Hurricane Irma’s ‘Cone of Uncertainty’ Shifts: What Does it Mean?

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Hurricane Irma Cone of UncertaintyNational Hurricane Center

The “cone of uncertainty” refers to the hurricane graphic used by the National Oceanic and Atmospheric Administration (NOAA) and the National Hurricane Center (NHC), as well as other weather outlets, to determine a hurricane’s possible path. Since these massive storms are often challenging to predict, the cone is used to highlight a wide area where the center of the storm might go over a 5 day period.

  • It’s important to note that the “cone” does not take the size of any given storm into account. If you live outside of the “cone,” it is still possible that your area will be impacted.

You can read a description of how the cone is determined below.

“The ‘cone’ that you see on the NHC graphical forecast represents the probable track of a tropical cyclone’s center and is formed by enclosing the area swept out by a set of circles (not seen on the graphic) along with the forecast track at 12-hour intervals. The size of each circle is set at two-thirds of the historical forecast error over the previous five-year period. Based on those previous forecast errors, the entire track of the tropical cyclone can be expected to remain within the cone about 60 to 70 percent of the time. The cone becomes wider over time as the forecast uncertainty increases.”

If you have watched a weather forecast during hurricane season, you’ve probably seen a white “cone” on the National Hurricane Center’s graphic (pictured above). Different weather outlets may use different colors to represent their cone. For example, The Weather Channel uses a red cone.

When it comes to Hurricane Irma, the “cone of uncertainty” has changed a bit in the overnight hours. The photo below shows what the cone looked like on Monday and most of Tuesday.

Cone of uncertainty

National Hurricane Center

The following photo shows the current cone, which moves more east. This shift came a short while after the latest GFS model, which showed Irma taking a northern turn before hitting Florida’s west coast. The latest GFS model favors an eastern hug and has Irma hitting southern Florida before heading up the east coast.

Irma cone of uncertainty

The “cone of uncertainty” will be updated as soon as the NOAA can confirm another shift.