The forecast cone explained- a moment of science

Storm Team 2

This graphic should be very familiar to everyone by now. Every hurricane season, every 3-6 hours, every storm- you see a different forecast cone on social media, from us, but do you know exactly what it entails?

There is a long winded definition given by the National Hurricane Center but the bottom line is that the cone is an easy graphical way to communicate uncertainty in forecasting hurricanes.

That uncertainty is due to various weather model’s interpretations to where the storm will go. It is rare for a single run of a computer model to get the track just right, but by laying out many we can establish a probable track. That track is rarely exactly right as well. That’s where this cone comes in.

The size of the cone comes from the historical error in hurricane forecasts over the past 5 years. Forecasts generally become more muddled and inaccurate the further one goes out- the reason why the cone expands. The cone has gotten smaller in recent years as our forecasts have gotten better- but they’re still not perfect.

The cone  represents the probable track of the CENTER of the storm. The center of the storm will stay within the cone ⅔ times, but does stray away from it 1 out of three times. This is why we emphasize that you should not just focus on the track line as it will move, especially 5 days out. The main use is to show you where the center may go, but many use the cone incorrectly.

Robbie Berg, Hurricane Specialist with the NHC, on what you shouldn’t take away from the graphic,

“Hazards associated with the storm usually extend out of the area of the cone. So don’t use the cone to assess the risk of storm surge, strong winds, heavy rain, or tornadoes. And since we prepare for a storm based on these hazards- don’t use the cone to determine if you should evacuate or prepare.”

This cone just tells one part of the story, to fully understand your risk and establish your hurricane plans you should seek out trusted sources to incorporate other graphics that illustrate impacts.

Hopefully by better understanding this, at times, confusing graphic you can better understand our forecasts and better assess your risk.

Storm Team 2 Meteorologist David Dickson

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