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Flying over the Atlantic Ocean at the beginning of last week, relying on the Carolinas, Hurricane Florence degenerated into a Category 4 storm, almost 5 – and this caught the attention of everyone. People know that a Cat 5 is as big as a storm.
In Craven County, North Carolina, authorities changed their voluntary evacuation order to "mandatory" for all 105,000 residents.
Then Florence encountered sheared winds and demoted to Cat 3 – and then Cat 2.
It also caught everyone's attention. In Craven County, thousands of residents have decided to stay put. Many regretted this decision when the storm threw water on the Neuse River and on its banks, flooding the historic city of New Bern. About 1,300 people had to be saved, some of the roofs of their homes or cars.
"A lot of people have stayed because the storm has gone from category 4 to category 2, and they think that figure is the end," said Amber Parker, the county's chief of information.
Florence was only a Category 1 storm when she landed on the beaches of North Carolina. But no one in the Carolinas thinks today in Florence like a little hurricane – "just a 1."
Hurricane categories are determined by the Saffir-Simpson wind scale, which was used by the National Hurricane Center for decades. There is now a heated debate over whether the scale is overused or needs to be replaced.
The greatest virtue of the scale is that it is easy to understand.
"It's simple in a stressful world," said Chia-Ying Lee, a researcher at Columbia University studying hurricane risk. But a more complete threat note for Florence could have made it a category 4 or 5, said Lee.
The central problem of the Saffir-Simpson scale is that, as clearly indicates its full name, it measures only the wind. It does not capture threats such as coastal storm surges and heavy rains or does not talk about the size of a hurricane.
"It's almost like they need a new code system. Category 1 hurricane and "something" category for precipitation, "said Corinne Cutler Corr, a resident of New Bern who chose not to evacuate. She and her husband, an entrepreneur, live on relatively high land and thought they could help their neighbors who were riding her.
Bill Lapenta, director of the National Environmental Prediction Centers, said the national weather service warned residents of Florence of the probability of record rainfall, catastrophic floods and a potentially deadly storm surge. However, he predicted, Florence will encourage the scientific community to discuss how to describe the threats caused by hurricanes.
"We are increasingly sensitive to the need to communicate clearly," he said.
Gina Eosco, who works for the Cherokee Nation's strategic programs and specializes in weather risk communication, will note that the wind will always dominate the public impression of a hurricane at the start of the season. First impressions persist, she says.
"If you consider a hurricane as a chapter book, the first chapters, the main character may be the wind. But as the story evolves and we get a better idea, the story changes and new characters come into play, "she said. "The problem is that some people continue to focus on the first chapter."
Taylor Fontenot, captain of a group of volunteers known as the Navy Cajun of America, ran to help those affected by the Florence disaster. Then people feel that they are fine. It is at this moment that we get the scenarios of life and death.
Another useless phenomenon is the suspicion that experts and media mediate a storm.
"Alarmist media again. Florence overestimated. Descend two notches to Cat 2 already. Soon the first cat. They are still trying to tease, "Pennsylvania state legislator Rick Saccone said on Twitter.
Nobody has produced a widely accepted metric to replace Saffir-Simpson. Creating such a thing can be impossible, even imprudent.
"I'm not a fan of the Saffir-Simpson scale or any attempt to characterize a single-digit hurricane," said Massachusetts Institute of Technology professor of atmospheric science, Kerry Emanuel. "In my opinion, there is no substitute for a succinct statement of the threat of a particular storm."
The rating of a storm on the Saffir-Simpson scale often underestimates the destructive power of the storm. A classic example is Sandy, who barely had hurricane force winds when he hit New Jersey and New York in October 2012 and caused tens of billions of dollars in damage. A year earlier, Hurricane Irene was reduced to a tropical storm on arrival in the same region and had generated record floods.
A very large storm with a relatively low wind speed can produce a monster storm wave. This was the case with Hurricane Ike in 2008, which blew from the Gulf of Mexico Ike's deadly storm surges destroyed the water gauges at Galveston, but research has found that water levels at high tide have risen 20 feet.
Rain is the most underrated hurricane threat. Last year, Hurricane Harvey was a Category 4 storm near Corpus Christi, Texas, but wind damage proved to be a rounding error along the coast. . This is a reminder of the June 2001 floods caused by a storm as slow as that of Cat 1 – Tropical Storm Allison.
Perhaps the most important factor in the destructive potential of a hurricane is the vulnerability of places and people in its path. Much of the population of New Orleans lived below sea level when Hurricane Katrina hit in 2005. Houston had a massive population living in areas prone to flooding. And Puerto Rico experienced economic and infrastructural problems when Hurricane Maria hit the island territory last September.
In Maria's case, the category 4 designation accurately captured the immediate destructive power of the storm. But the ensuing humanitarian disaster – officially attributed 2,975 deaths in six months – was out of reach.
"I do not think the Saffir-Simpson scale is useful. In fact, I think this can be misleading in representing the risk of a storm. Perhaps it should be abandoned, "said Isaac Ginis, professor of oceanography at the University of Rhode Island.
Ginis used a grant from the Department of Homeland Security to develop a computer tool that creates 3D images of the potential damage caused by hurricanes. For example, a Category 3 hurricane resulting in a 20-inch drop of rain would have catastrophic consequences for Providence, RI, if the hurricane barriers in the bay had been raised to block the storm surge, was -he adds. Downtown Providence would essentially become a lake fed by two rivers, he added.
Among those who are not ready to dump Saffir-Simpson is Brian McNoldy, an associate researcher at the Rosenstiel School of Marine and Atmospheric Science at the University of Miami and author of a hurricane blog.
"I do not see an obvious replacement," he said.
For starters, any scale describing the threats to the earth would not be enough to describe a hurricane on the high seas – where, for example, there is no storm surge and precipitation is irrelevant. The ocean can not be flooded.
A possible complement to the Saffir-Simpson scale would be that based on integrated kinetic energy. This is a measure of the power of the winds across the width of the tropical cyclone. A storm like Florence would have a high IKE rating because it was a big storm – a storm that grew as it approached the land – with powerful winds that extended 200 miles eyes.
But the IKE did not say anything about the wind speeds. Residents of South Florida who suffered from Hurricane Andrew in 1992 can attest that a Cat 5 storm is a different animal than cat 1. Andrew, a compact hurricane, had winds that, according to one 2004 analysis, reached 167 miles at the time.
A wind scale and a global energy scale would still not talk about precipitation. And with Florence, the rain was the story.
"It would have been a 5 on the precipitation scale," McNoldy said.
Jason Samenow and Angela Fritz contributed to this report.
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