sHNVN20L44- Brian McNoldy September 30, 2022 It was ALWAYS in the likely (67%) area for landfall. In the four days before its landfall, Ian was close to the right-hand edge of each forecast cone.įor the sake of completeness, here is EVERY cone from Advisory 1 at 5am Friday morning to Advisory 24 at 11am Wednesday morning. But because of the two-thirds guideline, plenty of storm centers still can be expected to go outside the cone. (In theory, the cone could be enlarged to encompass a higher fraction of storms, but that approach would also increase the area covered by the cone and could be seen as over-warning.)Īs forecasts have improved over the years, the cone has gradually narrowed.
The radius of the circle at each time step is fixed such that two-thirds of all NHC track errors over the previous five years at that forecast time step (such as 48 or 72 hours) fall within the circle. The lines on each side of the cone are drawn to encompass eight circles (not shown in the graphic), with each circle corresponding to one of the time steps on the forecast track. One of the points that most often confuses the general public is that tropical cyclones often stray beyond the cone – about one-third of the time, in fact, as noted on the NHC’s explanatory page. I’ve never been a get-rid-of-the-cone kind of guy, but listening to the back and forth over whether Lee County was or wasn’t always in it might just convince me its time has passed.- James Franklin October 4, 2022 James Franklin, an NHC retiree who headed the center’s Hurricane Specialist Unit from 2009 to 2017, shared his mixed feelings about the cone in a Twitter thread that touched on many of the relevant issues. As Ian drew closer, the cone tightened and the Fort Myers area ended up on the right edge of the cone. The graphic shows the five-day forecast track (central black line), the uncertainty range (the cone’s edges), and the predicted strength on the Saffir-Simpson wind scale (the dots along the line, including the “M” denoting a major hurricane between Tampa and Fort Myers at almost the precise time Ian made landfall). EDT Friday, September 23, showing an impressive forecast nearly five days ahead of Ian’s landfall in Florida, before Ian was even a named storm. The “classic” cone graphic for Hurricane Ian issued at 5 p.m. (NHC provides versions of the cone both with and without the central line.) Figure 1. Many depictions of the cone, for example, still show the skinny line at the center, even though experts have long exhorted people to focus on the cone’s breadth rather than on the central line. The cone has spawned its own confusions, some of which came into sharp relief during Hurricane Ian. Yet many folks currently still misinterpret those numbers – believing, for example, that a “20% chance of rain” means it will rain 20 percent of the time, or that it “shouldn’t” rain at all, instead of that the chances of receiving at least 0.01 inch of precipitation at a given spot are two out of ten. For almost 60 years now, the National Weather Service (NWS) has issued probabilities of precipitation. But probabilities are a tricky thing to convey.
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