What Does a Hurricane Forecast Cone Actually Show?
The cone shows the probable track of a tropical cyclone’s center; it does not show the storm’s full size or every location at risk from wind, rain, surge or tornadoes.
Timeline
- Forecast issuance: NHC plots the forecast center positions and builds the cone around historical track-error statistics.
- During the forecast: The storm center can travel outside the cone and hazards can extend far beyond it.
- Local decision-making: People should use watches, warnings and local hazard products in addition to the cone.
A National Hurricane Center forecast cone represents the probable track of a tropical cyclone’s center. It does not outline the physical edge of the storm. Rain bands, tropical-storm-force winds, storm surge and tornadoes can occur well outside the cone, while some locations inside it may avoid the worst conditions. [1][2]
The cone is constructed around the forecast positions of the storm center using historical forecast errors. NHC sets its size from error statistics and updates those values as forecast skill changes. The center is expected to remain within the cone for much, but not all, of the forecast period. [2]
A narrowing cone toward the present does not mean the storm itself is shrinking. It reflects lower track uncertainty at shorter lead times. Likewise, a widening cone farther into the future reflects increasing uncertainty about the center’s path, not a prediction that the cyclone will grow wider. [2]
Track and intensity are different forecasts. Two paths inside the cone can produce very different wind and surge outcomes, and a small track shift near land can move the highest surge into another bay. The cone should therefore be read with intensity forecasts, wind-probability maps, rainfall outlooks and storm-surge products. [1][2]
Milton in 2024 illustrated the distinction: the official archive includes separate advisories, discussions, wind products and surge information because no single graphic captures all hazards. Local watches and warnings communicate the conditions expected in a specific area and are more relevant to immediate protective action. [1]
People should not wait for their location to appear on the center line. The line is only one forecast path and receives no special guarantee. Emergency instructions from local authorities, evacuation zones and flood risk should control decisions rather than the visual boundary of the cone. [1][2]
Forecast graphics also change from one advisory to the next as observations and models are updated. A shift does not necessarily mean the earlier forecast was careless; it reflects new evidence and the uncertainty inherent in predicting a moving atmosphere. Save the advisory time when sharing a map, because an old cone can become dangerously misleading after a newer forecast is issued. [1][2]
Sources
- National Hurricane Center — Hurricane Milton advisory archive
- National Hurricane Center — Definition and use of the forecast cone