WHAT THE NHC ERROR CONE MEANS

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Alyono
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WHAT THE NHC ERROR CONE MEANS

#1 Postby Alyono » Fri Sep 30, 2016 10:08 pm

Mods, I believe this should be stickyied as this is VERY IMPORTANT


There are numerous myths regarding the cone. The two most common are

1. This is the area in which the storm could move. The cone represents the uncertainty
2. The cone is the area where impacts are expected.

Neither of these is correct. The cone is merely the 66th percentile based upon errors in the last 5 years. It in no way tells any information related to the true forecast uncertainty. In addition, it has nothing to do with the impact area as impacts often extend well away from the cone

Please remember this when discussing if an area is within the cone for Matthew. The actual uncertainty may represent an area larger or smaller than the size of the cone. Do NOT use the cone for any decision making processes
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Re: What the Cone Means

#2 Postby wxman57 » Tue Oct 04, 2016 6:26 pm

Many people (most?) have no clue what the cone really means. I keep seeing comments like "the NHC is going to move the cone" this way or that. The NHC doesn't move the cone. The identical cone is always there, no matter how much uncertainty exists. We definitely need to get rid of the cone and use something that would indicate true uncertainty in the track, or that would indicate true potential impacts (like a probability of wind impact). Such a "cone" might change shape with each advisory, depending on current uncertainty. It could be bifurcated (indicating two possible tracks) at times if it is based on models.
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Re: What the Cone Means

#3 Postby panamatropicwatch » Tue Oct 04, 2016 6:43 pm

From the NHC:

Definition of the NHC Track Forecast Cone

Definition:
The cone represents the probable track of the center of a tropical cyclone, and is formed by enclosing the area swept out by a set of circles (not shown) along the forecast track (at 12, 24, 36 hours, etc). The size of each circle is set so that two-thirds of historical official forecast errors over a 5-year sample fall within the circle. The circle radii defining the cones in 2016 for the Atlantic and eastern North Pacific basins are given in the table below.
One can also examine historical tracks to determine how often the entire 5-day path of a cyclone remains completely within the area of the cone. This is a different perspective that ignores most timing errors. For example, a storm moving very slowly but in the expected direction would still be within the area of the cone, even though the track forecast error could be very large. Based on forecasts over the previous 5 years, the entire track of the tropical cyclone can be expected to remain within the cone roughly 60-70% of the time.
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Re: What the Cone Means

#4 Postby HurricaneBelle » Tue Oct 04, 2016 7:36 pm

wxman57 wrote:We definitely need to get rid of the cone and use something that would indicate true uncertainty in the track, or that would indicate true potential impacts (like a probability of wind impact).


Agreed 100%. I basically cringe whenever I see someone mention the cone as if being "in" or "out" of it has any practical meaning for what conditions they can expect.

But as for "probably of wind impact", the NHC puts out a graphic for this. The problem is it's (relatively) buried on their site. This is the only "cone" people need:

Image

(Note: I'm "hotlinking" this image since whatever the current graphic on Matthew is at the time is the appropriate one to display.)
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Re: What the Cone Means

#5 Postby Alyono » Tue Oct 11, 2016 7:44 pm

The NHC PWI is better. However, it has the same issue as the cone given that it is based upon the deterministic forecast. It does not say anything about true uncertainty. It is still based off of historical errors.

I am working on a solution to this issue. However, the solution will likely not be available for free
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Re: What the Cone Means

#6 Postby mitchell » Tue Apr 18, 2017 9:08 am

Improvements in accuracy:

To arrive at the size of the cone, NHC's own track forecast errors are averaged over the previous five seasons at each forecast lead time: 12, 24, 36, 48, 72, 96, and 120 hours.

Image
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Re: What the Cone Means

#7 Postby wxman57 » Tue Apr 18, 2017 4:33 pm

panamatropicwatch wrote:From the NHC:

Definition of the NHC Track Forecast Cone

Definition:
The cone represents the probable track of the center of a tropical cyclone, and is formed by enclosing the area swept out by a set of circles (not shown) along the forecast track (at 12, 24, 36 hours, etc). The size of each circle is set so that two-thirds of historical official forecast errors over a 5-year sample fall within the circle. The circle radii defining the cones in 2016 for the Atlantic and eastern North Pacific basins are given in the table below.
One can also examine historical tracks to determine how often the entire 5-day path of a cyclone remains completely within the area of the cone. This is a different perspective that ignores most timing errors. For example, a storm moving very slowly but in the expected direction would still be within the area of the cone, even though the track forecast error could be very large. Based on forecasts over the previous 5 years, the entire track of the tropical cyclone can be expected to remain within the cone roughly 60-70% of the time.


The problem is, the cone doesn't really represent the probable track based upon CURRENT uncertainty. The current track uncertainty could be far greater (like Joaquin) than the average error over the past 5 seasons. And, of course, the cone, as it's drawn now, is currently shrinking each year. This means that more and more of a hurricane's impacts are being felt well outside the cone. Clearly, there needs to be a better way to visualize uncertainty based on current steering patterns (ensembles).
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Re: What the Cone Means

#8 Postby bamajammer4eva » Sun Apr 23, 2017 4:18 am

wxman57 wrote:
panamatropicwatch wrote:From the NHC:


The problem is, the cone doesn't really represent the probable track based upon CURRENT uncertainty. The current track uncertainty could be far greater (like Joaquin) than the average error over the past 5 seasons. And, of course, the cone, as it's drawn now, is currently shrinking each year. This means that more and more of a hurricane's impacts are being felt well outside the cone. Clearly, there needs to be a better way to visualize uncertainty based on current steering patterns (ensembles).


Agreed-Cone is looked at way too closely. TWC uses it etc

Excellent example of where Hurricane conditions were expected WELL outside of the cone and very near landfall! One must look deeper than the cone for their safety and the NHC should do something about this because TWC and everybody else uses the cone!!!

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Re: What the Cone Means

#9 Postby Kazmit » Sun Apr 23, 2017 8:50 am

New for this season, the NHC's "standard" cone now includes the wind field of the storm. Note how much wider the wind field is than the cone itself, which shows how being outside of the cone DOES NOT mean the storm's winds will not affect you.

Image
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Re: What the Cone Means

#10 Postby Alyono » Sun Apr 23, 2017 1:01 pm

Those wind graphics still do not display the risk area of winds. It does say the areas that are forecast to receive impacts, which is an improvement for sure.

However, to display the risk of impacts, you need a dynamic wind speed probability product, which NHC still does not have. The one I am creating is still in development
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Re: What the Cone Means

#11 Postby Alyono » Tue Jun 20, 2017 10:49 am

We need a reminder about what the cone means
THE CONE DOES NOT SHOW THE FORECAST UNCERTAINTY NOR DOES IT SHOW THE AREA THAT WILL BE AFFECTED

The cone is strictly historical errors. Nothing more than that. Far too many people continue to misuse the cone
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Re: What the Cone Means

#12 Postby gailwarning » Tue Sep 19, 2017 8:56 pm

Alyono wrote:We need a reminder about what the cone means
THE CONE DOES NOT SHOW THE FORECAST UNCERTAINTY NOR DOES IT SHOW THE AREA THAT WILL BE AFFECTED

The cone is strictly historical errors. Nothing more than that. Far too many people continue to misuse the cone


Thank you for explaining this. You and other professionals would be doing a great public service if you could write this in terms that the average person can understand and then start to get the word out. Maybe local Mets and emergency management groups could be a place to start. As simply an interested member of the public, I would certainly share any such explanation on my FB page. I hear far too many people in FL right now saying "we're out of the cone," and believing it's absolute fact because that cone is quite a distance from the state at the moment. That could be correct, but not for the reasons they think. It's still prudent for people to pay attention.
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Re: What the Cone Means

#13 Postby gatorcane » Wed Sep 20, 2017 7:58 pm

I agree we need a cone that represents the uncertainty at the time the advisory is made. If the models are in good agreement 5 days out, the cone should be smaller to reflect that. Conversely if the models diverge at 5 days out, the cone should be wider accordingly.

But I agree too many people focus on the line and whether they are in the cone or not. Irma is a good example. SE Florida moved out of the cone with line going through the west coast of Florida. A lot of folks in SE Florida were surprised how strong the winds got.
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Re: What the Cone Means

#14 Postby tolakram » Tue Oct 03, 2017 2:22 pm

http://www.nhc.noaa.gov/aboutcone.shtml

The cone represents the probable track of the center of a tropical cyclone, and is formed by enclosing the area swept out by a set of circles (not shown) along the forecast track (at 12, 24, 36 hours, etc). The size of each circle is set so that two-thirds of historical official forecast errors over a 5-year sample fall within the circle. The circle radii defining the cones in 2017 for the Atlantic and eastern North Pacific basins are given in the table below.
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