New Hurricane Cone Of Uncertainty Coming Soon

Impacts From Storms Go Well Beyond The Cone

The National Hurricane Center has announced that they’re redeveloping the famous cone of uncertainty to incorporate more forms of error.

The current cone of uncertainty: The forecast cone is formed by enclosing the area swept out by a set of circles 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 new cone of uncertainty: The circles that make up the current cone will become elliptical, or elongated circles, based on two different ways that we track errors.

Instead of the one radius that encapsulated most of the overall track error in the last five years, two different types of error will make up the shape of the cone:

• Forward speed or along-track errors: The distance that the center of a tropical system was behind or ahead of forecast

• Directional or cross-track errors: How far a tropical system deviates to the left or right of a forecast.

This means that the circles that previously made up the cone will now be ellipses.

The center of tropical systems will be expected to remain inside the ellipses 90% of the time.

The cone will continue to become wider as the forecast uncertainty increases with time, carving out the cone shape.

Most importantly, the cone of uncertainty still does not contain any information about the storm’s impacts, including storm surge, rainfall flooding or wind speeds. The cone only indicates the forecast track of the center of a storm. Other forecast graphics will show this information.

When to expect this change: The National Hurricane Center will display both versions of the cone side by side through this hurricane season. Should the new version of the cone be well-received, it could be made the official cone in the 2027 Atlantic Hurricane Season.

More information on the cone of uncertainty: Up until this proposed change, the current cone of uncertainty has been used since 2007 with annual changes to its width based on historical errors.

The width of the cone of uncertainty has gradually shrunk since then has forecasts have improved.

Jonathan Belles has been a digital meteorologist for weather.com for 9 years. His favorite weather is tropical weather, but also enjoys covering high-impact weather and news stories and winter storms. He's a two-time graduate of Florida State University and a proud graduate of St. Petersburg College.