Guest Post by Willis Eschenbach
When is a hurricane not a hurricane? Well, when it doesn’t blow 64 knots (33 m/sec, 74 mph), because then it’s only a tropical storm. Inspired by a post over at the Cliff Mass Weather Blog, I’ve been trying to find a single report of sustained hurricane force winds anywhere along Irene’s path at or near landfall … no joy. I knew exaggeration was the order of the day for some folks in the climate debate, but I hadn’t realized that the illness had infected the Weather Service itself.
Figure 1. The path of Tropical Storm Irene over the mainland of the US. Symbols with a yellow center to the black storm symbol indicate a (claimed) hurricane. SOURCE ibiseye
We were fortunate in that we have very good records of the wind speed when Irene made landfall. It went almost directly over the wind recording station at Cape Lookout, at the bottom of Figure 2.
Figure 2. A closeup of Irene’s landfall. There are four wind recording stations in the area, at Beaufort (below the “70” marker at lower left), at Cape Lookout (bottom left) and at Cape Hatteras (upper right). The Onslow Buoy is located offshore, southwest of Cape Lookout.
The wind record at Cape Lookout is quite interesting, as the eye of the hurricane passed right over the anemometer there. Figure 3 shows the wind dropping as the eye went over, coincident with the deep plunge of the barometric pressure to 950 hPa.
Figure 3. TS Irene wind (light blue) and barometric pressure (violet) at Cape Lookout before, during, and after landfall. Green line at the top shows the minimum wind speed for a storm to be classified as a hurricane (64 knots).
Figure 3 shows the classic pattern of a hurricane passing directly overhead. The “eye” of the hurricane has almost no wind, and is at the center of the low pressure area. You can also see the “calm before the storm. But what you can’t see is any trace of hurricane force winds.
Not finding hurricane force winds at the eye, I looked at the other nearby stations as well. The weather station at Cape Hatteras is in the “dangerous semicircle”, the right hand side of the storm track (Fig. 2) where the speed of the storm is added to the speed of the winds circulating around the eye. Beaufort, on the other hand, is in the safer half of the storm, where the speed of the storm is subtracted from the circulating speed of the winds. The Onslow Buoy is also in the safer semicircle, on the left of the storm track in Figure 2. Figure 4 shows those records.
Figure 4. Winds at TS Irene landfall for Cape Lookout, Beaufort, Onslow Offshore Buoy, and Cape Hatteras.
As you can see, although Irene definitely qualifies as a solid tropical storm (winds greater than 35 knots), it does not reach or even really approach the 64-knot threshold for hurricanes. Other than at the eye itself, the winds did not exceed 50 knots, much less reach 64 knots.
After crossing over the land near Cape Hatteras, Irene headed back out to sea again. I thought perhaps it might have picked up steam when it went out over the ocean again. It made a second landfall in Atlantic City and went along the coast to New York.
Figure 5. Second landfall for Irene.The nearest stations to Irene’s track are Costeau (near Mystic Island above Atlantic City), NY Harbor Buoy (outside the mouth of the harbor, in the dangerous semicircle), Sandy Hook (hook shaped peninsula just above Long Branch and central hurricane symbol) and Kings Point (near New Rochelle above New York City). Note that the storm is claimed to be a hurricane until it gets well into New York State.
It appears from an examination of the station data shown below in Figure 6 that it did not pick up strength over the water. By the time Irene reached land a second time, it barely qualified as a tropical storm, much less a hurricane.
Figure 6. Wind speed from Tropical Storm Irene as it made the second landfall.
So, despite looking at Irene before, during, and after both landfalls, there is no hint of a hurricane anywhere. By the time it got to New York the eye of the storm had dissipated, what was left were huge bands of rain clouds.
Is there a moral in this story? Well, I can understand people taking extra precautions, better safe than sorry is a good rule. And I certainly imagine that when the Weather Service re-examines the records, the error will be corrected.
But that doesn’t help in making the decisions. As soon as Irene hit land, it should have been downgraded immediately to a tropical storm. That’s what it was, not a hurricane making landfall but a tropical storm. As far as I can tell, we still haven’t had a hurricane make landfall during Obama’s presidency, a historical oddity.
Individuals and city mayors and the people in charge of the emergency response can call for any level of reaction to storm threats. They may decide an exaggerated response is appropriate.
But they need accurate information to do that, not exaggerated claims. They need the actual facts, the best estimates with no exaggeration on either the high or low side.
In this case, it appears that people got so wrapped up in the question of the winds, and the fear of the winds, that they overlooked what actually made Irene unusual. This was not the wind speed, but the size of the storm. Combined with Irene’s generally slow movement over the ground, Irene’s huge dimensions meant that any given area would get rained on for a really, really long time.
And in turn that meant that the cities and towns along the coast, the ones receiving all of the attention from the fear of high winds and attendant storm surges, weren’t the towns in danger. Unlike the coastal cities, the vast expanses inland were not able to have the rainwater just flow back into the ocean. Inland, the water piled up and overflowed the banks.
And so, because of the overestimation of the wind speeds, our attention was diverted from the real threat. Because of the claimed hurricane-force winds, a storm surge up to eight feet was predicted in New York Harbor. But in the event, the storm surge was barely three feet, a non-event … and meanwhile, New England was getting badly flooded.
So the moral to me is, honesty is the best policy for a National Weather Service. Don’t exaggerate the possible effects to be on the “safe side”, don’t minimize the possible effects. Just give us the best information you have, and let us make up our own minds. As Sergeant Friday used to say … “Just the facts, ma’am” …
w.
NOTE: All wind data is from the NOAA National Buoy Data Center http://www.ndbc.noaa.gov/.
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Caleb says:
September 2, 2011 at 8:35 am
Yes, I have, it’s the disadvantage of a lifetime spent much at sea. Like Irene it was the end of a decaying hurricane, at sea somewhere north of Hawaii. Very low pressure (~950 mb) but the winds, although strong, never got much above 50 knots. Go figure. We had a recording aneroid barometer on board, it made a very shocking graph of the dip in pressure. Wind speed was measured with a hand-held anemometer and the Beaufort Scale.
w.
@ur momisugly Robert Smith
Yours was a Cat 2 defo
You must be up to Hurricane Mòrag by now 🙂
Yours
Dave the Yorkshireman
Willis Eschenbach says:
September 2, 2011 at 9:25 am
Another note on the Duck Pier question. Adjusted for height, that is 59 knots sustained, about 30% less power than the weakest hurricane.
There is also a NOAA station on Duck Pier. The maximum sustained wind measured at that station was 29.9 m/s, but that anemometer is also high (14.5 m). Adjusted for the height, that gives us 56 knots.
So no, according to the actual measured data, it wasn’t a hurricane at Duck Pier, or even close.
w.
Savethesharks said “Even though Irene’s winds were not as intense as they could have been, and you rightly so point out the lack of storm surge at Battery Park (even though I think the mb pressure was within the range of a category 2 as well),”
The surge was well to the right of the storm, around RI and the Cape. The surge does not depend on pressure but on wind-driven water.
Fine. Then 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.
Dr Science said “If there is some special category of hurricane that says “it’s a hurricane here, but the winds are over there” hurricane, then NHC needs to create a category for it.”
It’s called a hurricane. Measurements were taken at flight level and with radar and Irene was a 75 knot hurricane at landfall. Whether any winds of that speed are measured on land is of no consequence.
I told you guys in the Irene thread that the local NC stations were putting up “wind gusts” to make it look worse. And only one small section of the outter banks had any gusts over 74mph. This thing was not a hurricane at landfall. So our long streak of not being hit by a hurricane is still going….
Anyone taking a boat offshore from some of the islands of the Bahamas that have taken a battering would’ve been, er, brave. There’s a reason the forecast cones were developed, and that’s as zones for shipping to avoid based on typical track errors.
Are you really suggesting there weren’t any sustained hurricane-force winds from Irene at any time? The official storm report isn’t yet available from NHC, but it will contain all officially-recorded (and some unofficial/’amateur’-recorded) winds. Arthur’s Town on Cat Island recorded a gust of 143mph, but Googling hasn’t turned up the maximum sustained wind yet. Safe to say that the 1-minute average containing that 143mph gust will be somewhat more than 74mph.
While we wait for the wind gauge data, this looks like a bona fide hurricane to me:
http://www.sun-sentinel.com/media/photo/2011-08/281653160-24134155.jpg
Have a look yourself at the pictures of the damage caused in the Bahamas and the Turks & Caicos islands. Read the reports of homes completely swept away by storm surge, of roofs torn clean off homes and schools by the wind. Suggesting there was no hurricane in these areas just because the US reported winds don’t yet tally with the NHC real-time statements is beyond “trust but verify”; it’s illogical in the face of all available evidence.
Let’s be sensible about this. Willis has said that, based on the evidence thus far, he’s not convinced that Irene was a hurricane at US landfall, particularly that no hurricane-force winds were felt onshore. Fair enough, there’s been no wind gauges shown to have felt sustained Cat 1 winds in the US. That doesn’t mean it was never a hurricane. It sure as hell doesn’t mean it was never strong enough to not count in the season’s ACE index. The historic ACE trend, presented by Dr Maue in his paper only recently, is a clear sign that hurricanes are not getting stronger and more frequent, as prognosticated by the CAGW crowd. Let’s not discredit the measure by trying to fudge what gets included in it.
As I said earlier, the NHC prefer to be consistent from one bulletin to another until pretty certain of a strengthening/weakening trend. They kept Irene at Cat 1 based on the dropwindsonde data they had at the time (tend to have to do this over water, so nobody gets a bump on the head if one lands on them at 24mph). Post-storm review might well see Cat 1 status withdrawn at an earlier juncture than it was in real time, but the NHC were behaving consistently with their typical actions.
Media and government are the ones politicising the weather, and how. Don’t fall into the trap of going in the other direction of surreality, but just stick to the reasonable. Give ’em enough rope and enough time…
Eric (skeptic) says:
September 2, 2011 at 10:21 am
Cite? And how on earth are the wind speeds on land “of no consequence”?
w.
Trees acclimate to wind. Wind that is substantially higher than what they are strengthened to will fail. Additionally, the ground saturation softens the soil, allowing the root structure to be uprooted. Street ways and buidling create venturi effect, thus increasing the local velocity of wind.
Tropical storm Irene presented some local affects on winds far and above what many trees could withstand.
Willis, the key question is whether Irene made landfall as a hurricane, not what it was, not what it became or what happened on land. Here are three scenarios, the first one is not a hurricane making landfall, but 2 and 3 are:
1. An 85 mph hurricane brushes the NC coast causing no more than 50 mph sustained winds on any portion of the coast
2. An 85 mph hurricane gets close to the coast but the eye never makes landfall. However, a sustained wind of 75 is recorded somewhere on land.
3. An 85 mph hurricane goes ashore, although no sustained hurricane force winds are measured anywhere on land.
Roger Knights– Your suggestion that the NHC categorize storms for damage potential. is excellent. Where I live, ground saturation followed by high winds is a big factor in power outages. Likewise, when it rains gently for several days, followed by a heavy rain, we expect flooding.
WeatherUnderground already offers maps of “Storm Total Surface Rainfall Accumulation”.
Bob Tisdale says:
September 2, 2011 at 8:24 am
Willis: I’m not sure the ground-based wind speed readings are accurate or telling the whole story. We’ve all seen pictures of the downed trees and trees that have been topped. I don’t need the photos; I can look out the window. Yup, there’s one, and another… But there’s another phenomenon that isn’t being reported. The leaves that remain on the 100+ hickory, maple, oak and birch trees on my property have been shredded at heights above 20 feet. There’s hardly anything left of them.
——————
My response,
How hard is it to pick a leaf?
Willis,
I agree with your numbers for Duck. My general point was that the spotty anemometer locations measured some wind speeds that were getting pretty close to hurricane force (it would be interesting to know more of the specifics behind the Cedar Creek Ferry Station observing station and data). Perhaps they were in the correct locations to observe the maximum winds, perhaps not. But those surface obs, along with the other analyses/observations that NHC has at its disposal, will probably prove convincing enough for the NHC to ultimately conclude that Irene was a Cat 1 hurricane when it made landfall in NC.
Don’t get me wrong, as we were chasing the record for the longest time between U.S. hurricane landfalls, I was certainly interested in Irene being downgraded to a TC before landfall in order to keep the chase alive (I think we had to make it into late September to get the record). But, although I may wish otherwise, my gut is that Irene will retain its hurricane status, even in retrospective analysis by the NHC. And for what I know currently, I wouldn’t be in disagreement.
-Chip
Keith says:
September 2, 2011 at 10:26 am
I didn’t mean to rattle anyones cage. Just a simple question, what should we believe? The only data is from the NHC. Questions, questions, questions, credibility, Nanny, politics, etc.
Sorry to upset you.
Sincerely yours,
Willis: Just for the record, my wife and I sat out Irene on our 42 ft sailing catamaran at Sea Gate Marina, about 2 miles north of Beaufort, NC on the Intra-Coastal Waterway. Our on-board wind speed indicator recorded gusts of 75 knots, and sustained winds (over a period of 10-15 minutes) during the ‘backside’ of Irene, of 67 knots. There were sustained winds higher than that, but we dared not pop out and check the instruments when winds were that high. We survived handily, having two anchors buried in the earth, two more anchors out in the water fore and aft, and four lines (foreward, aft, and two springs) tied to the top 1 ft of the pilings of the docks (15 to 20 feet away). The pilings were completely submerged during the highest of the storm surge, about 7 feet for us.
Willis is correct to conclude that Irene was not a hurricane when it crossed over NC and thereafter. He’s nailed the windspeed measurement data. NHC/NOAA has been over-categorizing hurricanes since the 2003 season when I started reading all reports on every cyclone which could reach eastern FL, where I lived. They’re doing exactly the same thing today. Nothing has changed. In fact, many of the named forecasters identified are still on the job since the 2003 season. We don’t know why the upward danger bias exists. We are left with guessing. Irene is just the latest example of its existence and persistence. It would be of immense public benefit to all if NHC/NOAA would enter the dialog and explain why their forecasts appear to be overblown. They’ll never do that unless forced, meaning Congress. The controlling view of every unelected, jobs-for-life bureaucrat is that they owe no accountability to ordinary citizens. “We’re the experts; the public has no right to question our work product or examine our workpapers and data; and you can’t ever fire me”; is their bottom line. They know how the system works. They can pretty much do what they want; to hell with public opinion asking questions. But today is a different world with respect to the public’s unquestioned acceptance of government issued reports on anything, most particularly scientific subjects. The public is sick and tired of paying for these scary, fear inducing papers and the salary/benefits of employee/authors. This new healthy environment will ultimately percolate through changes in political leadership on down to bureaucrats producing biased reports or ducking accountability for reporting results. This process will take time. What can be done to improve NHC/NOAA’s hurricane reporting system in the meantime. Maybe nothing. But the entire hurricane reporting process could easily be improved if NHC so chose. First, the daily (6 hr) one-page reports are far too short, extremely cryptic, and conclusory. There is little or no technical detail supporting conclusions. These daily reports should be written by named teams, not an individual which appears to be the case. Different viewpoints within the team should be shown and discussed. Limitations on technology/data should be discussed. A much more comprehensive format is needed. NHC should avoid ‘steering the public’ with scare tactics to protect it from itself by over-blowing storms. Hopefully, this mentality is changeable. The public can and will protect itself if given realistic options for action. Don’t assume the public is stupid and can’t act in its self-interest.
No problem, no upset caused at all 🙂
As with all things, we should believe the observational data rather than modelled infilling, grandstanding politicians or ridiculously contortionist TV reporters. Let’s not assume that potential exaggeration at some times in some places means exaggeration everywhere at all times.
NHC may collate data and be the only ‘official’ presenters of it all, but there are other sources, particularly when storms are in non-US territorial waters,
@Joe Kirklin Bastardi
A friend and I followed your tweets as Irene passed over NC until it passed over us on Narragansett Bay.. On the evening of the 26th the friend wrote “shear winds and land, plan on picnic sunday, with beach umbrellas” and “what’s Bastardi saying now hahahaha” On Sunday he couldn’t write – no power. And no picnic.
Your power scale argument is compelling. Irene was unlike the hurricanes and tropical storms that we have endured. The wind strength was impressive but nor’easters often blow harder. Nonetheless we lived without power for 2 days and lost several trees.
I attribute the local damage to the size and duration of Irene. Over the course of 12+ hours through a high and a low tide the wind blew. It seemed constant, not gusty, as it slowly switched by 180 degrees. Every vulnerability was exploited.
Concerning the comments (on this blog and others) about the rain causing soft ground, I don’t believe that is what occured here. Trees fell, many limbs fell too. It rained a bit, but the level in my pool didn’t change much. A check of the rainfall records on the east side of Irene would likely disprove this theory.
The folks who are ignoring the impact of Irene reveal a disappointing willingness to use weather events in the (A)GW debate. In his blog Dr. Mass argues that our hurricane measurement tools are inadequate to make targeted hurricane forecasts similar to those in tornado alley. Here! Here! Then he goes on to suggest that Bloomberg’s decisions were politically motivated as opposed to prudent. Huh?!
Call Irene a hurricane, a tropical storm or a tomato sandwich. It’s immaterial. What matters is that the “hype” – the cable media’s 24/7 coverage, the 30 minute local news updates, and the NWS forecasts – caused us to prepare for a very powerful storm thereby preventing additional damage and saving lives.
Hurricane or not (OK not) Irene was classified by the BBC as “Climate Disruption”, the first time I have heard this latest appology for the non-appearance of Global Warming actually used in earnest by the BBC (BCC). I suspect that this is going to be the begining of a trend. By Christmas it will be used fifty times a week for every usual weather event across the world.
Watch this cooling space……
There seems to be a gale wind blowing where I live.Lighting and thunder! Gotta go secure the lawn chairrs. A representivive of BEER has arrived in an artic enxironment. Will be back next week if I survive.
Cheers
Eric (skeptic) says:
September 2, 2011 at 11:24 am
Not for me. For me the key question is, once it struck the land and was clearly not a hurricane, why it was still listed as a hurricane not only at landfall, but also when was crossing the land, as well as when it left the land and went back over the ocean, and when it made its second landfall in Atlantic City, and all the way to when it was still listed as a hurricane over New York City?
Riddle me that one, when the winds around New York barely made it to tropical storm strength (Figure 6).
w.
Chip Knappenberger says:
September 2, 2011 at 11:44 am
Thanks, though. They claimed Irene was a Cat 1 hurricane all the way to New York, so it seems there’s no telling what they will “ultimately conclude”
I still don’t get it, Chip. I thought the official definition of a hurricane was sustained surface winds of 64 knots. My understanding was that what you call “getting pretty close to hurricane force” has an official name. It’s called a “Tropical Storm”
I watched it minute by minute as it developed. As soon as it hit Carolina, the eye disappeared, the circular rotating shape broke up, and it became bands of storm activity. I thought “Well, Irene’s a tropical storm now”, and I waited for the announcement. No announcement. Woke up the next morning, they’re still calling it a hurricane?!?
But it kept on and on, with bulletin after bulletin from the NHC calling Irene a hurricane … I figured, well, maybe my eyeball estimates are wrong and that is a hurricane. It wasn’t until several days later that I started actually investigating it and … well, it looks like my reading of the satellite pictures was quite accurate.
I love it. A storm passes over a stretch of the US coastline with more anemometers per mile than likely any other part of the US coast. Not one single anemometer registers it as a hurricane, even looking at it minute by minute.
And you insist that it made landfall as a hurricane? For me, making landfall as a hurricane means that hurricane strength winds are recorded, not from planes or buoys or ships (or models), but from the land. Am I missing something? Is your understanding something different?
Finally, Chip, for me the point is not whether it made landfall as a hurricane. I’m not chasing any records. As I said in my post above:
Foolish me, I expected the NHC folks to be watching the reports, minute by minute, from the anemometers all along the coast. And when it wasn’t a hurricane anywhere, I expected them to say “IRENE has been down-graded to a tropical storm. Flooding is the main danger of a tropical storm. The ground has been weakened by heavy rains, so many trees will fall, taking down power and phone lines”.
In other words, I don’t want them playing it safe. I want them playing it honest. I don’t want to have to value NHC information at a 30% discount for inflation. I want it to reflect the actual reality on the ground.
Thanks for your thoughts,
w.
Keith says:
September 2, 2011 at 12:30 pm
You wanna artic beer for the holiday? It’s on me. Have a good weekend!
Cheers
Eric (skeptic) says:
September 2, 2011 at 10:16 am
Savethesharks said “Even though Irene’s winds were not as intense as they could have been, and you rightly so point out the lack of storm surge at Battery Park (even though I think the mb pressure was within the range of a category 2 as well),”
The surge was well to the right of the storm, around RI and the Cape. The surge does not depend on pressure but on wind-driven water.
============================
Well actually, its both.
In intense hurricanes, the sudden storm surge comes from the “dome” of water in and around the eyewall, in the areas of exceedingly low barometric pressure at the center of the cyclone, and of course around where the strongest winds are screaming and piling up that water.
So the very low pressure at the center, and the intense winds that are caused by the pressure differences, rushing toward the center of the cyclone, both help raise the deadly dome of seawater and when it comes ashore.
But in a hybrid storm like Irene, who had really lost many tropical characteristics by the time she got to NE in that broad right front quadrant, certainly the surge had moved away from the center as she unraveled and her central pressure began to climb, and of course that long fetch of strong winds helped pile up the water dramatically on her east side, not unlike a nor’easter.
Not a true storm “surge” in the technical sense like you would see in a tightly wound truly tropical cyclone, like Katrina, but a damaging surge nonetheless.
Chris
Norfolk, VA, USA