How to Read the Forecast Cone
The forecast cone, officially the Track Forecast Cone, is the National Hurricane Center's best-known graphic. It shows the predicted path of a storm's center over five days. But it is also the most misunderstood product the NHC publishes, and misunderstanding it has gotten people killed.
The cone is a historical accuracy envelope, not a danger zone. Its width is based on the NHC's track error over the past five years. Two-thirds of the time, the storm center stays inside the cone. That means one-third of the time it does not. The cone says nothing about the size of the storm, the wind field, the rain, or the surge.
What the cone tells you
- The most likely path of the storm center over the next 5 days.
- The uncertainty in that track, which grows with time. The cone widens at day 5 because forecast error grows.
- The current watch and warning areas along the coast, shown in color.
What the cone does not tell you
- The size of the storm. Hurricane-force winds can extend 50 to 100 miles from the center, so impacts occur well outside the cone.
- Storm surge. Surge is driven by the storm's size, angle, and the shape of the coast, not just the track. The NHC issues a separate storm surge watch and warning graphic.
- Rainfall and flooding. A storm can cause catastrophic flooding hundreds of miles from the cone, as Florence did in North Carolina in 2018.
- Tornado risk. Tornadoes often occur in the outer bands far from the center.
The mistake people make
The most common and dangerous mistake is checking whether the cone crosses your town and deciding you are safe if it does not. Ian in 2022 was forecast to hit Tampa two days before landfall. The cone shifted south, and Lee County residents who had not prepared were caught by a 10-to-15-foot surge. If you are within 100 miles of the cone at any forecast hour, prepare as if the storm is coming to you, because the track can shift and the impacts extend beyond the line.