Q&A – National Hurricane Center’s Cone Accuracy

Today’s entry: I’ve noticed the Hurricane Center’s cone is narrower than it used to be but it seems like the projected path changes just as much as it ever did. Is there any info you have on how much it still changes?

Bottom Line: I can hear the National Hurricane Center’s Dennis Feltgen in my head right now. Don’t focus on the center point of the projected path. Pay attention to the cone. We’re naturally drawn to the center point of projected paths for tropical events. Hurricane Isaias has been no different. Within a matter of 24 hours Wednesday into Thursday the center point of the path suggested the storm might make a direct landfall in Southeast Florida, a landfall on Florida’s gulf coast and back to skirting southeastern Florida. If you follow the center of the path it feels like the forecasting is moving around all over the place. In reality, if you look at the original cone, and simply track how it’s narrowed as the storm moves closer, you’ll notice not much has changed since the original wide cone encompassing South Florida.

It’s far from an exact science as the National Hurricane Center meteorologists are quick to point out, but it is an improving science. In recent years it’s not just that the cone of uncertainty has become smaller, it’s that forecasting has generally become more accurate. Clearly, the longer the range of the forecast the greater the uncertainty. But what difference does a day make in forecasting these days? About 40 miles.

Naturally, the five-day forecast introduces the greatest uncertainty but even then, it’s pretty good these days. By the numbers, 67% of the time the system travels through the cone of uncertainty and the margin of error is 210 miles.

Now, what do those 210 miles represent? Five days out the average storm passes 210 miles from the center of the projected path. It’s 350 miles from Miami to Jacksonville. And only about 110 miles from the east coast of Florida to the west coast in South Florida.

The NHC’s accuracy improves about 40 miles per day. 

  • Four days out: 170 miles of variance
  • Three days out 130 miles of variance
  • Two days out 90 miles of variance
  • One day out 50 miles of variance

For perspective on the 50 miles, that’s about the distance from Miami to Boca. That’s pretty good in perspective. And that’s the current accuracy of the National Hurricane Center’s projections.

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Photo by: ERIKA SANTELICES/afp/AFP via Getty Images

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