Forecasters predicted a right turn would drive Hurricane Irma into an anxious Florida four days before the Cat 4 colossus did just that, biting into the side of Cudjoe Key.
With more than 1,100 miles of bathwater-warm Atlantic to cover before Irma was to reach the Peninsula’s tip, there was uncertainty that early morning of Sept. 6 whether the barreling circle of thunderstorms would rise up to buffet the east or west coast of the Sunshine State.
But the 90-degree turn anticipated 96 hours in advance is touted as a forecasting triumph.
This hurricane season, the successes of 2017’s forecasts will be reflected in a smaller cone of uncertainty — that ominous funnel of angst no one wants pointed at them.
While the tweak from this past season will likely go unnoticed by most, forecasting improvements since 2010 have resulted in an up to 36 percent smaller cone depending on the forecast period. Go back to the 1980s, and the reduction in forecast track error is closer to 80 percent, said National Hurricane Center deputy director Ed Rappaport, during March’s National Hurricane Conference.
“There have been many remarkable advances in science, but I would argue, given the complexity and importance to society, this improvement belongs on that list,” Rappaport said.
The hurricane center made 407 official forecasts during the hyperactive 2017 season. The cone graphic is by far the most viewed tool on the center’s website, with up to 60 percent of users looking to it for guidance.
With family on both of Florida’s coasts, Tequesta resident Kathy Foos is an avid cone-watcher.
“I’m always wondering who will be impacted,” she said. “Sometimes (family members) come to our side, or we go to theirs. Other times, there’s no good place to go.”
The cone as it’s known today was introduced in 2002, and has undergone three makeovers, including the use of more lively colors and a wind field circle that shows how far tropical storm, or hurricane-force winds extend.
Its size is realigned each year based on the average track errors from the previous five years, and so that the center of the storm stays inside the cone 66 percent of the time.
A smaller cone can mean fewer evacuations and less panic by narrowing the amount of land it looms over.
“I use it to see if I’m in immediate danger, but I know that just because I’m not in the cone, doesn’t mean I’m safe,” said Lake Worth resident Tom Serio, a disaster and recovery consultant. “Understanding the cone is really a part of living in Florida.”
National Hurricane Center meteorologists produced the most accurate storm track forecasts in 2017 since modern mapping of tropical cyclones began nearly 50 years ago. For every measurement, which includes days 1 through 5 before estimated landfall, the 2017 forecasts topped the hurricane center’s running five-year average by nearly 50 miles at the 120-hour mark.
In 2010, the mean track error at five days was 327 miles.
That was reduced to 225 miles for the error rate between 2012 to 2016.
In 2017, the five-day track error was about 180 miles.
“What’s happening is the five-day forecast today is almost as good as the four-day forecast in 2012,” said Jonathan Vigh, a project scientist at the National Center for Atmospheric Research. “So they have bought you almost an extra day.”
The reasons for the increased accuracy in forecasting the tracks of 2017’s 17-named storms are multiple.
Researchers and modelers have improved pieces of code that go into computer models representing processes in the atmosphere, such as radiation and clouds. Computers are running at higher resolutions, allowing them to represent finer details such as individual thunderstorms. And more sophisticated satellites circle the Earth, beaming down images so clear, forecasters see towering cloud tops and fields of Saharan dust like never before.
Also, track forecasting is easier than predicting the intensity of a storm because tropical cyclones are steered by large weather patterns that meteorologists can watch evolve. On the other hand, the interactions of water and air inside a hurricane that control wind speeds remain a mystery in many respects.
Predicting rapid intensification — an increase in wind speeds of 34 mph or more over a 24-hour period — is still a challenge. During the 2017 hurricane season, there were 39 incidents of rapid intensification but only seven were accurately forecast.
The Hurricane Forecast Improvement Project, which was launched after the storms of 2004 and 2005, is working on advancing intensity forecasts as well as track.
Further changes to the size and shape of the forecast cone are likely.
Michael Brennan, branch chief of the NHC’s hurricane specialist unit, said he’d like to custom fit cone sizes to each storm depending on the confidence in the forecast. Currently, each cone is the same size.
Substantially slimmer cones mean fewer watches and warnings along coastlines, said Jeff Masters, co-founder of Weather Underground.
“Since it costs roughly $1 million per mile of coast evacuated, this will lead to considerable savings, not only in dollars, but in mental anguish,” he said.
COMING SUNDAY, MAY 27, IN THE PALM BEACH POST
ARE YOU READY?
Our special hurricane section. A tracking map, evacuation zones and advice on how to prepare.