ATL: HELENE - Post-Tropical - Discussion

[al78]

What else is amazing is that, from tropical cyclogenesis to loss of characteristics was barely 3 1/2 days. Yet in that time it charged up to a category 4 and did historic damage.

Because of how short-lived Helene was, it only managed to generate 7.1 ACE units according to CSU, and the season is still below the 1991-2020 average ACE to date. Yet another example of shortcomings of this metric.

(For context, Isaac already generated almost half as much ACE as Helene did.)

I wouldn't call that a shortcoming of the metric, more a misinterpretation of the significance of the metric. Total ACE =/= landfalling activity even if there is a modest correlation between the two. A comparison between 2010 and 1992 is a classic illustration that it only takes one storm to make a season devastating and it doesn't need hyper-activity overall.

The main issue with ACE even if you look at ACE over land in isolation is that it doesn't take into account the extent of TS or cat 1 winds or the rainfall. Helene is a bit like Katrina in that the size of the windfield, landfall in a region prone to surge and high translational speed bringing destructive winds hundreds of miles inland were major factor in its destructiveness.

[kevin]

With a landfall intensity of 120kt/938mb, Helene is the 10th strongest hurricane to make landfall in Florida by wind speed (behind Michael, Charley and Ian this century) and the 9th most intense Florida hurricane by central pressure (behind Michael and Irma this century).

[wxman57]

We plotted the max sustained wind and gusts for Helene and the results were similar to Idalia and Francine (and 2002's Lily, 2020's Zeta). There were no reports of sustained hurricane force wind (1 min avg) inland across Florida or Georgia. However, there were plenty of reports of 95-110 mph gusts all the way up to the SC border along its track. Inland, the experience was of a strong tropical storm with Cat 2-3 wind gusts. So, what happened?

Clearly, the plane found very strong wind aloft, and maybe there were Cat 4 winds at the surface at some point offshore. However, Lily, Zeta, Idalia, Francine and Helene encountered a SW-NE jet as they approached the coast. Initially, the jet enhanced outflow and helped each storm to strengthen offshore. What aids strengthening eventually becomes detrimental wind shear. In each of these storms, the surface wind became decoupled from the stronger wind aloft. The effect was to lower the sustained surface wind but allow those stronger winds aloft to dip down. Wind gusts were nearly twice the sustained surface wind. Double the wind, four times the wind force. It doesn't take a 1-min average 100-120 mph wind to cause damage, a 10-20 second gust will produce a similar result.

Next time, keep a close eye on the predicted wind aloft as a storm nears landfall. If it's going to be encountering a jet, particularly later in the season, watch for this effect. Early season storms usually don't have to contend with the Polar jet when making landfall. They can sometimes strengthen during and even just after landfall, which produces very strong sustained wind inland but with gusts only 15-20% above sustained wind.

[chris_fit]

We plotted the max sustained wind and gusts for Helene and the results were similar to Idalia and Francine (and 2002's Lily, 2020's Zeta). There were no reports of sustained hurricane force wind (1 min avg) inland across Florida or Georgia. However, there were plenty of reports of 95-110 mph gusts all the way up to the SC border along its track. Inland, the experience was of a strong tropical storm with Cat 2-3 wind gusts. So, what happened?

Clearly, the plane found very strong wind aloft, and maybe there were Cat 4 winds at the surface at some point offshore. However, Lily, Zeta, Idalia, Francine and Helene encountered a SW-NE jet as they approached the coast. Initially, the jet enhanced outflow and helped each storm to strengthen offshore. What aids strengthening eventually becomes detrimental wind shear. In each of these storms, the surface wind became decoupled from the stronger wind aloft. The effect was to lower the sustained surface wind but allow those stronger winds aloft to dip down. Wind gusts were nearly twice the sustained surface wind. Double the wind, four times the wind force. It doesn't take a 1-min average 100-120 mph wind to cause damage, a 10-20 second gust will produce a similar result.

Next time, keep a close eye on the predicted wind aloft as a storm nears landfall. If it's going to be encountering a jet, particularly later in the season, watch for this effect. Early season storms usually don't have to contend with the Polar jet when making landfall. They can sometimes strengthen during and even just after landfall, which produces very strong sustained wind inland but with gusts only 15-20% above sustained wind.

Thank you for sharing your knowledge. Amazing and makes total sense. We're lucky to have you here.

[FrontRunner]

Given all the discussion about track forecast errors, I did a very quick look back at some of the initial forecasts while Helene was still a PTC and weak TS, and the NHC was pretty spot on. From early on they called for Helen to approach and reach MH status during the morning/afternoon of the 26th, and that's exactly what happened. Didn't quite get the sharp peak of 115-120 kts around 27/0000Z, but I believe they were almost always in the 105-110kts range. Some other folks were initially calling for strong shear and a peak only in the 70-80 kts range, which was way off.

[Kohlecane]

We plotted the max sustained wind and gusts for Helene and the results were similar to Idalia and Francine (and 2002's Lily, 2020's Zeta). There were no reports of sustained hurricane force wind (1 min avg) inland across Florida or Georgia. However, there were plenty of reports of 95-110 mph gusts all the way up to the SC border along its track. Inland, the experience was of a strong tropical storm with Cat 2-3 wind gusts. So, what happened?

Clearly, the plane found very strong wind aloft, and maybe there were Cat 4 winds at the surface at some point offshore. However, Lily, Zeta, Idalia, Francine and Helene encountered a SW-NE jet as they approached the coast. Initially, the jet enhanced outflow and helped each storm to strengthen offshore. What aids strengthening eventually becomes detrimental wind shear. In each of these storms, the surface wind became decoupled from the stronger wind aloft. The effect was to lower the sustained surface wind but allow those stronger winds aloft to dip down. Wind gusts were nearly twice the sustained surface wind. Double the wind, four times the wind force. It doesn't take a 1-min average 100-120 mph wind to cause damage, a 10-20 second gust will produce a similar result.

Next time, keep a close eye on the predicted wind aloft as a storm nears landfall. If it's going to be encountering a jet, particularly later in the season, watch for this effect. Early season storms usually don't have to contend with the Polar jet when making landfall. They can sometimes strengthen during and even just after landfall, which produces very strong sustained wind inland but with gusts only 15-20% above sustained wind.

great read as always @wxman57

[SecondBreakfast]

Anyone with Cajun navy contacts in NC? Friend of mine is frantic to find her parents in the Sherwood Forest neighborhood of Cedar Mt, NC. Landslides were reported near their home. I knew there was a number around a few years back.

[ColdMiser123]

We plotted the max sustained wind and gusts for Helene and the results were similar to Idalia and Francine (and 2002's Lily, 2020's Zeta). There were no reports of sustained hurricane force wind (1 min avg) inland across Florida or Georgia. However, there were plenty of reports of 95-110 mph gusts all the way up to the SC border along its track. Inland, the experience was of a strong tropical storm with Cat 2-3 wind gusts. So, what happened?

Clearly, the plane found very strong wind aloft, and maybe there were Cat 4 winds at the surface at some point offshore. However, Lily, Zeta, Idalia, Francine and Helene encountered a SW-NE jet as they approached the coast. Initially, the jet enhanced outflow and helped each storm to strengthen offshore. What aids strengthening eventually becomes detrimental wind shear. In each of these storms, the surface wind became decoupled from the stronger wind aloft. The effect was to lower the sustained surface wind but allow those stronger winds aloft to dip down. Wind gusts were nearly twice the sustained surface wind. Double the wind, four times the wind force. It doesn't take a 1-min average 100-120 mph wind to cause damage, a 10-20 second gust will produce a similar result.

Next time, keep a close eye on the predicted wind aloft as a storm nears landfall. If it's going to be encountering a jet, particularly later in the season, watch for this effect. Early season storms usually don't have to contend with the Polar jet when making landfall. They can sometimes strengthen during and even just after landfall, which produces very strong sustained wind inland but with gusts only 15-20% above sustained wind.

Nice analysis - the only thing I'd add is that we lost a significant chunk of the surface station network due to the east eyewall. So often times the reason why we don't record higher wind than we do are that the winds themselves broke the instrumentation.

 https://twitter.com/SteveSeman/status/1839637361510023617

[Michele B]

I'm going to guess the final cost is going to be at least $50 billion, perhaps close to $100 billion. In WNC alone, it could surpass Florence's total from the east (about $30 billion). Both Georgia and South Carolina will likely go over $10 billion, and the west coast of Florida likely will as well.

Yes, the rebuild of the infrastructure alone is going to catastrophic. Several dams, roadways, etc. then figure buildings after that. It's unfathomable.

Outside of Asheville, my great niece had a tree fall on her townhouse. She's going to try to get to her grandmother's house (my sister) 10 mins away normally, but roads are difficult. Meanwhile, there is no way to find someone to get the tree off the roof and cover the hole. Which means, if she can't find anyone, the damage INside the house will eventually make the place permanently uninhabitable.

[Michele B]

Yeah...life on the Gulf Coast is going to be rough from now on.
My parents are planning to move out of Houston soon. They're fed up with the weather disaster or two we've had every year since 2015.
I'm going to miss having a home to go back to in Houston, but...it really feels like the weather there is just going to get worse and worse.

I’m beginning to get that same thought. I grew up in coastal Louisiana and now live in Galveston County, TX and as soon as my kids are fully grown, I’m increasingly considering moving somewhere that has seasons. I’ve lived on the Gulf Coast my entire life and I honestly never thought I’d say this, but it’s getting old.

Texas Gulf Coast my whole life. What are seasons?

We are in the midst of a big move across the country as well. Getting OUT of Florida. I've been here for over 65 years....seen a LOT of hurricanes, but in my "old age" now, I just don't see myself rebuilding each time a hurricane tears everything down.

Unfortunately, we can't make the move till December, so we've still got to "endure" whatever this season is going to bring (and hope we still have a house standing to sell when we DO go!).

[CrazyC83]

I’m beginning to get that same thought. I grew up in coastal Louisiana and now live in Galveston County, TX and as soon as my kids are fully grown, I’m increasingly considering moving somewhere that has seasons. I’ve lived on the Gulf Coast my entire life and I honestly never thought I’d say this, but it’s getting old.

Texas Gulf Coast my whole life. What are seasons?

We are in the midst of a big move across the country as well. Getting OUT of Florida. I've been here for over 65 years....seen a LOT of hurricanes, but in my "old age" now, I just don't see myself rebuilding each time a hurricane tears everything down.

Unfortunately, we can't make the move till December, so we've still got to "endure" whatever this season is going to bring (and hope we still have a house standing to sell when we DO go!).

How is it different than if a major earthquake hits, say, California - or tornadoes that devastate communities in the Plains, Midwest or South? Almost everywhere has serious risks.

[MarioProtVI]

I'm going to guess the final cost is going to be at least $50 billion, perhaps close to $100 billion. In WNC alone, it could surpass Florence's total from the east (about $30 billion). Both Georgia and South Carolina will likely go over $10 billion, and the west coast of Florida likely will as well.

Preliminary estimates are already 22-34 billion. I think at least 50+ is likely.

[ObsessedMiami]

I'm going to guess the final cost is going to be at least $50 billion, perhaps close to $100 billion. In WNC alone, it could surpass Florence's total from the east (about $30 billion). Both Georgia and South Carolina will likely go over $10 billion, and the west coast of Florida likely will as well.

Yes, the rebuild of the infrastructure alone is going to catastrophic. Several dams, roadways, etc. then figure buildings after that. It's unfathomable.

Outside of Asheville, my great niece had a tree fall on her townhouse. She's going to try to get to her grandmother's house (my sister) 10 mins away normally, but roads are difficult. Meanwhile, there is no way to find someone to get the tree off the roof and cover the hole. Which means, if she can't find anyone, the damage INside the house will eventually make the place permanently uninhabitable.

I have a friend who live south of Burnsville along Seven Mile Ridge leading to Mount Mitchell. He says every single bridge is gone , from small creek crossings to major bridges crossing the South Toe River. Those people are completely
cut off and pretty low in priority for reconstruction, I’m sure.
No power, rare cell service, no well water. It’s the 19th century again up in there. He said they got about three feet of rain in the hollers there over 48 hours

[shah83]

https://www.artemis.bm/news/hurricane-h ... corelogic/

In general, it is rare for mountain areas flooding to have very high insured losses, as those communities are usually fairly poor. 2004 didn't result in huge losses, and it seems like Irene, Hazel, Agnes are the main previous hurricane with historical property losses in the deep interior. If we have more than a couple of billion in losses in western NC, it's going to be because of Buncombe county.

[Michele B]

Texas Gulf Coast my whole life. What are seasons?

We are in the midst of a big move across the country as well. Getting OUT of Florida. I've been here for over 65 years....seen a LOT of hurricanes, but in my "old age" now, I just don't see myself rebuilding each time a hurricane tears everything down.

Unfortunately, we can't make the move till December, so we've still got to "endure" whatever this season is going to bring (and hope we still have a house standing to sell when we DO go!).

How is it different than if a major earthquake hits, say, California - or tornadoes that devastate communities in the Plains, Midwest or South? Almost everywhere has serious risks.

Not going to CA. I'd rather have the days warning of a hurricane than NO warning of an earthquake!

[Teban54]

Wikipedia currently has Helene's death toll at 58:

[shah83]

Just saw an drone video of biltmore village. Damage looks pretty total. Asheville as a whole is probably hot mess. One could compare with the TN floods that got Nashville, which was about $2 billion dollars in damage.

[NXStumpy_Robothing]

We plotted the max sustained wind and gusts for Helene and the results were similar to Idalia and Francine (and 2002's Lily, 2020's Zeta). There were no reports of sustained hurricane force wind (1 min avg) inland across Florida or Georgia. However, there were plenty of reports of 95-110 mph gusts all the way up to the SC border along its track. Inland, the experience was of a strong tropical storm with Cat 2-3 wind gusts. So, what happened?

Clearly, the plane found very strong wind aloft, and maybe there were Cat 4 winds at the surface at some point offshore. However, Lily, Zeta, Idalia, Francine and Helene encountered a SW-NE jet as they approached the coast. Initially, the jet enhanced outflow and helped each storm to strengthen offshore. What aids strengthening eventually becomes detrimental wind shear. In each of these storms, the surface wind became decoupled from the stronger wind aloft. The effect was to lower the sustained surface wind but allow those stronger winds aloft to dip down. Wind gusts were nearly twice the sustained surface wind. Double the wind, four times the wind force. It doesn't take a 1-min average 100-120 mph wind to cause damage, a 10-20 second gust will produce a similar result.

Next time, keep a close eye on the predicted wind aloft as a storm nears landfall. If it's going to be encountering a jet, particularly later in the season, watch for this effect. Early season storms usually don't have to contend with the Polar jet when making landfall. They can sometimes strengthen during and even just after landfall, which produces very strong sustained wind inland but with gusts only 15-20% above sustained wind.

Good points about the jet leading to a higher-than-normal gust factor for storms undergoing trough interaction. However, the bolded section is incorrect, as Valdosta Regional Airport recorded a 102 mph sustained wind and a 133 mph gust (before it then failed). This also doesn't account for the sheer devastation in places like Keaton Beach, for example, where the tree and structural damage is pretty consistent with Category 4 landfalls of years past.

There was also dropsonde, radar velocity, and TDR data all indicating that 120-125kt was the appropriate intensity at landfall anyway.

[Ubuntwo]

We plotted the max sustained wind and gusts for Helene and the results were similar to Idalia and Francine (and 2002's Lily, 2020's Zeta). There were no reports of sustained hurricane force wind (1 min avg) inland across Florida or Georgia. However, there were plenty of reports of 95-110 mph gusts all the way up to the SC border along its track. Inland, the experience was of a strong tropical storm with Cat 2-3 wind gusts. So, what happened?

Clearly, the plane found very strong wind aloft, and maybe there were Cat 4 winds at the surface at some point offshore. However, Lily, Zeta, Idalia, Francine and Helene encountered a SW-NE jet as they approached the coast. Initially, the jet enhanced outflow and helped each storm to strengthen offshore. What aids strengthening eventually becomes detrimental wind shear. In each of these storms, the surface wind became decoupled from the stronger wind aloft. The effect was to lower the sustained surface wind but allow those stronger winds aloft to dip down. Wind gusts were nearly twice the sustained surface wind. Double the wind, four times the wind force. It doesn't take a 1-min average 100-120 mph wind to cause damage, a 10-20 second gust will produce a similar result.

Next time, keep a close eye on the predicted wind aloft as a storm nears landfall. If it's going to be encountering a jet, particularly later in the season, watch for this effect. Early season storms usually don't have to contend with the Polar jet when making landfall. They can sometimes strengthen during and even just after landfall, which produces very strong sustained wind inland but with gusts only 15-20% above sustained wind.

Good points about the jet leading to a higher-than-normal gust factor for storms undergoing trough interaction. However, the bolded section is incorrect, as Valdosta Regional Airport recorded a 102 mph sustained wind and a 133 mph gust (before it then failed). This also doesn't account for the sheer devastation in places like Keaton Beach, for example, where the tree and structural damage is pretty consistent with Category 4 landfalls of years past.

There was also dropsonde, radar velocity, and TDR data all indicating that 120-125kt was the appropriate intensity at landfall anyway.

Great points from both here. I agree that cat 4 winds did not extend beyond the coast (Keaton Beach area), but those winds were present no less.
 https://x.com/MichaelRLowry/status/1839513795661574492




A ten-second wind, yes, but 137kt essentially at surface and the large area of 125-130kt+ winds would suggest 1 minute sustained winds of at least 120kt. Dropsonde data also suggest mixing was far better than for Francine/Idalia and many other baroclinically influenced storms at landfall - even if these sustained winds did not translate inland. It was highly east weighted and it looks like almost no stations survived the east eyewall before it crossed over into Georgia.

[syfr]

https://www.artemis.bm/news/hurricane-helene-insured-wind-surge-property-loss-florida-georgia-3bn-5bn-corelogic/

In general, it is rare for mountain areas flooding to have very high insured losses, as those communities are usually fairly poor. 2004 didn't result in huge losses, and it seems like Irene, Hazel, Agnes are the main previous hurricane with historical property losses in the deep interior. If we have more than a couple of billion in losses in western NC, it's going to be because of Buncombe county.

Unlike other storms , the devastation of the infrastructure alone in WNC will top that. Miles of roads dozens and dozens of bridges, power transmission, utilities all have widespread destruction. Having spent the better part of a year shopping real estate from Boone to Brevard, I know that residential property is expensive and in short supply and there's a huge amount of it completely wrecked.

The very worst part is that there are untold people in AirBNB's, personal residences and small towns that are completely cut off from civilization with no power, water, food or transportation.