Saffir-simpson Scale To Be Tweaked...

[Katherine]

Just seen this on the NHC's site:

http://www.nhc.noaa.gov/aboutsshs.shtml

Most significant paragraph I can work out from it is:

Earlier versions of this scale - known as the Saffir-Simpson Hurricane Scale - incorporated central pressure and storm surge as components of the categories. The central pressure was utilized during the 1970s and 1980s as a proxy for the winds as accurate wind speed intensity measurements from aircraft reconnaissance were not routinely available for hurricanes until 1990. Storm surge was also quantified by category in the earliest published versions of the scale dating back to 1972. However, hurricane size (extent of hurricane force winds), local bathymetry (depth of near-shore waters), and topographic forcing can also be important in forecasting storm surge. Moreover, other aspects of hurricanes - such as the system's forward speed and angle to the coast - also impact the storm surge that is produced. For example, the very large Hurricane Ike (with hurricane force winds extending as much as 125 mi from the center) in 2008 made landfall in Texas as a Category 2 hurricane and had peak storm surge values of 15-20 ft. In contrast, tiny Hurricane Charley (with hurricane force winds extending at most 25 mi from the center) struck Florida in 2004 as a Category 4 hurricane and produced a peak storm surge of only 6-7 ft. These storm surge values were substantially outside of the ranges suggested in the original scale. Thus to help reduce public confusion about the impacts associated with the various hurricane categories as well as to provide a more scientifically defensible scale, the storm surge ranges, flooding impact and central pressure statements are being removed from the scale and only peak winds are employed in this revised version - the Saffir-Simpson Hurricane Wind Scale.

Any thoughts?

[Terminal Moraine]

It does seem logical to use only the peak wind speeds to categorise hurricanes because trying to estimate the effect of a large group of variables and then reduce that effect into one, all important, number is fraught with difficulty, as outlined above.

I'm not sure how the majority of the public interpret the Saffir-Simpson scale when they hear/see the numbers quoted, in my own mind I think primarily of wind speed rather than the spatial extent of the hurricane, the size of the storm surge or the intensity of the rainfall.

If the number quoted relates only to wind speed it does give a snapshot indication of the likely amount of devastation from that parameter alone and I'm sure that forecasts local to the likely impact area will go into much greater detail regarding the threat of storm surge or very heavy rainfall.

[Somerset Squall]

Agreed TM. I purely think of the SS scale category as winds alone anyway. Ike last year was a cat 2 at landfall, yet the storm surge was akin to a cat 4- around 20ft. This is the main reason Ike was so devestating to the Gulf coast. I fully support the change of name because the scale only accurately represents wind. Storm surge is often related to the size of the storm, or the angle the storm drifts onshore and the topography of the coastline, not just wind speed.

[ukweathergirl]

I don't ever really remember hearing about the storm surges when they mention the catagory of the hurricanes that hit land just the wind speeds. Is this a contemplation of changing the SS-scale or a definate but just a matter of time?

[butler_son]

Agreed TM. I purely think of the SS scale category as winds alone anyway. Ike last year was a cat 2 at landfall, yet the storm surge was akin to a cat 4- around 20ft. This is the main reason Ike was so devestating to the Gulf coast. I fully support the change of name because the scale only accurately represents wind. Storm surge is often related to the size of the storm, or the angle the storm drifts onshore and the topography of the coastline, not just wind speed.

I'm with you, I've only ever thought of the SS scale to be wind. There are many other factors that surely contribute to storm surge that you'll never come up with a successful scale that includes both wind speeds and surge into one. The only way to do that would be a parallel surge scale, which would just get confusing.

It's not a whole revamp of the scale though, not the big deal they make it out to be. SS, what would your opinion be if the Americans came into line with the rest of the world and used 10 min wind averages? Would this be easier for comparison? Especially in the case of say Hurricane Ioke (I think), which travelled into the West Pacific and was then measured with the 10 min avg rather than the 1 min avg.

[Somerset Squall]

I'm with you, I've only ever thought of the SS scale to be wind. There are many other factors that surely contribute to storm surge that you'll never come up with a successful scale that includes both wind speeds and surge into one. The only way to do that would be a parallel surge scale, which would just get confusing.

It's not a whole revamp of the scale though, not the big deal they make it out to be. SS, what would your opinion be if the Americans came into line with the rest of the world and used 10 min wind averages? Would this be easier for comparison? Especially in the case of say Hurricane Ioke (I think), which travelled into the West Pacific and was then measured with the 10 min avg rather than the 1 min avg.

I rarely pay much attention to the 10-min average. I use the NHC obviously for the East Pacific and Atlantic, and the JTWC for the rest of the basins (who also use 1-min average). To me, a 1-min average is a fair measurement of sustained winds. You don't normally get gusts lasting that long. However, I think the 10-min average is too long. IMO, there is a greater chance of anomolies, and skewing using the 10-min average. What's wrong with 1? It may just be me but I find, for example, calling the monster that was TC Hamish earlier this year a 115kt system (10-min average) to be wrong. The 1-min average was 130kts, and looking at the near perfect structure and very well defined eye this wind measurement seems closer to the mark for me. So I would prefer it if the rest of the world came into line with the Amrericans and use the 1-min average . It would be easier indeed however, if everyone used the same method of measuring sustained windspeed.

Hamish at peak windspeed (115kts- 1-min average, 130kts 10-min average:

[butler_son]

I rarely pay much attention to the 10-min average. I use the NHC obviously for the East Pacific and Atlantic, and the JTWC for the rest of the basins (who also use 1-min average). To me, a 1-min average is a fair measurement of sustained winds. You don't normally get gusts lasting that long. However, I think the 10-min average is too long. IMO, there is a greater chance of anomolies, and skewing using the 10-min average. What's wrong with 1? It may just be me but I find, for example, calling the monster that was TC Hamish earlier this year a 115kt system (10-min average) to be wrong. The 1-min average was 130kts, and looking at the near perfect structure and very well defined eye this wind measurement seems closer to the mark for me. So I would prefer it if the rest of the world came into line with the Amrericans and use the 1-min average . It would be easier indeed however, if everyone used the same method of measuring sustained windspeed.

Hamish at peak windspeed (115kts- 1-min average, 130kts 10-min average:

I think it's one of the main reasons I don't have as much interest in systems in other basins is because of the different scales. If they were all in line (and I could be bothered to use the JTWC) then I might...but all the boundaries are different as a result of the different measurements...aaaargh! Yep, I'd be happier if everyone came on board with the Americans...for once!

Oooh, if I'm picky, surely that could be more symmetrical?

[Somerset Squall]

I think it's one of the main reasons I don't have as much interest in systems in other basins is because of the different scales. If they were all in line (and I could be bothered to use the JTWC) then I might...but all the boundaries are different as a result of the different measurements...aaaargh! Yep, I'd be happier if everyone came on board with the Americans...for once!

Oooh, if I'm picky, surely that could be more symmetrical?

I probably have a bit of a bias- 1-min windspeeds are always higher than 10-min, so it makes it more interesting . It is quite annoying I agree. JTWC are not too bad, the 12 hourly updates for the Southern Hemisphere systems isn't really good enough IMO but they tend to be as accurate as anyone else I find in their forecasts. I must admit I do use JMA a bit despite the 10-min wind average, mainly because they name west pacific storms. The IMD (bless them) always underestimate windspeeds IMO. To me, Tropical Cyclone Nargis had winds far stronger than the 90kts they observed.

Haha, lol. He was taking in some dry air from the Australian mainland.

Look at this beauty. 10-min sustained winds of 115kts. Pah! 1-min sustained= 145kts, much better, lol