How forecasters develop hurricanes' 'cone of uncertainty'
This is the National Hurricane Center's forecast track for Hurricane Irene, released at 5 p.m. Wednesday.
August 24th, 2011
10:05 PM ET

How forecasters develop hurricanes' 'cone of uncertainty'

It sounds like something out of the Austin Power movies or Robert DeNiro’s “circle of trust” in the Focker movies, but in the world of hurricanes the “Cone of Uncertainty” is just that; as the forecast goes out in time, the exact location of the hurricane becomes less certain.  Therefore the official forecast from the National Hurricane Center paints an area around the expected track to reflect the average error of the forecast.

You'll see the cone in the image above. The image shows the National Hurricane Center's prediction, as of 5 p.m. Wednesday, of where the hurricane could go over the next three days. The "cone of uncertainty," representing a range where forecasters think the hurricane's center could go, is in white.

The hurricane center, located near Miami, is tasked by the National Weather Service and the National Oceanic and Atmospheric Administration to constantly watch the tropics and warn when tropical waves and disturbances grow into organized low-pressure areas known as tropical depressions. When tropical depressions develop, the hurricane center starts issuing advisories on the system.

Sophisticated models running on some of the fastest computers in the world ingest data from satellites, ship reports, radar (if it is available), and data from weather balloons, airplanes and weather stations. Literally billions of calculations are done with very complex equations to help model the atmosphere into the future. More than 20 different kinds of models are run - some being more reliable and complex than others - to help forecast the track and intensity of the storm. You may have seen one of our meteorologists show the "spaghetti" maps on television depicting a storm's possible paths, or seen the plot maps on cnn.com/hurricane.

Example of plots:

Forecasters use this model data - along with real-time information obtained by satellite, radar, observation and hurricane hunter planes that fly right into the center of the storm - to help the hurricane center issue an official forecast track. That forecast track, issued every six hours, shows where the storm is expected to go over the next five days and how strong the storm may be.

Even I, as a meteorologist, know that weather forecasts are far from perfect. The hurricane center, which keeps records of every track it issues, is aware of that fact as well. The hurricane center figures out what its average error is at various forecast horizons - 12 hours, 24 hours, 48 hours, etc. - to help it generate the “cone of uncertainty” on its forecast track (the white area on the map).

The cone basically shows that the center's 12-hour forecast position is, on average, 36 miles off. At 48 hours, it is around 100 miles off.

So, let's say that I live in City X, and the storm is forecast to pass 100 miles to the south of me two days from now. I have nothing to worry about, right? Wrong. Because the average error at 48 hours is 100 miles, the storm could be right over me in two days.

This is why meteorologists and emergency managers will constantly preach not to look at the line on the forecast track, but to look at the "cone." If you are inside that area, you could end up in the direct path of the storm.

Because the atmosphere is so complex, errors from a particular forecast become larger over time. So the cone is much smaller at 12 hours than at five days out, because we know that on average, our short-term forecasts are much better.

So as Hurricane Irene approaches, remember not to focus on that line you see on the forecast track maps. Instead, look at the “cone of uncertainty." In the end, the storm may go anywhere in that area.

soundoff (59 Responses)
  1. Lock

    Every Hurricane should not be treated like the next Katrina. The people near the coast have the money to leave and replace thier property damage, unlike those in Lousiana. The only people in real danger in NC are the poor and those in rural areas, who will naturally be the last Emergency Responders will address and can't leave. Yes, plenty of old and poor people in NC don't have cars and buses don't run. If you are trapped in your house or condo at Naggs Head, Hatterous, Myrtle Beach, etc , well 200 of your neighbors will find you the next day and EMS crews will come in mass to your assistance, but if you live in twitalyoursack NC/SC well you better hope your sisters boy comes looking for you on his fourwheeler, with a chainsaw or else you better start nawing on that tree accross your chest like a beaver because its going to be at least 3 weeks before they find your body. In the south, you take care of your own!

    August 25, 2011 at 9:05 am | Report abuse |
    • CD

      It's pretty ignorant thinking that everyone along the coast is rich. I'm not far from the coast and surrounded by poor communities – but it's easy to cast stereotypes around from far away. I live in a low-income town in the path of this hurricane, and the houses are relatively far apart.

      Way to be a moron.

      August 25, 2011 at 9:30 am | Report abuse |
    • Fred

      You're right on one front, anyway. Every hurricane is NOT like Katrina 2005, and most won't even be close. Reason for that is because a good portion of the damage to N.O. was the result of the levies being breached – not likely to happen in other hurricane-prone cities. Wealthy, poor, whatever status doesn't matter much when one lives in a bowl 50' below sea level!

      The "south" is not the only area of this country that takes care of its own. Tell that to the folks in Joplin, MO or Minot, ND or any other area recently flooded, "tornadoed", or even "earthquaked". Is it possible for you to think outside of your own county? *shaking head*

      August 25, 2011 at 10:36 am | Report abuse |
    • Wendy

      Fred...N.O got the press because of the water. The Damage from Katrina was from Florida to Texas, but those people were forgotten because people chose to focus on N.O. Bottom line, I to have lived in Florida my whole life and aside from the "idiot" above to likes to call herself one, most of the older FL homes were built to withstand huricanes (flat roofs, stucco and tile). One thing you need to live by, if you are told to evacuate, then do it. the people who stayed behind in New Orleans, Florida, Mississippi, and Alabama made thier choice and increased their suffering. I promise you, even before Katrina, if you are staring down the eye of a CAT 4 or 5, you leave, period, there is not one possession in my house worth living through that kind of he!!.

      August 25, 2011 at 12:05 pm | Report abuse |
    • Nesto

      Very stupid thing to say. There are plenty of people that live on Long Island that CANNOT afford this storm. I don't know where this misconception that everyone that lives in the coastal region is upper middle to rich came from. Certainly not based anywhere in fact. This also isn't like other areas that can easily evacuate, so the majority of us have to ride this out and deal with the flooding...which is what I am most worried about.

      August 25, 2011 at 4:47 pm | Report abuse |
  2. kardiac

    Thanks Jethro for today's lesson in "Wingnut Thinkin'"

    August 25, 2011 at 9:24 am | Report abuse |
  3. CD

    That's why this article is called "Cone of UNCERTAINTY".

    But reading comprehensions seems to be low on the list of priorities for nutjobs.

    August 25, 2011 at 9:31 am | Report abuse |
  4. Randy

    Hey dopey.... it's spelled "Charlotte". It's amazing how many people sit through hours of school and do not learn basic grammar or spelling.

    August 25, 2011 at 9:39 am | Report abuse |
  5. Uggggggh

    I find myself conflicted. While I do not want to defend an obviously rightwing teatard zealot I feel compelled to put it out there. I believe he knows it is spelled Charlotte but his accusations of them being greedy people there and thugs prompted the charloot spelling, char-loot

    August 25, 2011 at 9:49 am | Report abuse |
  6. Nikolas

    The chart is only the product of centuries of meteorological observation. The cone of uncertainty doesn't, btw, say the hurricane will not hit Charlotte, NC, only that it's statistically insignificant; however, in the improbable event it reaches that far inland, without a large body of water to power it, it would most likely downgrade from Hurricane to "tropical storm" and might cause some minor water damage to homes with bad weatherproofing. As far as that earthquake goes, it hardly seems like something "The man upstairs" would waste time on. It's not the most corrupt time in American history. Besides, as far as affairs of state go, "Give unto Caesar that which is Caesar's. We aren't being tested, Earth is behaving in the way it has behaved for the whole of recorded history, through well-understood processes. When good things happen to good people and bad to bad, you say, "they are getting what they deserve." But when bad to good or good to bad, you say, "our Lord is testing us." If your going to observe christian faith, you should accept that in earthly matters sometimes things just happen (even big things) without intent, understand that judgment comes in the end, and understand other foundations of faith, such as the parable of the prodigal son, and the parable of the workers in the vineyard. Christians who obsess themselves with old testament wrath and apocalyptic revelations make Christians look bad. If your going to be a Christian, do so in the example of Christ. If you practice some other faith, then still do so in a way that doesn't compromise your humanity, and if you are agnostic or atheistic, just be kind and responsible. Basically: weather happens, don't attribute every event to God teaching people lessons.

    August 25, 2011 at 10:02 am | Report abuse |
  7. Uggggggh

    I was born and raised in coastal Florida. I have been through to many hurricanes and tropical storms to count (yes I can count past ten even though I am a Flor-idiot, I just take off my socks and shoes) and hurricanes generally hit within those ranges but not always. Remember 2004 with the 4 storms back to back to back to back essentially? Remember Charlie hit central Florida twice, it came Gulf side across the state went into the Atlantic did a freaking 180 turned around and hit us again, pretty sure it was Charlie, they all blend together at this point.

    August 25, 2011 at 10:09 am | Report abuse |
  8. Mel Q

    Yes it is obvious that you comprehend the article. And it is apparent that you have not learned much in church either.

    August 25, 2011 at 10:32 am | Report abuse |
  9. rtbrno65

    I can't wait until the cone of uncertainty gets licked.

    August 25, 2011 at 10:48 am | Report abuse |
    • Floyd from Ilinois

      I scream at that awful pun.

      August 25, 2011 at 4:33 pm | Report abuse |
  10. wil123

    I was watching the weather channel last night and had to laugh when they forecast the track and stated no matter which track is taken it is going to be bad for the NE, Come on- typical. remember the worst they make it sound the more people watch the more revenue and it just so happens home depot is a major sponsor. I am not saying you shouldn't have some concern but don't subscribe to the panic that they instill with there dire predictions.

    August 25, 2011 at 10:50 am | Report abuse |
    • Public

      yeah, I'd agree. They want people to watch their channel versus their local news, but the local news is probably scaring people even more than the weather channel is..

      August 26, 2011 at 10:12 am | Report abuse |
  11. Michelle

    I don't know why anyone would keep bringing up Katrina and compare this to it. Yes, a hurricane no matter the size can be bad. It doesn't depend on the Category of the hurricane necessarily. It can depend on where you live and how they're ready for it. Also the storm surge is the worse part. I live in Norfolk, VA and am in a flood zone near carrier piers. so if this hits, I'm out of here....or else I'll be paddling down the road in a canoe. As a former AG (Weather forecaster) for the Navy, I know that weather can only be predicted somewhat accurately within 24-36 hours. Any further out than that, you're just guessing what will happen next. That's why it's a "prediction". Don't blame the meteorologists for doing their jobs. Mother Nature does her own thing.
    And as for Katrina...yes the storm itself was massive, obviously. but maybe New Orleans would have been somewhat ok if the levees held. Then again, maybe the idiots in New Orleans should have just all packed up and left for good. I know there's hundreds of years in history there and I like the city too, but maybe Mother Nature is trying to tell you all something.

    August 25, 2011 at 10:55 am | Report abuse |
    • Wendy

      Agreed Michelle! I mean really, how can you sand at the base of a 25 foot wall with Lake Pontchartrain on the other side and think "this is a good place to build a home".

      August 25, 2011 at 12:08 pm | Report abuse |
  12. Nikolas

    @MelQ: @ me???? I pay all sorts of attention in church, and not just to people fidgeting in the pews and paint scuffs on the wall! I even listen to the readings and the sermons and such. My congregation just focuses more on living in christian fellowship than on political punditry and explaining the weather.

    August 25, 2011 at 11:02 am | Report abuse |
  13. R. Burgan

    I'm always amazed at the poor quality of the hurricane data and graphics available in the U.S. from various sources. The quality of the information has a lot to do with how much people trust it. Compare what you see from the National Hurricane Center with that provided by the Joint Typhoon Warning Center (U.S. Military) and you will see what I mean. The JTWC website is http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/ Also, a great website for Typhoon information is: http://www.typhoon2000.ph

    August 25, 2011 at 11:10 am | Report abuse |
  14. Hieda

    You guys are brutal...

    August 25, 2011 at 11:11 am | Report abuse |
  15. Jack Be Humble

    I'm pretty sure Char'loot' was a play on words, in reference to the 'money grubbing' referenced by the original poster.

    August 25, 2011 at 11:38 am | Report abuse |
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