Thoughts on Saffir-Simpson scale...

[millibar]

...after reviewing data on Isabel and others, don't you guys and gals think it's time for the NHC to upgrade it's current intensity rating scale? Some cases in point:
1) a weak Cat 2 Isabel with a Cat 4/5 stormsurge = Cat 3/4 damage.
2) a Cat 1/TS slow-moving Allison = Cat 3+ flood damage
3) a Cat 3 (probably Cat 2 at landfall at ILM) Floyd with tons of rain = Cat 4/5 damage to a large area.
Please note: I'm not flaming the NHC; they do a most excellent job!! It's just that sometimes the intensity forecast currently in existance is way inaccurate in portraying the potential total damage any given storm may inflict on an area...

Just my thoughts, any comments???

Regards,
Millibar

PS: I'm relatively new to this board, so if this topic has already been covered, please excuse me (if this is the case, I would like to hear what the results were).

[Thunder44]

No, I don't think it needs to be upgrade or updated. I think it potrays an accurate asessment of the intensity of the tropical cylcone and how much damage it can cause under normal circumstances. However, there can be unusual circumstances that might have storm cause more or less damage than one would expect.

A slow moving weak TS or TD over land can dump alot of rainfall that can cuz a tremendous amount of flooding. A weakened hurricane making landfall can cuz a higher storm surge than expected cuz it takes more time for the seas to go down from when it was stronger. I think the best thing do for people to do is take every tropical cyclone seriously, no matter how weak it may seem.

[Dean4Storms]

No, I think the scale is fine and with any scale there is always a variable within any category. Such as previously drenched soil allowed winds of 50-60mph to topple tree's more easily.


I'm of the opinion though that along with the 5 Day forecast now issued by the NHC that an additional potential strike category should be added.


We cover 24-48 hrs. with a Hurricane Watch and under 24hrs with a Warning. Maybe we need to come out with something like a Hurricane Threat category for potential out to 48-72hrs. With the advances in technology folks were seeing the threat of Issa 3-4 days prior and many were preparing anyway so why not add a new category that would encompass a larger area of coastline and advise people in this category to check supplies, medicines and stay abreast of latest advisories. The system were using now dates back to black and white TV's I think.

[wxman57]

I agree with Thunder44. The current scale worked (works) just fine. Isabel produced wind and surge damage very much like a weak Cat 2 storm.

And you CERTAINLY didn't see a Cat 4/5 storm surge or wind damage there. From what I've seen, there was a surge of 9 ft or less. Remember that storm surge values are not valid for inlets/bays. Storm surge in a bay with onshore winds can be twice as high as at the coast. If that area had been hit from the same direction by a Cat 4/5 storm then there would be nothing left behind but sand (if that). That was nowhere near Cat 4/5 wind damage. A Cat 5 wind of 160 mph with gusts to near 190-200 mph would be about 4 times as strong as what Hatteras experienced. You just can't imagine the force of a major hurricane. But if you were on Hatteras last Thursday, you got a little hint.

As for rainfall, Allison wasn't even a TD when it produced the noctournal "core rainfall" episode in Houston 2 years ago. It was just a small remnant low. Rainfall is independent of hurricane intensity, and is not even part of the Saffir-Simpson scale.

[wxman57]

I'm of the opinion though that along with the 5 Day forecast now issued by the NHC that an additional potential strike category should be added.

We cover 24-48 hrs. with a Hurricane Watch and under 24hrs with a Warning. Maybe we need to come out with something like a Hurricane Threat category for potential out to 48-72hrs. With the advances in technology folks were seeing the threat of Issa 3-4 days prior and many were preparing anyway so why not add a new category that would encompass a larger area of coastline and advise people in this category to check supplies, medicines and stay abreast of latest advisories. The system were using now dates back to black and white TV's I think.

One problem I see in the 5-day track is that the NHC will always show the same amount of uncertainty no matter how high the confidence level in a track. Surely, there wasn't 400-500 miles of uncertainty at 120 hours once Isabel began turning NW. I have never seen such model agreement as with Isabel. Now it would be interesting if they did what we do for our customers -- narrow down the cone and put a confidenc level as a percentage inside the probability cone. With each storm, the cone would be different - sometimes wide, sometimes narrow, sometimes with two lobes indicating possible alternate tracks. Could be interesting.

[ColdFront77]

As I have been saying over the course of the last several weeks, tropical systems generally are difficult to forecast, thus having "the cone" indicating the margin of error in time makes perfect sense.

[wxman57]

As I have been saying over the course of the last several weeks, tropical systems generally are difficult to forecast, thus having "the cone" indicating the margin of error in time makes perfect sense.

Oh, I agree with the "cone of uncertainty", but I disagree that the uncertainty is the same for each storm. Just indicating the average error over the past decade or two doesn't do very much to indicate confidence levels in the current forecast track.

[ColdFront77]

As I have been saying over the course of the last several weeks, tropical systems generally are difficult to forecast, thus having "the cone" indicating the margin of error in time makes perfect sense.

Oh, I agree with the "cone of uncertainty", but I disagree that the uncertainty is the same for each storm. Just indicating the average error over the past decade or two doesn't do very much to indicate confidence levels in the current forecast track.

I wasn't saying I disagreed with you, wxman. I felt like responding and it may have come out that way. Thanks.

[millibar]

...sorry you misinterpred a portion of my post. I did NOT call Isabel a Cat 5 storm, but I strongly disagree with your assessment of the storm surge. It was definitely greater than a Cat 2 surge, even allowing for bays and inlets.The KDH area as well as the Buxton/Hatteras village areas were not inlets or bays (that obviously has changed for Hatteras village now). The simple point I was trying to make was this: people (whether rightly or wrongly) tend to make their evacuation assessment based on the stated strength of the storm by the NHC. OBX residents are not novices when it comes to 'canes, especially the natives. The hard fact is that Isabel's category status prior to landfall grossly undedestimated it's overall effects! As the coastal population continues to increase with people who have no firsthand knowledge of one of Nature's most awesome displays, I really feel it is time to "upgrade" the current categorizing of tropical systems.

Thanks for your responses, this is how one learns things. Just hoping we have a friendly exchange of ideas. If not, I apologize to the board and everyone involved. :?

With BEST regards,
Millibar

[Derek Ortt]

Those surge values are valid for south Florida only. This is the least storm surge prone area the entire US mainland (possibly entire USA as the waves are also broken up by the Bahamas, unlike Hawaii). The 18+ feet are for cat 5 hurricanes hitting s fla. The 9 to 12 feet for a 3 is for s fla. For all other areas of the coats, a 90KT hurricane is expected to cause a storm surge of about 10 feet.

Isabel was a 90KT storm at landfall, not a major hurricane (and not a weak cat 2 either as evidenced by H-wind output)