The National Hurricane Center’s forecast cone graphic gives a quick read on where a tropical cyclone is headed and how much uncertainty surrounds that track. Knowing the colors, the dots, and the shaded areas turns the cone into a planning tool, not just a map.
What the colors and dots mean
The graphic layers watches and warnings around the storm’s current and forecast positions. The orange circle marks the present location of the center. The dots along the path show where the center is forecast to be at later times.
A black dot means the system is forecast to stay tropical. A white dot with a black outline means it is expected to be extratropical. A lone "L" means the system is forecast to weaken to a remnant low.
The letter inside each dot gives the forecast intensity:
- D: tropical depression, winds below 39 mph
- S: tropical storm, winds 39 to 73 mph
- H: hurricane, winds 74 to 110 mph
- M: major hurricane, winds above 110 mph
The shaded areas in the background show where hazards are in effect. Red marks a hurricane warning, pink a hurricane watch, blue a tropical storm warning, and yellow a tropical storm watch. The orange fill on the cone itself represents the forecast uncertainty, not the size of the storm.
How the cone is built
The cone is a measure of track forecast error over the past five years. The Hurricane Center places imaginary circles along the official forecast track at 12, 24, 36, 48, 72, 96, and 120 hours out. Each circle is sized so that it encloses 67 percent of the previous five years of official forecast errors at that lead time. The cone is then drawn by connecting the swept area of those circles.
The solid white portion covers days 1 through 3 of the forecast. The stippled white portion extends that range to days 4 and 5. Historical data indicate the entire five-day path of the cyclone’s center stays inside the cone roughly 60 to 70 percent of the time.
Why the storm is bigger than the cone
A tropical cyclone is not a point. Hurricane force winds, one-minute averages of at least 74 mph, and tropical storm force winds, 39 to 73 mph, can reach hundreds of miles from the center. The cone only traces where the center is most likely to go, so damaging winds, heavy rain, and storm surge often sit well outside the white area.
For a true read on how far the wind field extends, the Hurricane Center points to its separate Wind History graphic. To check the odds that a specific location will feel tropical storm force, 50 knot, or hurricane force winds, the Wind Speed Probabilities product provides those numbers in tabular and graphical form for the 34 kt, 50 kt, and 64 kt thresholds.
Where the cone fits in the forecast suite
The cone graphic is one piece of a larger package. The Hurricane Center publishes public advisories, forecast advisories, forecast discussions, and wind probability tables alongside it. Related products also cover storm surge inundation, peak surge, rainfall potential, flash flooding potential, and tornado potential. A set of static and interactive cone maps, including an experimental version, offers longer or shorter views.
Common reading mistakes to avoid
Two errors come up often when people use the cone. First, the cone is not a risk area. Storms are not expected to fill it, and danger does not stop at the edge of the white shape. Second, the cone ignores intensity. A compact hurricane and a sprawling tropical storm can sit inside the same oval, so the Wind History and Wind Speed Probabilities products matter as much as the cone itself when planning.
FAQ
What does the cone of uncertainty represent?
It is a smoothed shape built from five years of official forecast errors. The solid white area covers days 1 through 3 and the stippled white area covers days 4 and 5, so the entire five-day center track stays inside the cone about 60 to 70 percent of the time.
How is the size of the cone determined?
Imaginary circles are placed along the forecast track at 12, 24, 36, 48, 72, 96, and 120 hours. Each circle is sized to enclose 67 percent of the previous five years of forecast errors at that lead time, and the cone connects the swept area.
Does the cone show where damaging winds will occur?
No. The cone shows only the likely path of the storm’s center. Hurricane and tropical storm force winds can extend hundreds of miles from the center, so the Wind History and Wind Speed Probability products are needed to see how far the hazards reach.
This article summarizes reporting from nhc.noaa.gov.