One More Comment on the Cone

When I was the Director of the National Hurricane Center (NHC) I was often asked why a certain location remained under tropical storm or hurricane watches or warnings when the so-called “Cone of Uncertainty” was not even over that location.

Let’s take a simple example.  The graphic below shows the track forecast cone of Hurricane Ike from 2008 from 2:00 pm Tuesday 9 September 2008.  The center of Ike is located over western Cuba and the cone is pointed into the Gulf of Mexico toward Texas.

Ike cone from 2 pm EDT Tue 9 September 2008

Ike cone from 2 pm EDT Tue 9 September 2008

At the time of this forecast, the cone did not cover the Florida Keys.  Yet a tropical storm warning remained in effect for the Florida Keys.  This is because the radius of tropical storm force winds extended out approximately 150 nautical miles (175 statute miles) to the northeast of the center of Ike.  In fact, the lower Keys were getting sustained tropical storm force winds at this time (45 knots sustained with gusts to 52 knots).

It is important to remember that the cone represents the probable track of the center of a tropical cyclone.  The cone is constructed such that two-thirds of the time, the track of the tropical cyclone stays within the cone.  The cone does not say anything about the distribution of the winds, storm surge, rainfall or tornadoes.  Other products address those hazards.

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