A storm undergoing rapid intensification, as Hurricane Lee is now, can throw a wrinkle into the plans of emergency managers throughout North Carolina, forcing them to make choices about how to use the limited hours before such a storm makes landfall.
Part of the problem coastal states like North Carolina face with rapid intensification is residents who have experienced numerous storms and developed their own calculus for when to stay and when to flee. A storm that suddenly gains strength introduces an unexpected variable to the risk equation, potentially too close to landfall for people to change their minds about how to keep themselves safe.
Hurricane Lee has undergone dramatic rapid intensification this week. The National Hurricane Center wrote Thursday night that Lee had “skyrocketed” to Category 5 wind speeds, jumping from about 100 mph at 11 a.m. Thursday to about 160 mph at 11 pm.
“Particularly for the Carolinas — the Outer Banks and those coastal areas — the biggest risk has always been a storm coming in that for many people doesn’t warrant much concern and it intensifies rapidly and it gets inside of their ability to prepare and evacuate,” Craig Fugate, a former FEMA administrator, told The News & Observer.
Rapid intensification happens when a storm’s wind speeds increase by at least 35 mph over a daylong period. If a storm undergoes that process as it nears North Carolina’s coastline, emergency managers like New Hanover County’s Steven Still would be forced to make tough choices.
In such a scenario, Still said, it would be difficult to evacuate thousands of people with a storm bearing down on them. The fear is that many people would be unable to get out of harm’s way before the storm arrives. Still pointed to Hurricane Harvey in Texas in 2017, where many people drowned either in or trying to escape their cars.
Instead of trying to evacuate everyone, Still said, New Hanover County’s plan in such a scenario would be to focus on the storm surge, the relentless rising water that a storm brings ashore. People in the path of that storm surge would be directed to evacuate, while many others in the county would be directed to shelter in place until the hurricane passes.
“The evacuation out of an abundance of caution is not always the best method. (With) a targeted evacuation, particularly if it’s a rapid intensification, we’re really going to have to narrow down the numbers to those vulnerable to that highest impact,” Still said.
Will Ray, North Carolina’s emergency management director, said the state tries to envision the worst case scenario.
Hurricane Idalia, for example, underwent rapid intensification shortly before making landfall but did not look like it was going to be a major storm for North Carolina. Still, the state still activated 120 members of the National Guard and deployed two swift water rescue teams.
Like New Hanover County’s Still, Ray said a storm that rapidly intensifies could mean emergency managers don’t have as long as they’d like to prepare.
“Decisions on evacuations, decisions on sheltering, decisions on other things are going to have to be done probably much quicker than our ultimate timelines would like us to do,” Ray said.
Warm oceans are heat engines
Hurricane Lee is still churning through the Atlantic, and the Hurricane Center has consistently maintained that it is too soon to know how or where it could impact the East Coast. Rip currents are one likely effect, with the Hurricane Center warning that beachgoers could start seeing them as soon as Sunday.
Jason Sippel, a meteorologist with the National Oceanic and Atmospheric Administration’s Hurricane Research Division, said rapid intensification requires a few ingredients.
Those include warm ocean waters, a moist atmosphere to prevent thunderstorms from pushing cold air down to the surface and low vertical wind shear. Low wind shear means winds at different levels of the atmosphere aren’t blowing strongly in different directions.
A storm that’s undergoing rapid intensification is also likely to be smaller, Sippel said, comparing it to ice skaters spinning with their arms out and gaining momentum as they tuck their arms toward their body.
“In terms of a hurricane, that means the vortex is intensifying, it’s spinning more and more quickly. Imagine a curve. It’s intensifying a little bit, then a little bit more and then it shoots up,” Sippel said.
Fugate pointed to 2018’s Hurricane Michael as a classic example of a storm that underwent rapid intensification at a dangerous moment. That storm leapt from a tropical storm to a Category 5 shortly before making landfall in Florida, killing 45 people and causing $25 billion in damage.
Warm waters — like the Gulf of Mexico and the Atlantic Ocean right now — mean that when a storm intensifies, it seems to stay strong, Fugate added.
“These are heat engines. So the more heat there,the more potential. If you don’t have other limiting factors, these storms are just going to get stronger and stay stronger for longer periods of time,” Fugate said.
A warm ocean is one factor in rapid intensification that is being altered by climate change. Ocean temperatures reached record highs this summer; NOAA and Columbia researchers have found warming temperatures reduce vertical wind shear; and a warmer atmosphere can hold more moisture.
A 2021 report from the Intergovernmental Panel on Climate Change said rapid intensification has “likely” become more common in recent decades and said researchers have “medium confidence” that manmade climate change could be a factor.
Sippel acknowledged that rapid intensification has increased since the 1970s and 1980s but said how much of that can be attributed to climate change remains an open question. The Atlantic Ocean seems to go through multi-decade periods with stronger storms, he added, having undergone one from the 1920s through the early 1950s before entering a more quiet period.
“We might find that out in the future that yes there is something that is a signal there, but I’m not confident enough at this point to say that that is indeed happening,” Sippel said.
Forecasters and emergency management officials alike say the National Hurricane Center has made great strides in forecasting storm intensities over recent hurricane seasons.
In 2022, Sippel said, the Hurricane Center’s margin of error on rapid intensification was about 17 mph. That’s down from about 35 mph as recently as 2017.
Sippel, who is part of NOAA’s Hurricane Hunters crew, said the planes have helped with the intensity forecasts by helping the models better understand how features of the storm’s vortex could impact intensification.
“The intensity of the storm and the size of the storm determines the storm surge, and that’s the most important thing to get right because that’s what kills people,” Sippel said.
The Outer Banks’ experience
Drew Pearson was just preparing to start at Dare County in 2014 when Hurricane Arthur jumped from a low pressure system to a Category 2 hurricane.
“For emergency managers, that event makes you think a little bit more,” Pearson, Dare County’s emergency management director, told The N&O.
Traditionally, Pearson added, emergency managers try to think about what they would need if a storm is going to be a category higher than projected. Now, he said, they might need to be more expansive.
“We need to think about the impacts from multiple categories higher now because of the changes in the ocean conditions that are there that warm waters and things like that could bring,” Pearson said.
Pearson said he urges people to be aware of the potential impacts of a storm ranging from the forecast surge to rip currents to the tornado risk. Those things all provide more information about specific hazards a system poses than the category alone.
Part of being prepared is urging people to keep their emergency kits stocked and updated, making sure they know where to head if an evacuation is called and how they would shelter in place if that becomes necessary. That’s important, Pearson said, because a storm that rapidly intensifies compresses the timeline people have to prepare or make decisions.
“If Lee does come to us, we’re going to have four, five, six days to get ready for it, to do the things that we need to do. It’s the ones that develop quickly where you have hours, not days,” Pearson said.
This story was produced with financial support from the Hartfield Foundation and the 1Earth Fund, in partnership with Journalism Funding Partners, as part of an independent journalism fellowship program. The N&O maintains full editorial control of the work.