5 ms·

We're only beginning to understand the historic nature of Helene's flooding

52 points by rntn 2y ago

bloopernova 2y ago
Accumulated Cyclone Energy (ACE) https://tropical.atmos.colostate.edu/Realtime/ https://tropical.atmos.colostate.edu/Realtime/ The figure in parentheses is ACE, averaged over 30 years up to and including September 30th: 77.8 (94.1) There's more detail here, including a helpful chart: https://tropical.atmos.colostate.edu/Realtime/index.php?loc=northatlantic https://tropical.atmos.colostate.edu/Realtime/index.php?loc=... EDIT: Interesting that Beryl had more ACE than Helene. I wonder if that figure will change as the effects from Helene are investigated further?
- sudenmorsian 2y ago
  No, Helene's ACE will remain unchanged until the post-season analysis of both storms. It's a measure of the storm's duration and intensity; Helene was a rather short-lived storm with the intense period only occuring for a short time compared to Beryl which is why it has such a lower value than Beryl. https://en.wikipedia.org/wiki/Accumulated_cyclone_energy https://en.wikipedia.org/wiki/Accumulated_cyclone_energy
- dredmorbius 2y ago
  For more information there's a Wikipedia entry: <https://en.wikipedia.org/wiki/Accumulated_cyclone_energy https://en.wikipedia.org/wiki/Accumulated_cyclone_energy> I'm unfamiliar with the term, or what it means, though the concept seems interesting. What it apparently isn't, is a measure of the total available or potential storm energy within a basin, which seems to me an interesting concept. I'd presume that would mostly be dependent on sea surface temperature, and SST might well be the best measure of that which exists. If ACE is the total energy released via cyclonic storms, then the ACE:TPSE ratio might indicate future risk within a storm season for a basin. Storm incidence is predicated on other factors, so far as I understand most especially high-altitude wind shear and total humidity. High wind shear and low humidity can both depress storm formation and development, and may have been a factor in the August lull for the 2024 North Atlantic hurricane season.
danielvf 2y ago
It was a bad disaster. I was scheduled to be there, but took a look at the NOAA rainfall map the night before and canceled my trip. Calling it unthinkable is really overselling it though. Mountain towns and roads flood when it rains a lot. If you search past years google search results for Chimney Rock, it floods with 3" to 5" inches of rain. The town is just a few feet above water level - I've walked along the river.
- schiffern 2y ago
  So you're saying it's a region already especially vulnerable to flooding. How is that supposed to be better?
  - jjk166 2y ago
    They're not saying it was better, they're saying it was foreseeable.
    - schiffern 2y ago
      Doh! Thanks, that makes sense.
- giraffe_lady 2y ago
  I think they mean more literally historical, in the sense that like this is when people will remember becoming aware that inland mountain ranges are catastrophically vulnerable to hurricanes now. > Meteorologist Ben Noll said that the level of moisture transported to western North Carolina is more than 1.5 times greater than any event in the historical record for the region. This is a little more than "mountains flood when it rains" it seems.
- saltminer 2y ago
  > Mountain towns and roads flood when it rains a lot. > Chimney Rock, it floods with 3" to 5" inches of rain. This was no ordinary flood - Chimney Rock was basically wiped off the map. This isn't a "dry it out and replace the sheetrock" situation, most of the town is gone. That's not to say building several feet above a mountain river is a smart idea (or any river, for that matter), but this level of destruction hasn't been seen since the 1916 flood.
blackeyeblitzar 2y ago
What did people expect when they built in floodplains with no flood insurance? My question is why taxpayers have to keep subsidizing the cleanup and rebuilding in these areas.
- zem 2y ago
  think of it as your taxes and their taxes both paying into a national disaster insurance scheme run by the government.
  - xingped 2y ago
    I'd agree, but if it's a floodplain, I think it's fair to be annoyed when you pay taxes into this fund AND you pay into your own insurance, yet a bunch of folks choose not to buy insurance when they should and expect to get paid out of this fund instead. It should be a last resort, not an "I just decided not to buy my own insurance" backup plan.
    - zem 2y ago
      there is very little living space in the US that is not subject to some sort of natural disaster. where i live in california, e.g., fire insurance is getting increasingly expensive and many insurance companies are opting out of offering it altogether. what you should be annoyed about is that you have to pay for private natural disaster insurance on a per-disaster-type basis rather than the government explicitly providing a national pool by default. edit: also it's worth considering that the worse the land in terms of risk, the poorer the people who will be forced to live there because they were priced out of everything else. with climate change accelerating this will increasingly be a factor, and it is unconscionable to expect those people to bear the burden of insurance themselves. this is what a civilisation is for.
      - none4methx 2y ago
        We should also fix the part where some dunce with a letter put a town where physics (at least occasionally) put a river. What we call a civilization should have education at least equivalent to a seven year old sand castle architect. Not hubris so large we go broke attempting to occupy the waterspouts of the world just because there’s pipe and cable there.
aaron695 2y ago
[dead]
deleted 2y ago
[deleted]
boesboes 2y ago
Either i am having the biggest case of deja vu ever, or this post has time travelled. I am certain i read this exact post and comments 2 or 3 days ago.
- deleted 2y ago
  [deleted]
- eat_veggies 2y ago
  when a post enters the second chance pool, the timestamps of the post and comments get rewritten. if you hover over a timestamp you can see its original value.
jmward01 2y ago
I was supposed to be there Monday. I am flying out Friday instead. My family, obviously, doesn't have power and water yet. The best estimates they have are a month for water and power may come back in the next few days. I26 north I40 west are impassible and may be that way for months. Friends businesses are gone. It is a mess. I plan on doing the only thing that non-emergency people should do in things like this: drive my family out of there as soon as I arrive. Fewer people = fewer problems. As to what got us here? Bad things happen to well prepared places (Japan in 2011?) but having lived in truly well prepared places, I gotta argue that US infrastructure and planning isn't great compared to a lot of other countries (definitely better than some though). Infrastructure always pays for itself in the long term but we have so much short term, selfish, anti-science thinking that it is scary.
- falcolas 2y ago
  > I26 north I40 west are impassible and may be that way for months. The latest I've heard is they're expected to be fixed by Sept 2025. So just shy of a year.
TYPE_FASTER 2y ago
We had flooding in Vermont on the same day in July as last summer’s flooding. In a different deluge, one town had 8” of rain in six hours. It would appear this is the new normal. Towns will have to be redesigned (some were built around rivers for power and transportation a long time ago).
OutOfHere 2y ago
Insurance companies are undoubtedly moving out from servicing the areas. Voters continue to vote as if carbon dioxide and methane are not greenhouses gases that they emit. Such across-the-board denial of reality can have only one consequence: elimination.
- GenerWork 2y ago
  Insurance companies probably won't be hit as hard as people think they will be. How many people in that area had flood insurance? Very few Americans have flood insurance, and they're generally concentrated in areas where there's storm surge, i.e. the coasts.
  - falcolas 2y ago
    Unfortunately, a number of flooded properties were located outside the FEMA designated flood zones - even the 100 year+ zones. And they were located higher than the flood lines by something around 10-12 feet (in Ashville, NC). I really hope a lot of changes are made coming out of this disaster.
    - GenerWork 2y ago
      FEMA will definitely redraw some flood zones after this.
tzs 2y ago
If you want to get a feel for what some of the rain people are talking about is like, see if you can find a model of rainfall intensity for your area. A good place to look is on the websites of your state government departments that have to deal with drainage and runoff. For example here in Washington that would be the Department of Transportation. They need to be estimate how often a given area will get X inches of rain over Y minutes for a range of X and Y in order to figure out things like how big a culvert they need to put under a road. That information is in chapter 2 of their hydraulics manual which the public can download [1]. When someone mentions some ungodly amount of rain in a flood area, such as the 8" in 6 hours mentioned in another comment, you can take that rate (1.33"/hr) and then see how often you expect to see that rate where you are and for how long. Doing that for my location, I expect to see 1.33"/hr every 2 years--but only for 8.5 minutes at a time. Every 5 years I can expect to see it for nearly 14 minutes. 18 minutes every 10 years. 25 minutes every 25 years. 32 minutes every 50 years. 38 minutes every 100 years. Basically, then, if I think back over the last couple of years or so and remember the worst 8 minutes of rain I had, and then imagine it going on for 6 hours instead of just being an 8 minute pulse I'll have some idea of how much freaking rain that was. Alternatively, I can see that I expect an interval of 6 hours with 0.19" of rain every 2 years, 0.24" every 5 years, 0.28" every 10 years, 0.33" every 25 years, 0.37" every 50 years, and 0.40" every 100 years. So people who got 8" in 6 hours got 20 times as much rain as people where I live expect to see in 6 hours if they live here their entire life. I'm curious what rates they get in those storms over shorter periods, such as 5 minutes. My tipping rain gauge takes about 100 ms to complete a tip, and it tips every 0.11", so if there was a spurt with intensity above 396"/hr it would not be able to keep up. Can those storms hit that over short intervals? [1] https://wsdot.wa.gov/engineering-standards/all-manuals-and-standards/manuals/hydraulics-manual https://wsdot.wa.gov/engineering-standards/all-manuals-and-s...

52 points by rntn 2y ago

Accumulated Cyclone Energy (ACE) https://tropical.atmos.colostate.edu/Realtime/ https://tropical.atmos.colostate.edu/Realtime/ The figure in parentheses is ACE, averaged over 30 years up to and including September 30th: 77.8 (94.1) There's more detail here, including a helpful chart: https://tropical.atmos.colostate.edu/Realtime/index.php?loc=northatlantic https://tropical.atmos.colostate.edu/Realtime/index.php?loc=... EDIT: Interesting that Beryl had more ACE than Helene. I wonder if that figure will change as the effects from Helene are investigated further?

sudenmorsian 2y ago
No, Helene's ACE will remain unchanged until the post-season analysis of both storms. It's a measure of the storm's duration and intensity; Helene was a rather short-lived storm with the intense period only occuring for a short time compared to Beryl which is why it has such a lower value than Beryl. https://en.wikipedia.org/wiki/Accumulated_cyclone_energy https://en.wikipedia.org/wiki/Accumulated_cyclone_energy
dredmorbius 2y ago
For more information there's a Wikipedia entry: <https://en.wikipedia.org/wiki/Accumulated_cyclone_energy https://en.wikipedia.org/wiki/Accumulated_cyclone_energy> I'm unfamiliar with the term, or what it means, though the concept seems interesting. What it apparently isn't, is a measure of the total available or potential storm energy within a basin, which seems to me an interesting concept. I'd presume that would mostly be dependent on sea surface temperature, and SST might well be the best measure of that which exists. If ACE is the total energy released via cyclonic storms, then the ACE:TPSE ratio might indicate future risk within a storm season for a basin. Storm incidence is predicated on other factors, so far as I understand most especially high-altitude wind shear and total humidity. High wind shear and low humidity can both depress storm formation and development, and may have been a factor in the August lull for the 2024 North Atlantic hurricane season.

danielvf 2y ago

It was a bad disaster. I was scheduled to be there, but took a look at the NOAA rainfall map the night before and canceled my trip. Calling it unthinkable is really overselling it though. Mountain towns and roads flood when it rains a lot. If you search past years google search results for Chimney Rock, it floods with 3" to 5" inches of rain. The town is just a few feet above water level - I've walked along the river.

schiffern 2y ago
So you're saying it's a region already especially vulnerable to flooding. How is that supposed to be better?
- jjk166 2y ago
  They're not saying it was better, they're saying it was foreseeable.
  - schiffern 2y ago
    Doh! Thanks, that makes sense.
giraffe_lady 2y ago
I think they mean more literally historical, in the sense that like this is when people will remember becoming aware that inland mountain ranges are catastrophically vulnerable to hurricanes now. > Meteorologist Ben Noll said that the level of moisture transported to western North Carolina is more than 1.5 times greater than any event in the historical record for the region. This is a little more than "mountains flood when it rains" it seems.
saltminer 2y ago
> Mountain towns and roads flood when it rains a lot. > Chimney Rock, it floods with 3" to 5" inches of rain. This was no ordinary flood - Chimney Rock was basically wiped off the map. This isn't a "dry it out and replace the sheetrock" situation, most of the town is gone. That's not to say building several feet above a mountain river is a smart idea (or any river, for that matter), but this level of destruction hasn't been seen since the 1916 flood.

blackeyeblitzar 2y ago

What did people expect when they built in floodplains with no flood insurance? My question is why taxpayers have to keep subsidizing the cleanup and rebuilding in these areas.

zem 2y ago
think of it as your taxes and their taxes both paying into a national disaster insurance scheme run by the government.
- xingped 2y ago
  I'd agree, but if it's a floodplain, I think it's fair to be annoyed when you pay taxes into this fund AND you pay into your own insurance, yet a bunch of folks choose not to buy insurance when they should and expect to get paid out of this fund instead. It should be a last resort, not an "I just decided not to buy my own insurance" backup plan.
  - zem 2y ago
    there is very little living space in the US that is not subject to some sort of natural disaster. where i live in california, e.g., fire insurance is getting increasingly expensive and many insurance companies are opting out of offering it altogether. what you should be annoyed about is that you have to pay for private natural disaster insurance on a per-disaster-type basis rather than the government explicitly providing a national pool by default. edit: also it's worth considering that the worse the land in terms of risk, the poorer the people who will be forced to live there because they were priced out of everything else. with climate change accelerating this will increasingly be a factor, and it is unconscionable to expect those people to bear the burden of insurance themselves. this is what a civilisation is for.
    - none4methx 2y ago
      We should also fix the part where some dunce with a letter put a town where physics (at least occasionally) put a river. What we call a civilization should have education at least equivalent to a seven year old sand castle architect. Not hubris so large we go broke attempting to occupy the waterspouts of the world just because there’s pipe and cable there.

aaron695 2y ago

[dead]

deleted 2y ago

[deleted]

boesboes 2y ago

Either i am having the biggest case of deja vu ever, or this post has time travelled. I am certain i read this exact post and comments 2 or 3 days ago.

deleted 2y ago
[deleted]
eat_veggies 2y ago
when a post enters the second chance pool, the timestamps of the post and comments get rewritten. if you hover over a timestamp you can see its original value.

jmward01 2y ago

I was supposed to be there Monday. I am flying out Friday instead. My family, obviously, doesn't have power and water yet. The best estimates they have are a month for water and power may come back in the next few days. I26 north I40 west are impassible and may be that way for months. Friends businesses are gone. It is a mess. I plan on doing the only thing that non-emergency people should do in things like this: drive my family out of there as soon as I arrive. Fewer people = fewer problems. As to what got us here? Bad things happen to well prepared places (Japan in 2011?) but having lived in truly well prepared places, I gotta argue that US infrastructure and planning isn't great compared to a lot of other countries (definitely better than some though). Infrastructure always pays for itself in the long term but we have so much short term, selfish, anti-science thinking that it is scary.

falcolas 2y ago
> I26 north I40 west are impassible and may be that way for months. The latest I've heard is they're expected to be fixed by Sept 2025. So just shy of a year.

TYPE_FASTER 2y ago

We had flooding in Vermont on the same day in July as last summer’s flooding. In a different deluge, one town had 8” of rain in six hours. It would appear this is the new normal. Towns will have to be redesigned (some were built around rivers for power and transportation a long time ago).

OutOfHere 2y ago

Insurance companies are undoubtedly moving out from servicing the areas. Voters continue to vote as if carbon dioxide and methane are not greenhouses gases that they emit. Such across-the-board denial of reality can have only one consequence: elimination.

GenerWork 2y ago
Insurance companies probably won't be hit as hard as people think they will be. How many people in that area had flood insurance? Very few Americans have flood insurance, and they're generally concentrated in areas where there's storm surge, i.e. the coasts.
- falcolas 2y ago
  Unfortunately, a number of flooded properties were located outside the FEMA designated flood zones - even the 100 year+ zones. And they were located higher than the flood lines by something around 10-12 feet (in Ashville, NC). I really hope a lot of changes are made coming out of this disaster.
  - GenerWork 2y ago
    FEMA will definitely redraw some flood zones after this.

tzs 2y ago

If you want to get a feel for what some of the rain people are talking about is like, see if you can find a model of rainfall intensity for your area. A good place to look is on the websites of your state government departments that have to deal with drainage and runoff. For example here in Washington that would be the Department of Transportation. They need to be estimate how often a given area will get X inches of rain over Y minutes for a range of X and Y in order to figure out things like how big a culvert they need to put under a road. That information is in chapter 2 of their hydraulics manual which the public can download [1]. When someone mentions some ungodly amount of rain in a flood area, such as the 8" in 6 hours mentioned in another comment, you can take that rate (1.33"/hr) and then see how often you expect to see that rate where you are and for how long. Doing that for my location, I expect to see 1.33"/hr every 2 years--but only for 8.5 minutes at a time. Every 5 years I can expect to see it for nearly 14 minutes. 18 minutes every 10 years. 25 minutes every 25 years. 32 minutes every 50 years. 38 minutes every 100 years. Basically, then, if I think back over the last couple of years or so and remember the worst 8 minutes of rain I had, and then imagine it going on for 6 hours instead of just being an 8 minute pulse I'll have some idea of how much freaking rain that was. Alternatively, I can see that I expect an interval of 6 hours with 0.19" of rain every 2 years, 0.24" every 5 years, 0.28" every 10 years, 0.33" every 25 years, 0.37" every 50 years, and 0.40" every 100 years. So people who got 8" in 6 hours got 20 times as much rain as people where I live expect to see in 6 hours if they live here their entire life. I'm curious what rates they get in those storms over shorter periods, such as 5 minutes. My tipping rain gauge takes about 100 ms to complete a tip, and it tips every 0.11", so if there was a spurt with intensity above 396"/hr it would not be able to keep up. Can those storms hit that over short intervals? [1] https://wsdot.wa.gov/engineering-standards/all-manuals-and-standards/manuals/hydraulics-manual https://wsdot.wa.gov/engineering-standards/all-manuals-and-s...