One of the most misunderstood and misused products created by the National Hurricane Center is the probability cone, or cone of uncertainty or, as I call it, the cone of shame. I personally deeply dislike this product, not so much because it is a bad product, but because it is so misunderstood and misused.
Despite the very clear label at the top, TV “news” people and the weatherblogging community take this graphic and data and repackage it in to stuff like this:
It’s misleading for a lot of reasons. The cone is showing the area within which there is a 2 in 3 chance (67%) the center of the storm will fall based on the average NHC forecast errors over the last few years. That’s useful information, but there are two missing components, as the NHC graphic shows but is often left out when repackaged.
First, storms aren’t points. They usually often aren’t even disks, one side (typically the right) will be stronger than the left. Significant impacts can extend well outside the cone. Here is the 5am forecast cone for TD9/FutureImelda, along with the TAOS(tm) TC model wind swath.
Notice that none of Florida is within the cone of shame – yet will likely see some storm impacts. And that is if the forecast is perfect – wobble the storm left a little, or if it’s a little stronger, it’s much worse.
The second issue is the cone doesn’t take in to account the forecast uncertainty for any individual storm. Some storms are easier to forecast than others. Although we only have about two days of forecasts, here is a display of forecast uncertainty based on the performance on TD9 and the error trends so far for both the official and global models. These are complex outputs, but the easy version is that this is a very complex situation and the error potential is a lot greater than the cone shows, and not really centered on the track, especially for a system interaction with another strong hurricane as well as surrounding weather like the front off to the west..
And, this is just for location – throw in intensity, and you can see that the cone can be misleading – especially if you strip off the NHC cautions! This is why I don’t use it, but talk about uncertainty, wobbles, and alternate scenarios.
So be careful when using the cone. It is an indication of where the storm center might be relative to the track line, but that’s not telling you much about potential impacts at your location.
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