Hurricane category ratings can be misleading. Check out these deadly 'minor' storms.

On its way to the North Carolina coast, Hurricane Florence weakened, yet simultaneously meteorologists warned that it was becoming more dangerous. That might seem counterintuitive if you assume that the category system for hurricanes is based on severity. It’s not. It’s based on just one variable: wind speed.

But wind speed isn’t the only—or even the most important—variable in what makes a hurricane destructive. Part of the equation is, of course, where it hits. Plenty of hurricanes bluster through the middle of the Atlantic with little fanfare, since they’re far enough away that they don’t really affect us. And wind speed is, of course, a factor. But most of our most recent dangerous hurricanes have been all about water.

SEE: Photos of Florence's destruction: 

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Hurricane Florence makes landfall
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Hurricane Florence makes landfall
IN SPACE - SEPTEMBER 14: In this NOAA satellite handout image , shows Hurricane Florence as it made landfall near Wrightsville Beach, North Carolina on September 14, 2018. The National Hurricane Center reported Florence had sustained winds of 90 mph at landfall and was moving slowly westward at 6 mph. (Photo by NOAA via Getty Images)
MYRTLE BEACH, SC - SEPTEMBER 14: Storm clouds are seen over the 2nd ave pier as the force of Hurricane Florence is beginning to be felt on September 14, 2018 in Myrtle Beach, United States. Hurricane Florence is hitting along the North Carolina and South Carolina coastline bringing high winds and rain. (Photo by Joe Raedle/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: A car goes through a flooded street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
MYRTLE BEACH, SC - SEPTEMBER 14: Clouds are seen over a deserted Ocean blvd as the force of Hurricane Florence is felt on September 14, 2018 in Myrtle Beach, United States. Hurricane Florence is hitting along the North Carolina and South Carolina coastline bringing high winds and rain. (Photo by Joe Raedle/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: A car goes through a flooded street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: A flooded street is seen as the outer bands of Hurricane Florence hits in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: A car goes through a flooded street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: People try cross the street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: A man tries to cross the street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: People try cross the street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: People try cross the street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: US military vehicle goes through a flooded street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
NORTH CAROLINA, USA - SEPTEMBER 13: A man tries to cross the street during the heavy rain of outer bands of Hurricane Florence in New Bern, North Carolina, United States on September 13, 2018. Hurricane Florence is expected to arrive on Friday along the North Carolina and South Carolina coastline. (Photo by Atlgan Ozdil/Anadolu Agency/Getty Images)
People walk on a local street as water from Neuse River starts flooding houses upon Hurricane Florence coming ashore in New Bern, North Carolina, U.S., September 13, 2018. REUTERS/Eduardo Munoz
A member of the U.S. Army walks through floodwaters near the Union Point Park Complex as Hurricane Florence comes ashore in New Bern, North Carolina, U.S., September 13, 2018. REUTERS/Eduardo Munoz
Water from Neuse River starts flooding houses as the Hurricane Florence comes ashore in New Bern, North Carolina, U.S., September 13, 2018. REUTERS/Eduardo Munoz
The Bank of America is seen covered in plywood as the Hurricane Florence comes ashore in New Bern, North Carolina, U.S., September 13, 2018. REUTERS/Eduardo Munoz
Docks broken by water from Neuse River are seen floating as Hurricane Florence comes ashore in New Bern, North Carolina, U.S., September 13, 2018. REUTERS/Eduardo Munoz
The Union Point Park Complex is seen flooded as the Hurricane Florence comes ashore in New Bern, North Carolina, U.S., September 13, 2018. REUTERS/Eduardo Munoz TPX IMAGES OF THE DAY
Water from Neuse River floods houses as Hurricane Florence comes ashore in New Bern, North Carolina, U.S., September 13, 2018. REUTERS/Eduardo Munoz
MYRTLE BEACH, SC - SEPTEMBER 14: Linda Stephens checks out the weather as the force of Hurricane Florence is beginning to be felt on September 14, 2018 in Myrtle Beach, United States. Hurricane Florence is hitting along the North Carolina and South Carolina coastline bringing high winds and rain. (Photo by Joe Raedle/Getty Images)
A tree bends from the heavy rain and wind from Hurricane Florence in Wilmington, North Carolina on September 14, 2018. - Florence smashed into the US East Coast Friday with howling winds, torrential rains and life-threatening storm surges as emergency crews scrambled to rescue hundreds of people stranded in their homes by flood waters. Forecasters warned of catastrophic flooding and other mayhem from the monster storm, which is only Category 1 but physically sprawling and dangerous. (Photo by ANDREW CABALLERO-REYNOLDS / AFP) (Photo credit should read ANDREW CABALLERO-REYNOLDS/AFP/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Volunteers from the Civilian Crisis Response Team help rescue three children from their flooded home September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
Jeremiah Johnson, a front desk clerk at the Sleep Inn in Jacksonville, North Carolina, attempts to reattach the front doors of the hotel on September 14, 2018, after the hotel lost power in the evening during Hurricane Florence. - Florence smashed into the US East Coast Friday with howling winds, torrential rains and life-threatening storm surges as emergency crews scrambled to rescue hundreds of people stranded in their homes by flood waters. Forecasters warned of catastrophic flooding and other mayhem from the monster storm, which is only Category 1 but physically sprawling and dangerous. (Photo by Logan Cyrus / AFP) (Photo credit should read LOGAN CYRUS/AFP/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Volunteers from the Civilian Crisis Response Team rescue a man with chest pains from his flooded home September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Volunteers from the Civilian Crisis Response Team help rescue three children from their flooded home September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Volunteers from the Civilian Crisis Response Team help rescue three children from their flooded home September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Volunteers from the Civilian Crisis Response Team help rescue three children from their flooded home September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
The roof of a house is seen affected by winds from Hurricane Florence as it hits the town of Wilson, North Carolina, U.S., September 14, 2018. REUTERS/Eduardo Munoz
Children sit and play games in a hotel lobby that has lost its power as Hurricane Florence comes ashore on Wilmington, North Carolina, U.S., September 14, 2018. REUTERS/Carlo Allegri
MYRTLE BEACH, SC - SEPTEMBER 14: A damaged awning is seen as winds from Hurricane Florence on September 14, 2018 in Myrtle Beach, United States. Hurricane Florence is hitting along the North Carolina and South Carolina coastline bringing high winds and rain. (Photo by Joe Raedle/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Rescue workers from Township No. 7 Fire Department and volunteers from the Civilian Crisis Response Team use a truck to move people rescued from their flooded homes during Hurricane Florence September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Rescue workers from Township No. 7 Fire Department and volunteers from the Civilian Crisis Response Team use a truck to move people rescued from their flooded homes during Hurricane Florence September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Volunteer Amber Hersel from the Civilian Crisis Response Team carries 7-year-old Keiyana Cromartie after she and her family were rescued from their flooded home during Hurricane Florence September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
JAMES CITY, NC - SEPTEMBER 14: Rescue workers from Township No. 7 Fire Department and volunteers from the Civilian Crisis Response Team use a boat to rescue a woman and her dog from their flooded home during Hurricane Florence September 14, 2018 in James City, United States. Hurricane Florence made landfall in North Carolina as a Category 1 storm and flooding from the heavy rain is forcing hundreds of people to call for emergency rescues in the area around New Bern, North Carolina, which sits at the confluence of the Nueces and Trent rivers. (Photo by Chip Somodevilla/Getty Images)
Rain water flooded streets are pictured as Hurricane Florence moves into the Carolinas in Wilmington, North Carolina, U.S., September 14, 2018. REUTERS/Roselle Chen
People walk in the rain water flooded streets as Hurricane Florence moves into the Carolinas in Wilmington, North Carolina, U.S., September 14, 2018. REUTERS/Roselle Chen
Palm trees blow in the wind as the outer bands of Hurricane Florence make landfall on September 14, 2018 in Myrtle Beach, South Carolina. - Florence smashed into the US East Coast Friday with howling winds, torrential rains and life-threatening storm surges as emergency crews scrambled to rescue hundreds of people stranded in their homes by flood waters. Forecasters warned of catastrophic flooding and other mayhem from the monster storm, which is only Category 1 but physically sprawling and dangerous. (Photo by Alex Edelman / AFP) (Photo credit should read ALEX EDELMAN/AFP/Getty Images)
Mitchell Floor, left, holds a flashlight as Comfort Suites general manager Beth Bratz, center, and employee Dee Branch go to make coffee as Hurricane Florence rages in Wilmington, N.C. Thursday Sept. 14, 2018. The area lost power around 4 a.m. and the facility was running small lights, phone chargers and the coffee machine on a generator. (Chuck Liddy/Raleigh News & Observer/TNS via Getty Images)
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Storm surges—when the ocean rises rapidly due to changes in pressure around it—are, in part, driven by wind speed, but they’re more directly determined by how large the cyclone is. Some storms may have 135 mile per hour winds, enough to be a Category 4 system, but the area in which the wind reaches that speed may be small. Conversely, a hurricane with slower winds that covers a much larger area is likely to do more damage. Take Hurricanes Ivan and Dennis. These Category 3 storms hit roughly the same part of the Gulf Coast one year apart. Dennis, which struck in 2005, caused approximately $2.2 billion in damage. One year before, Ivan had caused $14.2 billion. When meteorologists analyzed the differences between these two storms, they found that Ivan caused more than six times the damage because it covered five times the area, and thus could last much longer over land. This means a greater swatch of the U.S. experienced hurricane-force winds and torrential rain for longer periods of time.

That’s reminiscent of what made Harvey such a destructive storm for Houston: instead of moving quickly, it stalled over the area, dumping unprecedented volumes of water. That’s also what meteorologists are predicting will happen with Florence.

Total destruction, both in terms of dollars and casualties, also has to do with the population density of the area and the infrastructure in place. Katrina, of course, became a much more deadly storm when the levees failed in New Orleans, which at the time had 450,000 residents. All these factors contribute to how loose the correlation is between hurricane category and destruction.

hurricane destruction

Note this list is incomplete, since it only goes through 2017

The graph above comes largely from a single report analyzing all hurricanes from 1900-2010, in which researchers at the National Oceanic and Atmospheric Administration worked out what made certain storms particularly destructive. They found that the vast majority of the deadliest cyclones were of at least Category 3, but only a third were at 4 or above. (Part of that has to do with the fact that Category 4 and 5 storms are more rare). They also discovered that a lot of the costliest storms in terms of damage occurred as a result of inland flooding due to rain, whereas high death tolls were mostly the result of large storm surges. Hurricanes like Katrina, which have storm surges around 10 feet or more, kill large numbers of people who simply cannot fight the rushing waters.

hurricane destruction

A detailed view of the chart above

Infographic by Sara Chodosh

Troublingly, the researchers also noted how likely people are to ignore evacuation orders, thinking they can outlast the storm. “Sociologists estimate, however, that people only remember the worst effects of a hurricane for about seven years,” they wrote, and that even if they did remember, other researchers have estimated that “85% of U.S. coastal residents from Texas to Maine had never experienced a direct hit by a major hurricane.” This is largely because these coastal areas have experienced high population growth.

Inexperienced and experienced coastal-dwellers alike might do well to watch this clip from the National Weather Service, which shows what storm surges actually look like.

Unfortunately, researchers note that even increased awareness isn’t enough to prevent hurricanes from becoming more costly and deadly. “Continued coastal growth and inflation will almost certainly result in every future major landfalling hurricane (and even weaker hurricanes and tropical storms) replacing one of the current costliest hurricanes. For example, all three of the U.S. hurricane landfalls of 2008 made the top 30 list, despite none of them being major hurricanes at landfall.” As long as people build and live along the coast, we’ll have high death tolls and repair costs, especially since hurricanes are likely to become more intense as climate change progresses. Hurricanes are not just big, exciting rainstorms. They’re dangerous—even if they’re only a Category 1 or 2.

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