The cone of uncertainty; there are important changes this year

DURHAM, N.C. (WTVD) -- Hurricane season runs from June 1 through Nov. 30, and there are two main areas where these storms typically form. Out in the Atlantic Ocean, storms often begin as wind coming off the west coast of Africa, near places such as Senegal, the western Sahara, and Mali, picking up energy from the warm waters of the Atlantic.

These winds can develop into areas of low pressure, and with enough warm ocean water and low wind shear, they can grow into tropical storms and eventually hurricanes moving west across the Atlantic. As we get deeper into the season, this becomes the primary hotspot for hurricane development.

But earlier in the season, development is often much closer to home -- in the Gulf of America and along the Southeast coast. Here, storms often form along stalled fronts. When those systems interact with very warm water, they can quickly take on tropical characteristics and strengthen. Once a storm develops, the National Hurricane Center issues its official forecast.

And that brings us to something you've probably seen many times -- the cone of uncertainty. You've seen it. You're familiar with it. But this year, there are some important changes.

The cone is based on past forecast errors in the past five years. It's created by plotting a series of points along the storm's predicted path at 12, 24, 36, 48, 72, 96, and 120 hours.



Around each of those points, a circle is drawn based on five-year historical errors. Until now, that cone has represented about a 67% confidence range, meaning the storm's center stays inside it roughly two out of three times.

This year, there's something new -- an experimental cone. Instead of circles, it uses ellipses and expands to roughly a 90% confidence range. In other words, the storm is now expected to stay inside the cone about 9 out of 10 times, giving you a clearer picture of just how uncertain the forecast can be.

There are a few more updates you'll notice this season:

Inland alerts will now appear directly on the cone -- not just along the coast.

The shading has been simplified. A single color will now represent the full five-day forecast.



And there's a new symbol, showing areas where a hurricane watch and tropical storm warning are both in effect at the same time.

So as you track storms this season, these changes are designed to give you a clearer, more realistic view of the forecast.

And as always, count on the First Alert Forecast Team to stay informed and stay safe.

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