Hurricane categories consider windspeed but ignore one of the deadliest effects
Dennis Mersereau
at 08:11 AM Oct 9 2018
Hurricane categories consider windspeed but ignore one of the deadliest effects
Florence creeps her way up to the coast.
NOAA
Nature // 

The Saffir-Simpson Scale isn't working, but we can't abandon it.

 

One of the scariest things you can hear before a hurricane hits is that someone won't evacuate because the storm hasn't hit a certain category yet. Coastal residents' over reliance on the Saffir-Simpson Hurricane Wind Scale is a dangerous prospect when a storm makes landfall. Hurricane Florence is the latest example of a storm that vastly over-performed its category on the scale. It made landfall as a category one, but that bottom-of-the-scale ranking doesn't come close to describing the destructive storm surge or historic rainfall left in its wake. How do we fix the disconnect between a storm's perceived strength and its actual hazards? It's a tough call, and, unfortunately, it may not be possible to ditch the wind scale and start over.

The inevitable post-Florence debate among meteorologists and emergency managers included talk of scrapping the Saffir-Simpson Scale. As a weather reporter who's spent years trying to talk about threatening hurricanes, I don't think that's entirely possible. The categories we use to describe wind strength in hurricanes is too deeply ingrained in the weather education of the United States to be able to completely remove it from the discussion. We have to work with the scale so that people in harm's way pay proper attention to the winds, but also focus on the hazards posed by heavy rain and storm surge.

Developed by engineer Herbert Saffir and former Director of the National Hurricane Center Robert Simpson, the Saffir-Simpson Hurricane Wind Scale came about in the early 1970s to help meteorologists convey the destructive potential of a hurricane. Each category from one to five describes a new degree of potential damage in the areas that experience a storm's highest sustained winds. A category one hurricane would produce superficial damage to a well-built home—breaking windows, gutters, and shingles—while the strongest winds of a category five hurricane would make rubble of even a sturdy structure.

This scale doesn't always accurately describe the threat posed by storms. The majority of people who die in landfalling storms drown as a result of a storm surge or freshwater flooding from heavy rain.

Hurricane Florence was “only” a category one when it made landfall in North Carolina on September 14, 2018, but the hurricane's large wind field brought a magnitude of storm surge flooding to the coast typically seen in a storm with much higher winds. Even worse, interior sections of North Carolina saw devastating flooding after the slow-moving storm produced up to three feet of rain in the days after landfall.

There are countless examples of storms that had effects much greater than their maximum sustained winds would suggest. Hurricane Ike, which devastated southeastern Texas in 2008, made landfall with the winds of a category two storm, but its size drove a storm surge greater than 20 feet deep into parts of the coast. Hurricane Katrina was a category three hurricane at landfall in Louisiana and Mississippi, but its size and former strength produced a storm surge you'd expect to see in a scale-topping storm.

Hurricane Harvey made landfall as a category four near Corpus Christi, Texas, in August 2017, leaving behind extensive wind damage where the eye came ashore. But Harvey drenched southeastern Texas and Louisiana for days after it weakened to a tropical storm, bringing about unprecedented rains and flooding, including an astounding five-foot rainfall total near Beaumont, Texas.

Still, while the greatest threat to life in a landfalling hurricane is from drowning, we cannot discount the effects of winds. Entire neighborhoods saw total devastation after the 165 MPH winds of Hurricane Andrew made landfall in southeastern Florida in August 1992. Flying debris, falling trees, and building damage can seriously injure or kill people if they're not properly protected. Strong winds over soggy soil can lead to extensive power outages along the path of a landfalling storm, even far inland from the coast. More than a million people across the Carolinas lost power at one point during Hurricane Florence. The lingering effects of wind damage can prolong suffering for many days and weeks.

So how do we effectively broadcast a storm's true threat level? Theories pop up after every big storm. Some meteorologists think we should scrap the system entirely and try to wean people off of thinking of storms in terms of categories at all. Others think it's worth exploring a way to replace the existing scale with a complex formula that accounts for winds, storm surge, and expected rainfall totals, indexing all those factors into a standardized value. Another (likely-confusing) possibility is creating separate scales to characterize each individual hazard. Meanwhile, the growing intensity of storms in general has some arguing that, should we continue to use the wind scale, we should add a sixth category to reflect higher maximum wind speeds.

But the best course of action is likely to downplay the scale while talking-up the non-wind threats of a storm. Meteorologists did a fantastic job getting the word out that the biggest threat in Florence was the flooding. Even so, some coastal residents opted to stay—or even went back home—after hearing that the storm's winds had weakened a bit while Florence made its final approach. Many of those people found themselves stranded for days without power as most of the roads in and out of the area were later severed by flooding.

It would take generations to train ourselves not to think of hurricanes in terms of category strength. That leaves it up to us to recognize the strength of a storm's winds while also paying attention to its other hazards when they may pose the greatest threat to life and property. Meteorologists have to recognize the limitations of using categories to characterize storms and, just as they did during Florence, drive home the message that flooding can be even more dangerous. Improving weather forecasts is a team effort. A forecast is only successful when the people who need them can use them effectively.

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