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How the hurricane cone of uncertainty can be a cone of confusion, and what to do about it

Improved hurricane track forecasts have shrunk the cone. This is good, but it’s also bad.

The National Hurricane Center cone of uncertainty for Hurricane Dorian, issued at 2 p.m. Wednesday.

The ubiquitous hurricane forecast cone of uncertainty has shrunk again. This is the graphic that shows where the National Hurricane Center thinks the center of a storm, such as Dorian, could reasonably go.

Capital Weather Gang’s Brian McNoldy calculates that the middle of the cone is about 8 percent narrower this year than last. The width is based on the past five years of errors in National Hurricane Center forecasts, and the forecasts are getting better.

Clearly, better forecasts are good, but there’s also a downside. In almost every intense hurricane, dangerous weather is likely to occur outside the ever-narrower cone’s boundaries.

Less clarity in communication is an unintended consequence of more accurate forecasts.

Underlying this issue is the tug-of-war between definition-based and common-sense communications. The common-sense understanding of words and graphics will always trump the book definition. Most people never encounter extreme-weather terminology or graphics, except when something bad is in the works. The communications system has to work for experts and first-time users. The hurricane forecast cone is a poster-child for this reality.

The current cone is elegant in its simplicity and is phone-friendly, which is why it’s the main piece of hurricane-forecast information people search out on websites and apps. Heart rates elevate for people “in the cone” of a threatening hurricane, of course. But how are people outside the cone supposed to feel?

Over the years, the answer to this question has changed. The technical definition underpinning the size of the cone has steadily made the question, “Am I in the cone?” in essence, invalid.

Now, while the shrunken cone graphic technically matches the book definition, it is misleading to those who just want to know if they are in the threat zone.

The wider cone worked in the old days because significant hurricanes near the coast are almost always better forecast than weak storms that meander around in the middle of the ocean. The National Weather Service deploys all of its resources to make the best forecast for hurricane landfalls that science will allow.

That means that forecasts for a storm’s landfall generally have less error, usually by a lot — so hurricanes approaching land usually track near the center of the cone. When the cone was big, there was a decent chance the worst weather would occur inside the cone’s boundaries. The common-sense understanding of the cone as a threat or impacts zone generally worked.

The National Hurricane Center understands that the modern skinny cone can be a source of confusion, and a major effort is underway to come up with a new and better kind of cone. We all hope for speedy progress. But there are things we can do now.

With every advisory, the center produces data showing how far outside the cone dangerous winds might occur. Standardizing a graphic that combines the traditional cone with the wind-threat zone might help clarify the width of the storm. Weathercasters can do this now, but the resulting graphic is, in a word, ugly. Design improvements are needed if it’s going to work for prime time, and there needs to be an official National Hurricane Center version if the graphic is going to get traction.

Meanwhile, work can continue to design a new cone that is clear and concise — perhaps it expands and contracts depending on forecast certainty, among other refinements. Modern technology offers many possibilities that didn’t exist when we put the first cones on television in the 1990s.

Common sense says that the area inside the cone is the danger zone and outside the cone is safe or safer. We are not going to change that paradigm. But if the areas threatened by wind were delineated in a clear, consistent and media-friendly way, it might be possible to gradually change the public’s perception of the threat zone and how to determine if you’re in or out.

In the end, whatever new technical definitions and parameters are used to underpin the next generation of the cone graphic, one important question has to have a clear meaning again: Am I in the cone?

Bryan Norcross is a hurricane specialist at WPLG-TV in Miami and the Weather Channel.

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