by Bob Henson, NCAR News with contributions from Dr. Ryan Maue
Every so often, a quiet corner of research suddenly grabs the spotlight. Such was the case this week when a Category 1 Atlantic hurricane morphed into Superstorm Sandy (note- it wasn’t a hurricane when it made landfall, it was an extratropical cyclone – Anthony), wreaking tens of billions of dollars in damage and taking scores of lives in the eastern United States.
Sandy’s destiny as a hybrid storm was flagged to the public several days before landfall, when the irresistible name “Frankenstorm”—coined by a NOAA meteorologist—went viral. (Of course, in the original Mary Shelley novel, it was the scientist rather than the monster who was dubbed Frankenstein, as Bay Area meteorologist Jan Null pointed out to me.)
While there have been hybrid storms before, Superstorm Sandy was a creation distinct in meteorological annals, as it pulled together a variety of familiar ingredients in a unique way. Sandy could be the storm that launches a thousand dissertations—or at least a few—and some of its noteworthy aspects have implications for hurricane warning in general. Warning: there’s a bit of unavoidable weather geekery in the material below, although I’ll try to keep it as accessible as possible.
When a hurricane shapeshifts
Extratropical transition is the formal name for what happened in the 12 to 24 hours before Sandy crashed ashore near Atlantic City on Monday evening, 29 October. “Extratropical” means “outside the tropics,” so technically speaking, it would apply to any cyclone (low-pressure center) that’s located in the midlatitudes or polar regions. But there’s a more basic distinction used by meteorologists: whether a low is warm-core or cold-core.
A hallmark of tropical cyclones (known as hurricanes, typhoons, or cyclones in various parts of the world) is that their circulations revolve around a core of warm air. Hurricanes draw energy from oceanic heat and moisture, and they thrive when the surrounding air is uniformly warm and humid and upper-level winds steering the storm are relatively weak. In contrast, an extratropical low is typically positioned at or near the intersection of a cold front and warm front. Such a low is helped rather than hindered by temperature and moisture contrasts and the accompanying strong winds of the polar jet stream.
A much-studied storm
One of the strongest extratropical lows in Atlantic history occurred in January 1989 during the ERICA field project. It was one of the most intense wintertime storms ever observed in that region: air pressure at the surface dipped as low as 928 millibars (27.40 inches of mercury), comparable to the pressure in a Category 3 or 4 hurricane.
The graphic above shows winds at the 850 hPa level, about a mile above the sea surface, with a warm seclusion visible as an eye-like feature on the west side of the storm. (Click on image for an enlarged version, including wind speed legend.)
The YouTube visualization linked below illustrates the evolution of this cyclone.
(Image above courtesy Ryan Maue, WeatherBell; visualization below by Mel Shapiro and Alan Norton, NCAR, and Ryan Maue.)
Here are three of the routes that warm- and cold-core systems can take as they evolve:
- It’s not unusual at all for a tropical cyclone to shift from warm-core to cold-core. In an average year, one or more hurricanes will evolve into extratropical storms in a fairly straightforward manner as they move into the North Atlantic. As colder, drier air intrudes into the warm core, the storm typically loses symmetry and begins tilting toward the coldest upper-level air.
- It’s also possible for an extratropical cyclone to develop what’s known as a warm seclusion. In this case, a pocket of warm, moist air is drawn into the cold-core circulation, then pinched off through a complicated set of dynamics involving air pulled down from the stratosphere. This is dubbed the Shapiro-Keyser process, after veteran researchers Mel Shapiro (now at NCAR) and Daniel Keyser (University of Albany, State University of New York). Some of the Atlantic’s most intense storms of any type have emerged from warm seclusions (see animation above). These are most common in winter over the far North Atlantic, but rarely do they move onto the mid-Atlantic coast, especially in mid-autumn.
- Once in a while, an extratropical cyclone will get a boost of energy by absorbing the remnants of a hurricane. Well east of New England, the iconic “perfect storm” of October 1991 was fueled by heat and moisture from the late Hurricane Grace. While it never moved ashore, this great storm still pushed destructive surf into much of the U.S. East Coast.
And then there’s Sandy . . .
Meteorologists are still parsing the maps, but it appears that Sandy may have incorporated elements from all three of the above processes. While Sandy was still a hurricane, the storm’s outer edges began to reveal some aspects of an extratropical cyclone, with an enormous zone of strong surface wind and “a great chimney of upper-level outflow,” as Shapiro puts it (see satellite image.) The storm’s warm core briefly intensified about a day before landfall (see diagram).
Then, a few hours before landfall, Sandy began a sharp curve toward the west, moving toward the heart of the approaching midlatitude trough of low pressure. In Shapiro’s view, this marked an apparent warm seclusion trying to take place on top of the storm’s fast-decaying warm core.
I asked Shapiro how often he’s seen a storm like Sandy. He replied, “Never.”
The one that may come closest in Shapiro’s view is the “Long Island Express” hurricane of 1938, which killed hundreds of New Englanders as it slammed ashore virtually without warning. “There was a dramatic upper trough coming in from Canada, just like there was with Sandy,” says Shapiro. The 1938 storm raced northwards at speeds of close to 70 mph, making it the fastest-moving hurricane on record, and hooked northwest after landfall. While not as much of a speed demon, Sandy did accelerate to a forward motion of nearly 30 mph as it curved west and approached New Jersey. Upper-air observations from the 1930s are sparse, however, so it might not be possible to pin down the commonalities between the two events.
Two storms in one?
Chris Davis, head of NCAR’s Advanced Study Program, has carried out extensive research on how warm- and cold-core processes interrelate. Like Shapiro, Davis finds Sandy an intriguing case. “It seems to have had a remnant inner core that was somewhat tropical, embedded in a much larger nontropical structure,” says Davis. He notes other cases where a remnant warm core can persist well into a storm’s extratropical life. “You end up with two definable structures at once,” he says. “There was a point where you had a huge arc of cloud over land, but you also had a complete eyewall surrounding the inner core.”
Sandy’s vast wind field provides more evidence for the warm-within-cold theory. Along with a small central core of winds near hurricane force, focused on Sandy’s south side, there was a second maximum of high wind well to the north. It pounded portions of New England with wind gusts as high as 86 mph in Rhode Island. This outer wind band later moved into Long Island and New York City.
This dual wind structure isn’t a common occurrence with hurricanes. Fortunately, computer models predicted the unusual outer band of high wind more than a day ahead of time. And upper-air observations caught its development several thousand feet above ground a few hours before the winds mixed down to the surface. As a result, the National Weather Service provided a specific “nowcast,” putting people in the New York area—especially those in skyscrapers—on alert that dangerous hurricane-force gusts could occur in a window of several hours on Monday evening. Gusts reached 90 mph at Islip, in central Long Island, and 79 mph at John F. Kennedy International Airport, in Brooklyn.
There’s still much to digest about the physics of this remarkable weather event, not to mention the host of societal issues it’s raised. What’s heartening to researchers is that computer models, by and large, predicted many of Sandy’s most unusual features days ahead of time. That gave forecasters confidence in predicting unprecedented impacts to the most densely populated part of the nation, regardless of whether Sandy was dubbed a hurricane, an extratropical storm, a hybrid, or—in the label that now seems to be winning out—a “superstorm.”
Sandy’s circuitous life: This “phase diagram” from Robert Hart (Florida State University) shows how the storm’s characteristics changed from point A (0000 UTC on October 22, when Sandy was forming in the Caribbean Sea) to point C (1200 UTC on October 31, when Sandy’s remnant low had moved near Lake Erie). Dots are indicated every six hours; warmer colors denote lower pressure and thus a stronger system. Beginning at point A with the structure of a typical hurricane (symmetric warm-core), Sandy became asymmetric as it grew in size. The storm quickly became an asymmetric cold-core low near landfall and a symmetric cold-core low as it decayed. The kink in the curve at upper right corresponds to the strengthening of Sandy’s inner core about a day before landfall. Click on image to see the full diagram. The phase diagrams are explained in a 2003 article in Monthly Weather Review. Find more background and other phase diagram examples here. (Image courtesy Robert Hart, FSU.)
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eyesonu
There is another string in WUWT on that topic which has some very good discussions about the question you raise.
D B
To repeat: I will not engage with you in discussion again until you have withdrawn your vicious and baseless personal attacks.
Howskepticalment says:
November 3, 2012 at 6:37 pm
philincalifornia
Just as the phrase “think of the children” already has, the word “unprecedented” is rapidly approaching joke status.
In relation to the term ‘unprecendented’, it is not all that funny that people prefer sarcasm, logical fallacies, personal abuse and sophistry to rational discussion.
+++++++++++
You’re right, it’s not funny at all. People are dying because of idiots like you.
Show some evidence
……
tick tock
philincalifornia says to howskepticalment:
“People are dying because of idiots like you.”
Be careful, Phil. Even though you’re right, Mr S can’t take criticism like that. He’s new here, so he doesn’t understand that I and others have been called a lot worse things by alarmist commenters. But then I’m not a thin-skinned crybaby, and I don’t let things like that give me an excuse to dodge answering.
Finally, Mr S seems afraid to make his own arguments, instead always referring to the author — who we can’t seem to question. If S made his own case instead of handing the ball off, I would have some respect for him. But then he would have to defend his position with logic, and answer questions. If he did that, pretty soon he would be tied up like a pretzel.
philincalifornia
First you say it is a ‘joke’ then you say it is ‘not funny’. That is inconsistent. The use of personal abuse by way of name calling further undermines your claim to any credibility.
You ask for evidence. If you read Henson’s post at the start of the string you will see evidence that demonstrates that Hurricane Sandy is unprecedented.
I can understand why some people might want to deny that this term is appropriate. But, if they do want to deny it, they will have to demolish in detail the evidence and the arguments put forward by Henson in the post above.
No poster on this string has bothered to even try.
B.S. NCAR has been filled with psychotic bull ever since Trenberth (Trenberth-Mann) arrived!
The extinction of the Cyclops Trenberth-Mann is coming soon! Good for us all that we survived and Trenberth-Mann will lie in a bloody pile of goo and puss at the bottom of a 6-foot deep hole.
XD
You’re on the wrong site dude.
Apparently someone had a tachyon radar in operation; the caption of the image near the “Two Storms in One?” heading refers to Monday 29 November. However, 29 November will be a Thursday.
?? 😉 ??
Hopefully Bronco Bamma will be re-elected. He can order a congressional committee to regulate storms. Unprecedented storms which do not conform to government structural standards will be banned by statute. He can appoint an Examiner of Storms to make sure it never happens again. That will make this senseless argument unnecessary.
/sarc?
p
[You’re on the wrong site dude
Why, because Hurricane Sandy is unprecedented, within the limits of our knowledge, and you don’t like the fact?
I trust that you are not trying to censor me or that your are saying that there is something wrong about the site?
Not one of my posts has failed moderation. I abide by the rules of the site. i do not post personal abuse. At times I have had to change my views on this site because of explanations that people have made. It is an interesting site in the sense that I have yet to see anyone acknowledging that they have changed their minds about anything to do with AGW. Does everyone here know it all already?
Nevertheless, at times I may have got it right because some posters resort to personal abuse and ever more extreme logical fallacies rather than discussing the issues rationally.
BTW, it is clear to me that no-one in this string has laid a glove on Henson’s post.
Howskepticalment…
…does not even understand that his ridiculous parroting of “unprecedented” is anti-science, because the Null Hypothesis has never been falsified. I doubt that H even understands the concept of the Null Hypothesis. He is clearly an alarmist tool who misuses words, and he still runs from trying to argue his case, instead constantly passing the ball to the absent Henson.
Note to Howskepticalment: There is no empirical evidence supporting AGW. None. If you disagree, I challenge you to post your testable, falsifiable evidence right here. Otherwise, you are nothing but an alarmist chump, posting debunked talking points. You have not a clue about anything ‘unprecedented’.
Run along now back to your alarmist echo chamber blogs, where they gobble up your spoon-fed propaganda nonsense. You need some new talking points, because you have posted nothing here that amounts to any testable scientific evidence. Instead, you only emit your easily debunked propaganda, misusing words as your lame argument. This is the internet’s “Best Science” site, and your pathetic nonsense has been deconstructed by everyone else. Troll away with your fake ‘unprecedented’ if you must, but the rest of us know what you’re doing. And it is not science.
Sandy is not unprecidented for being a hurricane evolving into a very
damaging extratropical cyclone.
I would like to mention Hurricane Hazel of October 1954, which landfell
near Myrtle Beach, SC as a Cat-4 hurricane.
Hazel was next getting caught-up with a frontal boundary, in an area that
is infamous for spawning Nor’Easters. Hazel transitioned to an extratropical
cyclone inland, no later than crossing the NC-VA border. And Hazel did so
with Cat-2-qualifying winds in Virginia.
And next, Hazel moved very fast, with convection assisted by tropical heat
and moisture assisting connectivity to the polar front jet stream. Hazel
achieved hurricane-qualifying winds in Philadelphia, probably from the south
or southeast.
What next – Hazel was 1954’s Frankenstorm – delivering hurricane-
qualifying winds in Toronto (especially its East York and Scarboro sections)
and 70 miles north of Toronto, as well as heavy rain causing still-standing
record flooding of the Humber River.
Both Toronto and Philadelphia have yet to be hit by hurricane-qualifying
winds by any means after October 1954.
Thank You! This wa a good primer on the basics of hurricane/cyclone fueling!
MtK
Howskepticalment says:
November 3, 2012 at 9:09 pm
In a stochastic/chaotic system, many seemingly unusual (from a human time scale perspective) weather phenomena may seem ‘unprecedented’, given the +billion year history of our planets weather and climate changes.
We have a very limited understanding of it all, supported at best by +100 years of marginally acceptable empirical data. What part of this do you object to?
MtK
The NY power grid was not upgraded partially because they have been spending all their money trying to meet the 29% renewable energy standards there. Imagine that NY city can not help themselves because of unions and green mandates. Oh – and we won’t learn from the left media that unions turned trucks around back to Alabama who were going to help get transmission lines back up in running – because they were not union. Sorry about the political attacks here, but thought it was close to the topic of this catastrophe caused by the liberals.
.
Sandy is “highly unique” … it may even be “unprecedented” once it has been studied. It is fair to say it is “close to unprecedented.” There have at best only been one or two storms in the region that were close to the characteristics of Sandy.
That said I think its silly to argue semantics over words like unprecedented. It is one thing when the word is purposely tortured and twisted, when the evidence doesn’t come close to meeting that standard. It’s another altogether here w/Sandy where were if wrong, unprecedented isn’t wrong by much.
I think there are many more interesting and important things to argue about regarding Sandy, than use of a term, that if inaccurate is barely so.
I think this post is excellent – and intriguing as to the dynamics of this storm. I still believe there was sufficient data to have called it a CAT 1 Hurricane at landfall.
Even if it had reached that level, or higher (the pressures are indicative of up to a CAT 3 as some have said) however, the NWS apparently would still not have called it a hurricane.
That is troubling – for a number of reasons.
I believe – and NWS has acknowledged – the confusion this automatic dropping of the term hurricane apparently regardless of strength, when it progressed to a certain point.
There is legitimate and serious concern that people may well have thought they could ride out the storm because it was no longer called a hurricane – thinking that “dropping” the “hurricane” status in favor of “extra-tropical low” – even though winds were gusting well into the 70-90mph range in wide areas – was the same as “downgrading” the storms strength – which the renaming did not necessary mean.
This is a serious issue – it could have adversely affected a myriad of issues and decisions. Some people will always be stupid and try to ride out the storm. Others though may have become complacent or had a false sense of security with what they thought was a downgrading of danger. Some lives may have been saved with the perceived “downgrade” of the storms severity and danger.
Additionally disaster planning could easily been affected. Many on the recovery side are laypeople when it comes to weather science. FRom FEMA failing to even put out bottled water bids until Friday!! – and now having none until Mon at earliest, to Con Ed’s recovery planning and a myriad of other similar instances – all might have acted differently had there not been a possible false sense of security from the “downgrade” to extra-tropical storm status, despite still packing hurricane force winds.
Also – by NOT being called a hurricane at landfall Gov. Cuomo – despite the massive destruction, and against a good body of evidence that hurricane force sustained and wind gusts did exist at and after landfall – has used this as excuse to tell everyone they don’t have to pay their hurricane deductibles – 1% to 5% of insured amounts.
This is plain out stupid and ignorant. Setting aside he doesn’t likely have the right – if he prevails it will provide a minor short term benefit to those in this event – and a great political “soundbite” for the election, but both the current people who might benefit and everyone else across the country with similar policies will pay a much higher premiums in the future because of the risk a silly Governor or other public official can render their policy terms meaningless.
The use of the term “extra-tropical low” in place of “hurricane” regardless of the strength and structure of the storm, clearly has serious implications – some financial and some life threatening. It IS something that needs to be addressed it would seem asap.
Clearly “one size fits all” for rating the disaster potential – death, injury and loss of property likelihood – no longer works. What would be a strong breeze for Florida, with generally lower density, and being more knowledgeable and prepared, has been shown to have massive disaster effect in NY/NJ and the region.
.
I agree it’s misleading to use wind-speed measures as though they were a proxy for threat-to-the-public, which results in the public being complacent about “mere” Tropical Storms. But that’s not a justification for “boosting” or hyping speeds to motivate preparedness (this will amount to crying wolf, which will fuel cynicism the next time around, as happened in the aftermath of Irene in NYC) or an indictment of “one size fits all” for rating disaster potential. What’s needed is a more sophisticated one size fits all measure–and/or the separation of threat measures into different tracks. Here’s what I wrote after Irene:
—————-
I don’t think we critics of the NHC are implicitly calling for less “alarm” on the part of the public. The public could have been warned repeatedly by the media that a large tropical storm will drop lots of rain, leading to flooding, and that its winds can drop lots of trees, particularly since there’s been no similarly large windstorms for years, meaning that weak, vulnerable trees near power lines haven’t been thinned. There could be an in-depth explanation of why evacuation is a good policy, even if ones home isn’t vulnerable to flooding or tree-fall: because electricity and phone service can be lost for many days, causing a crisis situation in unreachable isolated homes if emergency service (e.g., medical, fire) is needed by them.
There is plenty of time available on the media for this sort of educational material—a fraction of the time they spent on Irene. I suggest the government prepare a half-hour educational video for TV stations–and make it available on the Internet as well. (It should contain hints that local power companies should thin trees near their power lines as routine maintenance.)
………………
I suggest that the NHC categorize storms on two scales: wind speed and damage potential. The latter would take into account factors like:
* Storm surge potential (is it approaching land rapidly? perpendicularly? at high tide?)
* Tree knock-down and electric outage potential (is the ground saturated? does the storm cover a wide area? is it moving slowly? are the trees in full leaf? have there been few recent big windstorms (to thin weak trees)? have the electric utilities been lackadaisical about trimming branches over their power lines?)
* Flood potential (is the ground saturated? does the storm cover a wide area? is it moving slowly? are the rivers high? are the dams full?)
The public should be warned primarily on the basis of the damage potential estimate, not current wind speed. It could easily be educated into taking this figure more seriously than the hurricane category. (For instance, the public already has been educated to take warnings of “black ice” seriously, even though it isn’t something that can be based on any particular number.)
I suggest that the NFC call it the Threat Index, on a scale of 1 to 5, paralleling hurricane categories. An Index like that would not contaminate the wind speed classification; such contamination will lead to cynicism and disregard of their crying-wolf in the future.
Such dual-mode measurement are already commonly used: i.e., the wind-chill factor and the discomfort index (I’m guessing about the name, but it includes both heat and humidity). The public takes these measurements seriously. A third one is needed for these cyclones.
Howskepticalment says “people prefer sarcasm, logical fallacies, personal abuse and sophistry to rational discussion.”
I asked Howskepticalment what was unprecedented about Sandy. His answer was: “Read the Henson post above and then refute Henson’s claim that Hurricane Sandy was ‘unique’, aka, unprecendented.”
How is that answer not sophistry? Howskepticalment has yet to make a single statement in support of Sandy being unprecedented other than pulling the word unique out of context and equating it with unprecedented and insisting that is the correct interpretation of the word.
Earlier Howskepticalment said “It is just as well that the author did not mention the dread phrase ‘carbon dioxide’ or the stimulus-response auto function would have gone into the usual manic overdrive.”
How is that statement not sarcasm?
The author of the post said “That gave forecasters confidence in predicting unprecedented impacts to the most densely populated part of the nation” for which he was quickly and rightfully criticized. The impacts of Sandy were forecast as “unprecedented” which ended up saving many lives.
Then Howskepticalment decided unilaterally that “It is about the physical structure and dynamics of Hurricane Sandy, which, according to the author, are unprecedented.”
He apparently believes that Sandy is “unprecedented” due to this statement by the author: “While there have been hybrid storms before, Superstorm Sandy was a creation distinct in meteorological annals, as it pulled together a variety of familiar ingredients in a unique way.”
It’s now been pointed out many times that all storms are unique and that does not make them unprecedented either in structure or effects. It’s been shown that Sandy was not unprecedented in structure or effects.
It is long past time for Howskepticalment to stop smearing this forum and its participants and give direct answers to the questions put to him.
A. Scott says “It’s another altogether here w/Sandy where were if wrong, unprecedented isn’t wrong by much.”
Unprecedented is wrong. Sandy type storms happen every season in the Atlantic (see Leslie earlier this year). Sandy surge, wind and all other effects have happened to NYC before. It is pure myopia to think that Sandy is anything more than a weather coincidence.
Regarding the discussion over warnings and effects. The NHC would have been required to drop hurricane warnings if Sandy transitioned out at sea regardless of the threat to land. Therefore they chose not to issue hurricane watches and warnings even though they should have. The solutions suggested by A. Scott (call it a hurricane) and Roger Knights (determine a threat index) are both good.
But both posters have misdiagnosed the problem, it was simple and repeated in every single NHC discussion after a certain point in time: “AS NOTED IN PREVIOUS ADVISORIES…TO AVOID A HIGHLY DISRUPTIVE CHANGE FROM TROPICAL TO NON-TROPICAL WARNINGS WHEN SANDY BECOMES POST-TROPICAL…THE WIND HAZARD NORTH OF THE TROPICAL STORM WARNING AREA WILL CONTINUE TO BE CONVEYED THROUGH HIGH WIND WATCHES AND WARNINGS ISSUED BY LOCAL NATIONAL WEATHER SERVICE OFFICES.”
The “hybridization” is why the storm moved westward. Without cold air situated just to the north (and blocking it from moving north), it would have acted like any other tropical system & continued northeast.
So the westward movement & vast elongation was caused by interaction w/cold, adjacent Canadian air.
Partly correct, a cold blocking high stopped Sandy from moving north. The reason it rapidly moved west was the Fujiwhara effect (pivoting) from the short wave diving SE into the Carolinas.
A. Scott says:
November 4, 2012 at 2:29 am
“in the region”
——————————
Please don’t give the idiot any ammunition. He will conveniently forget those three words.
Howskepticalment says:
November 3, 2012 at 9:09 pm
p
You’re on the wrong site dude
Why, because Hurricane Sandy is unprecedented, within the limits of our knowledge, and you don’t like the fact?
I trust that you are not trying to censor me or that your are saying that there is something wrong about the site?
———————-
I’m resting my case.
The word “unprecedented”, and its use by people like you is going to consign it to the joke-bin of the English language. Carry on.
….. and while we’re having this cordial discussion, let me remind you that the other joke-bin phrase “save the children” has come to be a joke because, thanks to the internet, the majority of rational folk are saving their children by avoiding idiots like you.
Oh and by the way, haven’t your troupe of clowns been taxing people for what, five or ten years to mitigate these kinds of problems?
Why aren’t you claiming this as a success story ?