The ‘cone of uncertainty’ can be confusing. Here’s how to read it.

A breakdown to understanding the National Hurricane Center’s Tropical Cyclone Track Forecast Cone.
The so-called 'cone of uncertainty' for Tropical Storm Nicole as of Tuesday afternoon.
The so-called 'cone of uncertainty' for Tropical Storm Nicole as of Tuesday afternoon. [ National Hurricane Center ]
Published Nov. 8, 2022|Updated Nov. 8, 2022

After a storm gets a name, it also gets a track.

Over the years, the official hurricane track from the National Hurricane Center has earned the nickname the “cone of uncertainty.” It’s full of colors, blobs and a cluster of graphics that can be confusing if weather isn’t your day job.

So where to begin? Here’s a guide to understanding the Hurricane Center’s official forecast track.

What is the ‘cone?’

The National Hurricane Center officially calls its track the Tropical Cyclone Track Forecast Cone. It was created in 2002, according to Brian McNoldy, a senior research associate at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science. The track is meant to communicate where the Hurricane Center believes a storm’s most likely path will be.

“It has always been constructed by using the National Hurricane Center’s own track forecast errors over the previous five years,” McNoldy said.

The cone is formed by connecting a set of circles (not pictured in the cone) along the forecast track and is intended to give an idea of the historical likelihood that the storm’s center will stay inside the cone. The cone is formed based on a two-thirds chance that the storm’s center will be inside the cone. That also means there is a one-third chance it will fall outside the cone.

Breaking down the forecast cone

The National Hurricane Center's track shows Tropical Storm Nicole reaching the east coast of Florida late Wednesday into early Thursday possibly at or near hurricane strength.
The National Hurricane Center's track shows Tropical Storm Nicole reaching the east coast of Florida late Wednesday into early Thursday possibly at or near hurricane strength. [ The National Hurricane Center ]

First off, everything you need to understand about the Hurricane Center’s track forecast is in a legend at the bottom of the graphic — from understanding the storm’s intensity to possible watches or warnings.

Let’s start off with the the little black “x” you see at the base of the cone — that’s where the storm is in real-time. Then, you’ll see a large blob surrounding the “x,” that’s the size of the storm, or how far the winds of the storm reach.

Take Tropical Storm Nicole, for example. It’s a massive storm, with winds that extend outward nearly 400 miles. The orange blob surrounding the “x” represents tropical storm winds. If the blob were to be red, then it would represent hurricane-force winds.

The white cone you see, what we often refer to the cone of uncertainty, shows where the storm could go in the next one to three days.

There are some misconceptions that the white cone accounts for the actual size of the storm, but that’s not true. What the cone actually represents is the forecast’s growing uncertainty as the forecast moves days away. The further out the forecast goes, the bigger the white area of uncertainty will be.

The dotted area that extends from the cone is the same — it’s the storm’s potential track four to five days from the forecast.

A look at watches and warnings

Watches and warnings are highlighted on the map of the official Hurricane Center’s forecast track. In the instance of Tropical Storm Nicole, nearly the entire coast line of Florida is under some kind of watch or warning.

The Tampa Bay area, for example, is highlighted in yellow, meaning the area is under a tropical storm watch.

A hurricane watch will be highlighted pink, a hurricane warning will be red and a tropical storm warning will be blue.

Also on the track legend are three letters “S,” “H,” and “M.” These letters account for the strength of the storm based on wind speed. An “S” has sustained winds of 39-73 mph (a tropical storm), an “H” has wind speeds of 74 mph to 110 mph (a category 1 or 2 hurricane) and an “M” stands for a major hurricane with wind speeds over 110 mph (a category 3 hurricane or above).

The Hurricane Center also attaches time stamps to the letters to let the reader know when and where these conditions are expected.

In the case of Tropical Storm Nicole, the hurricane center’s forecast has the Tampa Bay area within the cone around Thursday afternoon when forecasters anticipate Nicole to be at tropical storm strength.

Other graphics to look for

Over the years, the National Hurricane Center has created a number of graphics to account for the many hazards that a hurricane or tropical storm can pose.

The Hurricane Center’s track is already jam-packed with advisories and predictions, which has led to the agency creating separate graphics to account for things like storm surge, wind speeds and possible areas of flash flooding.

Some of the most dangerous aspects of a storm, and what often leads to evacuations, is the possibility of storm surge or flooding.

For a full list of these graphics, go to the National Hurricane Center’s website, click on the storm you’d like to learn more about and click on the graphics page, where you’ll find a treasure trove of information vital to understanding your own personal risk.

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