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Definition of the NHC Track Forecast Cone


Definition:

The cone represents the probable track of the center of a tropical cyclone, and is formed by enclosing the area swept out by a set of circles (not shown) along the forecast track (at 12, 24, 36 hours, etc). The size of each circle is set so that two-thirds of historical official forecast errors over a 5-year sample fall within the circle. The circle radii defining the cones in 2017 for the Atlantic and eastern North Pacific basins are given in the table below.

One can also examine historical tracks to determine how often the entire 5-day path of a cyclone remains completely within the area of the cone. This is a different perspective that ignores most timing errors. For example, a storm moving very slowly but in the expected direction would still be within the area of the cone, even though the track forecast error could be very large. Based on forecasts over the previous 5 years, the entire track of the tropical cyclone can be expected to remain within the cone roughly 60-70% of the time.

Radii of NHC forecast cone circles for 2017, based on error statistics from 2012-2016:

Forecast Period
(hours)

2/3 Probability Circle,
Atlantic Basin
(nautical miles)

2/3 Probability Circle,
Eastern North Pacific Basin
(nautical miles)

12 29 25
24 45 40
36 63 51
48 78 66
72 107 93
96 159 116
120 211 151

Example Graphic of 5-Day Track Forecast Cone:

Tropical Cyclone Track and Watches/Warnings
image example for Hurricane Sandy