ATL: CRISTOBAL - Post-Tropical - Discussion

[fci]

wfor weather making look like south fl we in clear

Clear to me is when a system has passed.
Even then I casually follow until I know it's gone.
I'm old enough to remember Betsy and most of us experienced Jeanne that was progged to be a "fish".
I wouldn't give an "all clear" either as long as the NHC says there is uncertainty in the future track. Looks good for South Florida and that's what they should be saying.

[artist]

That just doesn't sound right to me. Could you please explain?

My understanding is it does include model guidance, but also includes historical data.
IF it didn't take models into account, then we wouldn't need models. Just my understanding.

The cone is SOLELY based upon the 5 year mean error. No model guidance is included.

I believe there are private companies that do include forecast uncertainty in their cones, however

Thanks for the correction. I am wondering though, why do we have models, if not to give an idea of where a storm might track?
Realize i am not questioning your answer, it just raises questions for me as to why are models mentioned within a forecast, if they are not considered. Something I am sure many others would like to know as well.

[HurricaneBelle]

The models have an indirect relationship to the "cone" in that they're used by NHC to calculate the projected track. But once the track is calculated, the cone is based on the average error by future time period, as wxman et al have noted.

[Hurricane Andrew]

And away we go...

[jinftl]

Current NHC forecast has the probability of sustained tropical storm force winds (39 mph) in a 20-30% swath for the FL East Coast from Miami up to Daytona. This graphic is updated every 6 hours along with the forecast track and 'cone'.

Reminds us that storms have peripheral effects even if you are not in the path of the center/eye

[Hurricane Andrew]

Latest VDM over on recon has extrapolated surface pressure down to 1003mb from 1005mb. .

[Alyono]

Thanks for the correction. I am wondering though, why do we have models, if not to give an idea of where a storm might track?
Realize i am not questioning your answer, it just raises questions for me as to why are models mentioned within a forecast, if they are not considered. Something I am sure many others would like to know as well.

The models are used to make the forecast itself

[Nimbus]

Be interesting to see how the cone migrates over time.
Looks like the outflow is expanding as though under building high pressure.
The hot towers are being sheared east a bit at the moment.

[artist]

The models have an indirect relationship to the "cone" in that they're used by NHC to calculate the projected track. But once the track is calculated, the cone is based on the average error by future time period, as wxman et al have noted.

Thanks for the clarification. So they are considered in where the track is projected, but the 'cone of error' size is determinined by historical/climatological data. Thanks, Alyono. Did I get that correct?

[jlauderdal]

wfor weather making look like south fl we in clear

they arent going to deviate from nhc and start going into a bunch of scenarios..its hard enough to get the public to take action when there is something as basic as a hurricane warning...however, the media makes a ton of mistakes with terminology, info and facts..we could have an entire thread on that for each storm

[GCANE]

The ULL to the west continues to move away at a good pace.

Currently over the Florida straights.

http://tropic.ssec.wisc.edu/real-time/w ... oom=&time=

[artist]

Thanks for the correction. I am wondering though, why do we have models, if not to give an idea of where a storm might track?
Realize i am not questioning your answer, it just raises questions for me as to why are models mentioned within a forecast, if they are not considered. Something I am sure many others would like to know as well.

The models are used to make the forecast itself

I think that is where the disconnect came in. The cone is drawn around the projected path, thus the understanding to some of us it includes model guidance for where that cone will be drawn.

[Portastorm]

Hey gang, while I understand and appreciate the merits of the discussion here about the NHC cone and it's relationship (or lack thereof) with computer models has been enlightening and educational, any further discussion in a general sense about this topic should be moved to Talkin' Tropics with a new thread created.

Let's please focus on TD #4 in this thread and what's going on with the system. Thank you!

[Chris_in_Tampa]

Thanks for the correction. I am wondering though, why do we have models, if not to give an idea of where a storm might track?
Realize i am not questioning your answer, it just raises questions for me as to why are models mentioned within a forecast, if they are not considered. Something I am sure many others would like to know as well.

For indepth reading on how the cone is set each year:
http://www.nhc.noaa.gov/verification/verify4.shtml

The track line and points are set by the National Hurricane Center, based on using all the information available to them, including models. Then at each point along the track, which are at the hours in the first image at that above page, they use the error radius to draw a circle around each of those points.

The WunderMap is probably a great way to visualize the cone:

http://www.wunderground.com/wundermap/? ... t=0&favs=0

You can see the cone is actually made up of circles around each forecast point, the radius determined by the 5 year error by the NHC. Error radii are calculated for each individual basin.

Once you have the circles, a line is drawn around it all to make the cone.

2/3rds of the time on average over the past 5 years, 2009 to 2013, the center point of the storm (Updated: I had initially simply said storm) will be within those circles. The important thing to know, that even some professional mets really don't emphasize enough, is that 1/3 of the time on average over the past 5 years, the center point of the storm (Again updated, I had initially simply said storm) was NOT within that area. People should absolutely pay attention to the cone, but also realize that just because you are not in the cone does not make you safe.

So, looking at the WunderMap above, all the East Pacific storms have the same error cone circle size, at their respective hours. The Atlantic has their own specific error circle radii at each hour.

The cone error radii, for each basin, are set before the season starts each year.

The Weather Channel might be one of those who actually have their own cone. I don't know if they still do for sure, but in the past they definitely have. In the past they said something like, forecast wind speeds are from the National Hurricane Center and those speeds were overlaid on their own cone. (Their specialized version of the cone may have been based off the NHC track exactly, just drawn with connecting circles they came up with based on uncertainty, but it was unclear, which was the problem.)

Important Addition (and two important modifications above):

One thing I forgot to add is that a storm is not a point of course. Effects can be felt hundreds of miles away from the actual center. So even if the center point is in the cone, some people outside of the cone could still be significantly impacted. If the center road the edge of the cone, the worst impacts could potentially be outside the cone. If the storm is out of the cone of course, people very well outside an earlier cone could be impacted.

And see the two updates above where I changed it from "storm" to "center point of the storm".

[Nimbus]

The ULL to the west continues to move away at a good pace.

Currently over the Florida straights.

http://tropic.ssec.wisc.edu/real-time/w ... oom=&time=

There is an upper level low keeping pace with TD4's anticyclone as well.
Watch all 30 frames of this WV loop.

http://wwwghcc.msfc.nasa.gov/GOES/goeseasthurrwv.html

[cycloneye]

SUMMARY OF 800 PM AST...0000 UTC...INFORMATION
----------------------------------------------
LOCATION...22.0N 72.4W
ABOUT 80 MI...130 KM NE OF GREAT INAGUA ISLAND
ABOUT 245 MI...395 KM ESE OF THE CENTRAL BAHAMAS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 11 MPH...18 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES

[Hammy]

The ULL to the west continues to move away at a good pace.

Currently over the Florida straights.

http://tropic.ssec.wisc.edu/real-time/w ... oom=&time=

There is an upper level low keeping pace with TD4's anticyclone as well.
Watch all 30 frames of this WV loop.

http://wwwghcc.msfc.nasa.gov/GOES/goeseasthurrwv.html

I notice the upper air environment does indeed seem to be changing a bit over the system, or at least to the west, as if you pick a point on the map west of the depression, the upper flow becomes out of the east whereas it started out from the south.

[mitchell]

The error cone includes no model guidance at all. It is absolutely the same size for all storms and all advisories (this year). The cone represents the 66.7% error calculated in the years 2009-2013. Basically, based upon NHC errors over the past 5 years, the cone represents a 66.7% chance that the center will track within it.

THANK YOU! One of the most helpful posts i've seen. I've always wondered why the cone is so symmetrical, and keeps the same forward speed and intensity for both sides of the cone, even for a storm where one side of the cone is completely over land for a long time and other side of the cone is over warm water for a long time.

[Nimbus]

The ULL to the west continues to move away at a good pace.

Currently over the Florida straights.

http://tropic.ssec.wisc.edu/real-time/w ... oom=&time=

There is an upper level low keeping pace with TD4's anticyclone as well.
Watch all 30 frames of this WV loop.

http://wwwghcc.msfc.nasa.gov/GOES/goeseasthurrwv.html

I notice the upper air environment does indeed seem to be changing a bit over the system, or at least to the west, as if you pick a point on the map west of the depression, the upper flow becomes out of the east whereas it started out from the south.

The ULL over Belize has been slowly migrating west as well, making room for high pressure to fill in.

Last recon report I saw had the central pressure at 1003 Millibars and with the broad circulation hindering it could take 24 hours to reach 995 MB.

[KBBOCA]

This has to be the biggest I've seen the cone since TS Debby, still somewhat suprised that at least extreme coastal parts of Florida aren't in the cone.

They are in the cone but right on the very edge.

If I understand correctly, the large width of the cone is due to the projected slow movement.

Also, I hope people remember that the cone does not show expected area of impact, only the area where the center of the storm is projected track. Depending on the west side of the storm, even if this system stays off to the east of Florida, there could still be strong effects from the storm outside of the cone. That was the case in 2012 with Isaac. Areas of FL were under watches and warnings that were not in the cone and they were impacted by the storm.

http://en.wikipedia.org/wiki/Effects_of ... in_Florida