Tracking the Tropics: Explaining the ‘Cone of Uncertainty’

Weather Blog

AUSTIN (KXAN) — Hurricane Dorian continues to strengthen in the Atlantic with the forecast as of Friday at 11 a.m. showing the storm as a Category 4 (with sustained winds +130 mph) by landfall along the eastern coast of Florida. The exact location of Dorian’s landfall is still in question, but the cone of uncertainty includes the entire state. So what does that mean?

Hurricane Dorian forecast valid August 30th 11AM

Cone of Uncertainty explained

The “Cone of Uncertainty” indicates the probable track of the center of a tropical storm or hurricane. The size of the cone is the same for every storm in any given season and determined by statistics. Forecasters at the National Hurricane Center use the average track errors of tropical storms over the past 5 years to draw out the size of the cone. As the forecast extends out, the greater the chance for error and therefore, the wider the cone.

Over the last 15-20 years, the size of the cone has shrunken. This is due to the fact that we now have better technology to track and forecast hurricanes (computer models), more resources to observe them and a better understanding of hurricane processes. More accurate forecasts lead to smaller errors and therefore, smaller cones.

Shrinking cone of uncertainty over the last 15 years as forecasting technology and knowledge has improved.

Cone misconceptions

Cones are often misunderstood. Here a few reminders to keep in mind when looking at a hurricane’s cone:

  • The cone indicates the probable track of the storm’s center, not the whole storm. Just because your home may lie outside of the cone doesn’t mean you won’t see any impacts. The cone outlines where the center of the storm may go and is not an outline of its impacts.
  • The cone says nothing about the storm’s impacts or size. You will not be able to know how high the storm surge may go, how strong the winds will be or how much rain will fall just by looking at the cone.
  • The track may, in fact, shift outside the cone. Nothing is impossible.

A key thing to remember when a hurricane or tropical storm poses a threat to land is to stay up-to-date. The forecast is ever-changing when tracking these powerful storms. It is crucial that you stay aware of the changes that come with predicting hurricanes.

Key points: ‘Cone of Uncertainty’

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