more frequent than classic Midwest tornadoes because there is more rotation in the hurricane environment to draw upon.”
A tornado is a relatively short-lived phenomenon when compared to most other weather elements. The majority of time when tornadoes occur, they contain the highest wind speeds of the surrounding atmospheric environment on the surface. The rate of change of wind speed and rotation (shear) between the surrounding atmospheric environment and the tornado is tremendous, yet Dr. Fujita never mentioned that a specific rate of change in wind speed and shear were necessary to cause the listed damages. All Dr. Fujita listed were wind speeds.
With the Enhanced Fujita Scale, the panel members gave specific speed ranges to a variety of structures, each with 10 separate degrees of damage. The EF Scale is very detailed and thorough.
My question is if Dr. Fujita and the members of the Enhanced Fujita Scale project believe that a 3 second gust of 97 miles an hour will cause considerable damage to a 2 story residence, why can’t hours and hours of wind gusts equal to 95 miles an hour result in more damage?
It seems that people miss the point that structures are enduring hours and hours of punishing wind speeds and associated elements. If a 3 second gust can collapse a chimney, why wouldn’t the winds that enter the house after this specific damage be considered factors in the damage?
If a 97 mile s per hour gust can cause the uplifting of a roof deck, what happens when that 97 miles per hour gust occurs repeatedly for several hours? A gust of only 121 miles per hour will shift a 1 or 2 story residence off its foundation. What if gusts this high occur numerous times over several hours along with high winds in between each gust to 121 miles per hour? If wind gusts to 96 miles per hour cause glass breakage in windows and doors, why don’t we consider what happens once the winds enter the house and cause damage on the inside?
We need to stop focusing only on the maximum 3 second gust. We should be looking at how continuous hours of wind pummeling affects any structure. A good heavyweight boxer can knock you out with one punch, but a good lightweight boxer can do more damage to you after hours of punching. Either way, you lose the fight.
So I ask, why do we focus on the highest wind gust and surge depth, when lesser winds can cause as much or more damage? Maybe we should be using a different ruler.