As storm forecasters have grown more certain over the years about the potential path a hurricane will take, the popular "cone of uncertainty" used in models has grown smaller. But widespread misunderstanding of the cone has prompted forecasters to try to improve the tool.
This year the National Hurricane Center will use a modified tool with an even sleeker tracking cone and an advancement they hope will help people not directly in a storm's path better understand the potential danger they face.
A shaded area overlaid beyond the cone will show the farthest reaches of possible tropical storm- and hurricane-force winds.
"The public tends to still focus on the exact path of the storm (based on the cone) and they don't take into account the stuff that happens outside of it," said Stacy Stewart, senior hurricane specialist at NOAA's National Hurricane Center in Miami. "The wind field is much larger than the cone. We're using that to give people an idea of wind hazards that exist outside the cone."
The improved tool is an attempt to alert folks not to let down their guard if they're not precisely in the direct path of a storm.
"People think, 'I'm outside the cone, so I'm going to be okay,' " said Betty Hearn Morrow, professor emerita in sociology at Florida International University, who has helped research and test National Weather Service tools. But that's not always the case, she said, because the cone doesn't account for dangerous winds. The new map is "the right idea, definitely," she said.
Stewart said people should also remember that the cone is still a flawed predictor. One-third of the time the center of a hurricane will travel outside of the cone completely.
"Thirty-three percent of your forecast can still fall outside the cone," he said.
The National Weather Service has unveiled several other new tools aimed at precisely conveying potential hazards like storm surge and wind speed.
A storm surge watch/warning system will be used this hurricane season to highlight areas along the Gulf and Atlantic coasts that are at risk of life-threatening inundation. The new tool would alert residents to the risks of rising water and the need to evacuate.
"Along the coastline, storm surge tends to be the primary killer of people," Stewart said.
The weather service will also roll out an experimental map that predicts the time of arrival of tropical-storm-force winds. Using a wind-speed-probability model in which 1,000 plausible scenarios are calculated, the graphic will display the earliest reasonable and most likely arrival time of storm winds on land, giving people an idea of how long they have to prepare for a storm.
Another change: Hurricane forecasters are now allowed to issue advisories for what they are calling "potential tropical cyclones." Before, they had to wait until a storm was more developed before issuing warnings and a projected path. Now, they can issue advisories for any storm systems that pose a threat of tropical-storm or hurricane-force winds to land within 48 hours.
"Advances in forecasting over the past decade or so … now allow the confident prediction of tropical cyclone impacts while these systems are still in the developmental stage," the weather service wrote in its description of new products for the 2017 hurricane season, which begins June 1 and runs through the end of November. "For these land-threatening 'potential tropical cyclones', (the National Hurricane Center) will now issue the full suite of text, graphical, and watch/warning products that previously has only been issued for ongoing tropical cyclones."
Contact Ben Montgomery at [email protected] or (727) 893-8650. Follow @gangrey.