Thu Sep 07 2017 04:28 AM

Lounge Reminder ...

It's foolish to consider the spaghetti and make decisions - any decisions - Even if one knows.. like really, really knows, what they are looking at. Forecast errors beyond 48/72 hours can be large. When in the Lounge, extreme caution is always advised.

About the spaghetti.. There is no *one* model that forecasters consider solid gold. Some handle certain situations better than most. And then some that perform poorly in one scenario, outshine in yet other situations. This is why human forecasters rely (still, for now) on some good ol' human brain power, along with weighted averaging super consensus models (models based on models, weighted for accuracy and relevance).

Within models, there are individual members ('ensembles'), and also the 'operational' version of that model. The operational is not the same as the model mean, incidentally. There is also that, and it's called, aptly, the "Mean."

The operational is the standard within that model family, but not necessarily always and every time the best version of that model. So, forecasters also consider the entire sphere of a model's ensembles, and, because this is the Lounge, and we are talking spaghetti, I'm sharing some of the top global models' ensemble runs from 07 0z. to give some idea of how much uncertainty there remains after 72 hours. There really is a lot. Therefore, use this intel to help you not decide whether or not model x or model y gives you warm n fuzzies about not having to worry, but rather an illustration as to why, beyond 72, heck, even 48 hours, one should pay way, way, way less attention to the 'center line,' and far more to the outermost bounds of the NHC Cone of Uncertainty.

What is the Cone of Uncertainty? It is that apparition that surrounds the 'center line' that people often misinterpret to be a region of any impacts, when in reality, it designates the range in which .. get this .. if you don't already know... maybe you'll want to even sit down first ... the Cone of Uncertainty actually '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.'

Did you catch that? In other words, its highly likely that the actual track is not going to be going right down the center line, but rather to the right or left of it (and possibly well to the right or left in some storms - possibly how far left or right? Look at the current NHC Cone).

On to some images of the most recent 07 0z Ensembles on Irma. Again, please use with extreme caution. This is not a forecast. This is a series of model outputs that describe a range of possibilities identified by a parent model.

Note: This is NOT an official page. It is run by weather hobbyists and should not be used as a replacement for official sources. 
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