Average 20 year old weather nerd. Plymouth State University Meteorology, Class of 2018. NOAA Hollings scholar. Summer 2016 intern at NWS Boston.
By: MAweatherboy1, 11:45 PM GMT on October 08, 2016
It seems the popular hurricane conspiracy this year has become “The NHC is overhyping the storms’ winds.” By now you've probably heard about what happened a couple days ago, when a notorious political commentator delivered remarks on Hurricane Matthew's wind speed being overstated. The supposed basis for such claims is a lack of ground-truth verification once the storm is onshore. The idea that the NHC is intentionally overstating wind intensity is largely based out of ignorance. People like Matt Drudge believe that the NHC has a “monopoly on data” that allows them to basically say whatever they want about a storm’s intensity. These ideas are nothing more than off-base conspiracy theories, and primarily from a particularly anti-science wing of the political right. Today I’ll go deeper into debunking this conspiracy, and hopefully give a clearer idea of what is really meant when officials describe the “winds” of a hurricane.
It’s fair enough, when confronted by the claims of Drudge and others, to say that they’re full of crap and call it a day. It’s certainly a true statement. But for me, this is a subject worth going deeper into. Let’s start with what’s meant by a storm’s “winds”. When the NHC reports wind speed in an advisory, the winds reported are the maximum 1-minute sustained winds. So often, practically always, the media will simply report, for example, “Matthew has 140mph winds”. This gives the impression that the entire storm is producing these winds for dozens of miles in any direction. That couldn’t be further from the truth. In reality, these maximum winds tend to be confined to a very small portion of the hurricane, usually in the northeast quadrant of the eyewall. These are the winds that the NHC reports, however, and that is the way it has always been done.
The maximum wind speeds for a storm like Matthew don’t get pulled out of thin air. For a hurricane over open waters that isn’t affecting land, there is definitely a degree of uncertainty any time maximum winds are analyzed via the Dvorak technique, and that is accepted and not seen as a problem since the storm isn’t a threat to land. Storms like Matthew are different. Thanks to the men and women on the flight crews of the NOAA and Air Force hurricane hunters, we have had near constant direct measurement of Matthew since before it was even a named storm. Using multiple techniques, these flight crews are able to derive a storm’s wind strength and other characteristics like the shape of the wind field. These measurements come with a low degree of uncertainty; they may not be perfectly precise, but they are real measurements and provide a legitimate best metric of real time storm intensity. Once again, aircraft measurements are the way hurricane monitoring has been done for a long time.
So why do the winds reported by aircraft crews rarely get translated into measurements on the ground during landfall? My explanation so far provides part of the answer, but there’s much more to it. Chiefly is the availability of on-the-ground measurements. When a storm’s highest wind speeds and gusts are reported, those values usually come from either NWS ASOS/AWOS sites, or personal weather stations, the latter of which can be of dubious accuracy depending on siting and equipment, especially where wind data is concerned. If we focus only on the more official measuring equipment, the disparity in what the ASOS systems measure versus what the aircraft crews measure can be explained pretty easily. ASOS systems are fixed platforms, and there aren’t a whole lot of them when considering how big a hurricane is. For them to be of any use, the storm has to come to them. The hurricane hunters can go to the storm. The hurricane hunters are aiming to find the highest winds, while the stations on the ground are left with whatever the storm’s track gives them. Based on this, it is very difficult to get a weather station exactly in position of a maximum wind radius that may occur over only a single square mile of space.
There are other factors as well that explain some of the difference. Friction from the land surfaces acts to slow down winds somewhat. Aircraft measurements are usually taken over the ocean, where friction is far less. In addition, hurricanes as we know are ocean-going features and will weaken rapidly if brought over land, so a surface station inland by more than 15-20 miles stands a dramatically reduced chance of seeing the maximum sustained winds. Inland areas also deal with trees and buildings that block wind flow. The reason coastlines tend to be windiest places during hurricanes is that they are the land surfaces that most minimize all these issues. They are the boundary between land and ocean, the first places onshore to feel the winds, and they are free of obstructions, so they get those winds in their fiercest, un-moderated form.
Looking specifically at Matthew, what were the most important factors among what I’ve discussed that caused its lack of on-the-ground verification of its maximum winds? For this storm, it was all about track. Like most major hurricanes, Matthew’s maximum winds were in the storm’s northeast quadrant. That area was crisscrossed dozens of times over by hurricane hunter planes in the past week. But it never touched the shores of the US, not until it happened today in a dramatically weakened form, with the storm barely at hurricane intensity. The bigger surprise would’ve been if any land station in the US had recorded sustained winds in the 120-130mph range that the storm was at as it passed by the Florida coast. As I said on the blog this morning, the US was very lucky, Florida in particular. A 40 mile shift west in track would have led to devastating wind damage. Hurricanes are multi-faceted beasts, however, and we’re seeing today that Matthew’s biggest hit on the US will be from inland fresh water flooding, not wind or even coastal surge.
There was one major land mass that experienced Matthew’s right front quadrant; the country of Haiti. One of the world’s poorest countries, Haiti was struck by Matthew at near peak intensity. Nearly 1,000 people have been confirmed dead, with some towns almost entirely wiped out. Of course, in Haiti, there is practically nothing in the way of ground truth weather reports. But I’m sure anyone lucky enough to survive the eyewall passage there would vouch on their life that they experiences sustained winds of category 4 intensity.
As with any hurricane, we will never know what the highest wind gust on land was with Matthew, in Haiti or the US. For that we would need measuring equipment at every spot on Earth. But to claim Matthew’s wind was somehow “overhyped” is more than absurd. It’s an insult to the people of Haiti, Cuba, and the Bahamas who experienced it firsthand. It’s an insult to the crews of the hurricane hunter planes risking their lives to provide us with such valuable data. And it’s an insult to all of the hard working meteorologists at the National Hurricane Center, numerous local NWS offices, and within the private industry who are doing everything in their power to issue warnings and guide decision making based on the real-time reports from the hurricane hunters.
There are a couple of lessons that can come out of this. One is the evermore apparent obsoleteness of the Saffir Simpson Scale. As we’ve seen today, hurricanes are so much more than a wind speed number. Classifying a storm hundreds of miles in diameter based entirely on a wind speed value over a couple of miles distance is not only a poor representation. It’s downright unsafe, and way too many lives have been lost because of it. A tornado can be classified by its winds. A hurricane cannot. It is absolutely essential that a new, objective scale be defined that classifies hurricanes based on more than wind. It should take into account a representative wind value, for example, some weighted average of the absolute maximum sustained wind, which we use now, but also the average diameter of the 50 and 64kt wind radii, and in what we now call major hurricanes an average of winds within 20 or so miles of the center. Surge and rainfall potential would also have to be considered, taking into account storm size and motion. A scale like this would likely require years of development and experimental testing. It would involve a reanalysis of past storms and an application to future ones. The wait has been long enough, however. It’s time to act. Unfortunately, it’s likely this call will fall on deaf ears, and we will continue to classify multi-dimensional storms in an entirely one-dimensional manner.
Another lesson is that continued improvement is needed in the communication of meteorological hazards. It’s clear we haven’t yet reached the point where the message the NWS communicates gets communicated as desired. This is due to a combination of poor meteorological understanding on the part of the general public, as well as a ratings driven media that neglects to cover a storm like Matthew in lieu of the election cycle until it is right on top of us, and when they do cover it they will only do so in a way that almost inevitably involves hype, especially the national media. A storm like Matthew deserves to be taken and talked about seriously. There is a right way and a wrong way to present the threat, however, and too often the facts are glossed over in favor of the headlines. Words. “Catastrophic.” “Unprecedented.” “Millions told to evacuate.” Okay. But why is it potentially catastrophic, why unprecedented, why should you evacuate when in the path? Much as the Saffir Simpson Scale issue is a scientific enigma, this communication gap is by far the more difficult problem to solve. There are so many sources of weather information now. It has turned into a genuine quagmire. What to believe, how to react. My advice to the general public is very simple: Trust the word of the NHC, your local NWS, and your emergency managers. Their job is to keep you safe, and they are very good at it. Listen to them. And whatever you do, do not listen to the likes of Matt Drudge. You can get your politics from him if you must, but not life-and-death advice. I’m sure there is more that can be done, but that is not my expertise, and I leave it to others in the field, especially those in broadcast and others on the front line of meteorological communication, to better serve those in harm’s way with the most accurate, factual information possible.
For anyone who made it through this lengthy editorial, your reading is appreciated. The primary purpose of this post was specifically to objectively debunk the conspiracy theory that the NHC is overstating maximum wind speeds of hurricanes like Matthew. The moral of that story is that a hurricane’s maximum sustained winds will always affect a limited area of land, and usually a limited number of people, and the odds of such winds actually being measured by a land-based weather station are very small. I wanted to throw in a few personal thoughts and suggestions at the end as well. As always, feel free to leave comments/questions. I’ve got quite a bit going on in my life right now, but it’s a lot of good stuff. I’m pretty busy most of the time, but it’s all in an effort to further my very young career in this field. I’ll keep you posted as time goes on and look forward to continuing to watch the remainder of this hurricane season, which is certainly not over. Enjoy the rest of your weekend!
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.