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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Jason ( the extremeone ) says:
September 3, 2011 at 3:33 pm
Jason, I don’t think a single person missed that point, much less everyone … but that wasn’t the point under discussion.
The question at issue was that calling a storm a hurricane when it isn’t one interferes with a proper analysis of, and response to, the threat from the storm.
w.
Re Roger Knights: I’ve read critics saying that, at a minimum, shutting down the bus lines as extensively as he did, and as early as he did, was extreme.
and Willis: Manhattan did over-react to the danger.
I have considered the point whether they overreacted to the point of shutting down the bus lines. I want to point out that bus lines are composed of busses driven by people who mostly have families that live in the area. These are families that must prepare their homes for the storms, whether it be evacuate, reduce the potential damage, and prepare for some temporary flooding and possible long term power outage. It is reasonable to expect to run even a weekend schedule? If you can’t mantain any kind of schedule, should you say, “Some busses will still run, but don’t be surprised if the wait is long.”?
From the point of making decisions, I think NYC made the right call 24 and 12 hrs prior to the storm. Transporation systems are people, who sometimes need to be with their families.
Stephen Rasey says:
September 8, 2011 at 9:18 pm
Stephen, thanks for your thoughts, Did NYC make the right call? To me, that’s not the issue.
The issue is that to make good decisions, we need good information. Not inflated information. Accurate information. NYC officials did not have that information.
With the weather service saying that there were hurricane force winds, New York had to consider the forecast storm surge of up to eight feet. The NYC harbor amplifies any storm surge because of its funnel shape.
But there were no hurricane force winds measured anywhere in the Carolinas where the storm struck, and by the time the storm hit New York, it barely qualified as a tropical storm. And as with most tropical storms, the real danger was not the wind. It is the rain causing flooding, particularly inland. On the coast, the water can just run back into the sea, but inland, large watersheds can cause extensive flooding in river valleys.
However, New York City hardly flooded at all. Why? Because for NYC, the danger was not the rain, it was the (erroneously forecast) storm surge. In the event, the storm surge was barely three feet, which did not flood NYC in any significant manner. The buses and the subways could have run quite happily. Meanwhile, in other areas further from the ocean where the rains could not just run back into the sea, there was extensive flooding.
Finally, while I sympathize with those people whose jobs call them away from their homes in times of inclement weather or other widespread problems (policemen, firemen, first responders, public transportation personnel, emergency management teams, military, Coast Guard, water rescue specialists, and the like), by the nature of their jobs sometimes they don’t get to say “big storm around, sorry, I want to stay home today”. If they need to “prepare their homes for the storms, whether it be evacuate, reduce the potential damage, and prepare for some temporary flooding and possible long term power outage” as you reasonably point out, it should have been done long before the storm hits. Joe Public has an excuse for not being prepared, but those folks have to expect that they may have to work in times of bad weather, power outages, or other emergencies.
w.
Willis Eschenbach says:
September 10, 2011 at 4:39 pm
“Joe Public has an excuse for not being prepared,…….”
========
Since when ?
What is your excuse when at sea, do you look to others to save your butt ?
I’m sure i’m missing something, but what happened to personal responsibility.
I have enjoyed reading the comments and the beginning discussion. Having a science background, I am concerned the NHC may not be stating “just the facts”. That said, I live on the southern NC OBX and have a couple of observations: I am NOT a meterologist – but living here have a vested interest.
1) We did not prepare for, expect, or realize a hurricane type wind event. We did prepare for a cat 3 or 4 storm surge. Here the storm surge was a non-event. To our west and north the storm surge was worse than storms in the last 50 to 100 years, as observed by local residents depending on the area.
2) The wind blew for 24hrs . Hurricanes in recent history blow for a few hours, which has nothing to do with categorization but a lot to do with reality. The back side of this storm had wind as strong or stronger than the front NE side, shortly after landfall.. Whether Cat 1 or Tropical Storm, the duration was significant here. The storm had a very large size.
Barometric pressure seems a more reasonable measure of storm cat than observed wind speed in my limited experience. Irene was significant in eastern NC. It appeared to be a non-event north of NC, other than the tropical storm type rain.
I did not see a reponse to the couple anchored on the cat sailboat, who appeared to have observed significant wind speeds and similar conditions to me. Any reason?