The cone is the most recognized graphic in hurricane forecasting and the most misread. It is built from past forecast performance, not from anything about the storm being shown.
What the cone is drawn from
Forecasters plot a center track showing where the storm center is expected at successive future times.
A circle is then drawn around each of those points, sized so that the storm center has historically fallen inside it in a large majority of past cases at that lead time.
The cone is simply the swept outline of those circles, and its width comes entirely from the accuracy of recent forecasts rather than from the current situation.
Why it says nothing about size
The cone describes the possible positions of a single point, the center of circulation, and a hurricane extends far beyond that point.
Tropical storm force winds routinely reach outward well past the cone boundary, and rainfall and surge extend further still.
A location outside the cone is therefore not outside the storm, which is the misunderstanding responsible for the most consequential unpreparedness.
Why the cone has narrowed over time
Because the width is derived from historical error, improvements in track forecasting shrink it automatically as older, less accurate years leave the sample.
Track accuracy has improved markedly through better satellite coverage, more capable models and better use of aircraft observations.
The narrowing is genuine progress, but it also concentrates attention on a smaller area and can strengthen the false impression that the cone bounds the danger.
What the cone leaves out entirely
Storm surge depends on coastline shape, water depth offshore and the angle of approach, so the surge threat is mapped separately and does not align with the track.
Inland flooding depends on rainfall and river basins, and often affects areas far from the coast after the center has passed.
Tornadoes in the outer bands occur mainly on one side of the storm, in a region that the cone does not describe.
How to read it correctly
Treat the cone as a statement about uncertainty in position, and treat the separate wind, surge and rainfall products as the statements about hazard.
The center passes outside the cone in a meaningful minority of cases, which is a designed property rather than a failure.
Decisions should follow the local watches, warnings and evacuation orders, which incorporate all of the hazard information rather than the track alone.