Monday, November 11, 2013

Does the World Need a Category Six For Cyclones

With the disaster in the Philippines wrought by super typhoon Haiyan, once again the unseemly arguments appear about exactly how fast the winds were blowing at landfall and aw gee there were worse storms, the damage to global GDP was minor.  Eli however, and some others have another question.  Would it be useful to reformulate the Saffir-Simpson scale?  Actually two.  Would it also be useful to coordinate the new Saffir-Simpson scale with the Enhanced Fujita scale for tornadoes?

The argument, at least the one the Bunny is making, has nothing to do with climate change, and everything to do with policy, construction codes, public safety and history.  Both the Saffir-Simpson and the Fujita scales were designed for public officials to use in determining how to react to cyclones and tornadoes.  The ranks are set not so much by wind speed and other parameters such as precipitation, as to the expected damage that a storm would do.

Eli will argue that forecasting and construction progress has overtaken the Saffir-Simpson scale and it is time to revise it.  Moreover, while there are few places which are subject to both hurricanes and tornadoes, a uniform scale would prevent the public from perceiving a lesser/stronger danger when warnings are issued.  The Fujita scale itself was revised in 2006 with this in mind by the Wind Science and Engineering Center at Texas Tech

Although the Fujita Scale has been in use for 33 years, the limitations of the scale are well known to the users. The primary limitations are a lack of damage indicators, no account of construction quality and variability, and no definitive correlation between damage and wind speed. These limitations have led to inconsistent rating of tornadoes and, in some cases, an overestimate of tornado wind speeds. Thus, there is a need to revisit the concept of the Fujita scale and to improve and eliminate some of the limitations.

F Number Fastest 1/4-mile (mph) 3 Second Gust (mph) EF Number 3 Second Gust (mph)
0 40-72 45-78 0 65-85
1 73-112 79-117 1 86-110
2 113-157 118-161 2 111-135
3 158-207 162-209 3 136-165
4 208-260 210-261 4 166-200
5 261-318 262-317 5 Over 200

The new scale was built by polling experts on the upper and lower bounds of wind speed that would cause different types of damage to various types of buildings and structures (including trees).  Details, as always, at the link.  The experts then aligned the Enhanced Fujita scale to the old Fujita Scale.

This history is important, because defenders of the Saffir-Simpson scale, including Saffir, claim that there is no need for a category over 5, because at 5, nothing is left.

Eli has seen one reaction from a hurricane forecaster which is typical
CAT 5 is already catastrophic.  What is to be gained by our making a distinction between catastrophe and armageddon?

CAT 5 landfalls are rare, three times in a century for the US. When there is a clear forecast of a CAT 5  hurricane landfall, motivation levels are already so high that additional stimulus is likely to produce a decline in rationality and performance among evacuees. Even if a hurricane were to reach CAT 6 or 7, it would most likely be weakening by the time of landfall. Since the object of the game is to communicate with people in a way that helps them make life saving decisions, we don't want to redefine the SS Scale in a way that exaggerates the hysteresis in public perception that already occurs when a formerly very intense weakening---but now weakening---hurricane approaches landfall.  
Eli begs to differ.  Nothing is left maybe, with the construction techniques of 50 years ago.  Even in favelas, third world shanty towns, there is the occasional masonry building, and especially with roof straps and other techniques, such buildings can be used as shelters from low end Category 5 storms.  With more money, bunnies can hurricane proof their burrows, but when hit with a > 200 mph gust, well. . .

And thus the need

UPDATE:  For a somewhat different POV which reaches the same conclusion see Climate Crocks 

Coby chimes in 


Thomas Lee Elifritz said...

I'm pretty comfortable in my place in the Bahamas for that sort of thing, although I haven't seen anything that big yet. For category six I'd probably want to bolt the window boards straight through the steel reinforced concrete with big stainless steel backing plates, and the roof is still generating a little bit too much lift for my taste. Six inches in 12 feet, lol. The hurricane proof dock took me a while to sort out too.

Aaron said...

We have locked in hundreds of years of increasing ocean heat, so we can expect the intensity of storms to increase - a lot.

We need to push policy makers and managers into accepting this and give engineers the tools for designing to survive such hazards. Part of that is being able to measure and talk about what we face.

We need new storm hazard scales that include wind force, rain, and storm surge.

We need to be thinking about how to build wind-proof bunny burrows that do not flood.

If done with thought, it is not expensive. Look at Hong Kong. They are ready for a 10 meter storm surge. However, NYC was not ready, so Sandy was expensive.

coby said...

A couple of posts I just put up that relate to this. One unintentionally explains WUWT's problem. The issue is the definition of sustained wind speed. WUWT is using a meteorological definition of 10-minute average and comparing it to reports that rely on the tropical cyclone scales which relate to 1-minute average (in general). So yes, this was one of the strongest storms ever to make landfall and headlines to that effect are not exaggerations.

The other also addresses the question "should we go above category 5" (no). I suggest 5A B C etc.

jyyh said...

I'll just note sarcastically that having an open-ended system of measurement in a finite world/universe is a bit unscientific.

Anonymous said...

Speaking of scoring cyclones, I posted at Skeptical Science the comment below, but have not yet had a reply. Perhaps someone here could answer?

"On the matter of Haiyan and the discussion of its strength, can anyone quickly explain if it is possible to compare cyclone energy for different storm events by integrating the physical nature of the wind and pressure surges over space and time? I know that accumulated cyclone energy is usually scored using wind speed as a measure but I'm curious to know how well surge might act as a proxy."

Bernard J.

Cep said...

Meanwhile in Warsaw...

Philippines Negotiator Ties Massive Typhoon to Global Warming and Pledges Hunger Strike at Warsaw Climate Talks

...and in Croatia, yesterday:

A fireman is seen flying on a piece of metal roofing as a bad storm pummels central Europe:

Anonymous said...

extended beaufort scale conversion to a new scale for hurricane-force winds (of above 11,5B) yields values 5,6 (rounded to 6) for land-falling Camille, and ~5,8 (rounded to 6) for land-falling Haiyan which was gusting at 7,1 (230mph).