Accuracy of hurricane 'cone of uncertainty' and why it's hard to predict storm's path

The "cone of uncertainty" is the projected path and intensity of a hurricane or tropical storm issued by the National Hurricane Center. But it’s more complicated than you might think. 

The area of the cone represents the most likely track of the center of the storm. What you don’t see is that it’s actually comprised of circles with radii that encompass two-thirds of the NHC’s official forecast errors over the most recent five-year period, plotted along the forecast track every 12 hours out to 72 hours (three days), then in 24-hour intervals out to 120 hours (five days).

FOX 35 Storm Team Meteorologist spoke with FOX Weather Hurricane Specialist Bryan S. Norcross about the concept behind the National Hurricane Center's "cone of uncertainty," and why Tampa residents were initially told to prepare for a possible landfall near them. In fact, Hurricane Ian's cone, at different times, extended from Apalachicola all the way to Fort Myers.

What is the purpose of the hurricane cone of uncertainty?

"Well Brooks, I actually created the cone first in the 90s and the original thinking behind it was that we were using these dots as kind of the center line… and I thought, ‘well, that’s not a good idea," because there's all this intrinsic uncertainty in the forecasting system.  So I thought we need to look at this more broadly and that's where the cone came from.  The problem is that it gets talked about wrong, and I think most people don't understand it.  Only two-thirds of the time, the center stays within the cone… the bad weather always extends outside the cone."

According to the National Hurricane Center, the entire track of the center of a tropical depression, tropical storm, or hurricane is expected to remain within the cone of uncertainty 60 to 70% of the time, based on its forecast path accuracy over the last five years.

Forecast error has generally decreased over the past decade as the computer hurricane forecast models used by meteorologists become more advanced. 

The National Hurricane Center issues an updated cone of uncertainty every six hours for all active tropical cyclones in the Atlantic Basin – which includes the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. 

It should be noted that the cone of uncertainty only provides information about the forecast track and intensity of a tropical depression, tropical storm, or hurricane. It does not represent where any impacts such as strong tropical storm winds, storm surges, and heavy rain will occur. Many impacts from a tropical cyclone actually occur outside the cone because it does not factor in the size of a storm.

Additionally, the center of the cone of uncertainty isn’t necessarily the exact path a tropical cyclone will follow. Its center of circulation could track along the left side of the cone, the right side, or anywhere in between. contributed to this report.