The 5 hurricane categories, explained

It’s a number attached to every hurricane, crucial to emergency response teams and city officials to mobilize preparedness: the Saffir-Simpson Hurricane Wind Scale, characterized by five categories.

The scale only measures one component of a hurricane: the wind. Each category is divided by a range of wind speeds, estimating potential damage and impacts on properties.

This year, the National Oceanic and Atmospheric Administration predicted an above-normal hurricane season. Record-breaking warm water in the Atlantic has increased tropical storm and hurricane activity.

Five hurricanes have swept through the Atlantic this year. Before the season concludes at the end of November, the Atlantic may experience a total of six to 11 hurricanes. Three of the hurricanes so far this year were considered major — Category 3 or above — and NOAA predicts that there could be up to two more.

SCROLL TO CONTINUE

An imperfect scale

The scale used to include other impacts like storm surge ranges and flooding, but they were removed to reduce public confusion, according to the National Hurricane Center.

Now the wind is the scale’s strength — but also its weakness, said Gina Eosco, the division chief and social science expert at the Weather Program Office for NOAA.

“It ends up missing the myriad of other risks that are oftentimes more serious in a hurricane, such as storm surge,” she said.

Scientists and forecasters are still learning how individuals perceive and adjust to risks as threats develop during hurricanes, Eosco said. Some experts hypothesize that people anchor to the storm category and don’t adjust for other risks.

“It is very misleading because somebody may not evacuate for a tropical storm or a Category 1 hurricane, but we have seen time and time again that these storms have had a lot of impact,” said Jennifer Collins, a hurricane researcher at the University of South Florida.

Each storm has its own personality, and there isn’t always a direct correlation between category and damage. This means a Category 1 hurricane could be more devastating than a Category 3.

“A simple one, two, three, four, five scale is not sufficient to communicate the threat that a hurricane brings,” said Jeff Masters, a hurricane expert for Yale Climate Connections.

Here is other extreme weather that’s associated with a hurricane:

STORM SURGE

As a hurricane barrels across the open ocean, strong winds drive the water forward. Once the water reaches the shore, it combines with normal tides and creates the storm surge.

Storm surge is the leading cause of hurricane-related deaths in the United States, according to the National Weather Service.

“The Hurricane Center realized this is a problem because [the scale] didn’t speak to storm surge in particular — which is the threat that kills the most people from hurricanes — so they introduced a separate storm surge watch and storm surge warning product,” Masters said.

In some cases, storm surge is responsible for the most hurricane destruction.

Hurricane Ike made landfall as a Category 2 hurricane with walloping sustained winds of 110 mph in September 2008, with hurricane-force winds extending 125 miles from the center. But the wind wasn’t what caused the most damage. The storm had a surge of more than 20 feet, the largest storm surge on record for a Category 2 hurricane. Imagine rushing water the height of two basketball hoops stacked on top of each other barreling toward homes, cars and buildings.

The storm claimed 195 lives and resulted in $30 billion in damage. It wasn’t even considered a major hurricane.

RAIN AND INLAND FLOODING

Not to be mistaken with storm surge, the other main cause of flooding during a hurricane is rain.

While some inland communities assume they are spared from the wrath coastal communities endure, storm impacts can occur tens to hundreds of miles outside of the storm’s eye. During hurricanes, excessive amounts of rain cause streams and creeks to overflow their banks and clog storm drains and sewage systems, which results in devastating flooding.

Hurricane winds weaken as they move over land, but the torrential rains don’t stop. Inland cities, with vast amounts of concrete and impermeable surfaces, also have a high risk of excess runoff and flooding.

Hurricane Harvey made landfall in Texas as a Category 4 with maximum wind speeds surpassing 130 mph in August 2017. But by the next day, the hurricane fell to a Category 1 and eventually was considered a tropical storm.

Yet the storm wasn’t done. Instead of moving on, Harvey stalled over Texas for days. In the end, the slow-moving storm unloaded 33 trillion gallons of water along the Gulf of Mexico and became the second costliest storm in U.S. history. An unprecedented 60 inches of rain fell in Southeast Texas, producing devastating and deadly flash and river flooding, according to the Weather Service.

A year after Harvey, Florence made landfall as a Category 1 hurricane and brought destructive flooding across the Carolinas. Florence was responsible for the heaviest rainfall ever recorded from a tropical cyclone in both South Carolina and North Carolina, according to the Hurricane Center.

Twenty-two people died due to direct impacts from Florence — 17 deaths of them from inland flooding. Damage totals exceeded $20 billion.

Florence, which peaked as a Category 4 hurricane over the ocean, had been downgraded to a tropical storm when it dropped most of its rain.

TORNADOES

The last risk people worry about when thinking about hurricanes is tornadoes.

The severe spin from hurricane systems, coupled with atmospheric instability and wind shear, creates perfect conditions for tornadoes. Both hurricanes and tornadoes cause damage due to strong rotating winds, so it’s not surprising that a large rotating system could also produce twisters.

Tornadoes generally start within thunderstorms embedded in the outer rain bands of hurricanes, according to the Weather Service. But sometimes they form near the eyewall, which is the ring of destructive winds that surround the storm center.

In September 2004, Hurricane Ivan unleashed a damaging storm surge, inland flooding and powerful wind gusts spanning Alabama to Florida. But that wasn’t the end of its impact.

The Category 3 hurricane was most notable for its unprecedented tornado outbreak. About 120 twisters touched down from Florida to Pennsylvania — across nine different states — over the course of three days. Virginia alone experienced a record-breaking 38 tornadoes across the state.

Overall, the tornadoes from Ivan were responsible for eight deaths and 17 injuries, according to the Weather Service.

SIZE

The size of a hurricane matters. A larger hurricane will tend to produce a more severe storm surge as well as stronger winds and heavier rain over a larger area. But the storm category doesn’t take size into account.

One of the ways hurricanes expand is through a process known as an eyewall replacement cycle. During this process, the inner eyewall collapses as a much larger outer eyewall forms around it, often resulting in a bigger hurricane.

Not long before striking land last year, Hurricane Ian underwent an eyewall replacement cycle, enlarging the storm substantially. It made landfall as a Category 4 hurricane very close to where Hurricane Charley did at roughly the same intensity in 2004. But Ian was a much larger storm and thus had more severe impacts.

Ian’s catastrophic surge, record-breaking inland flooding and damaging winds propelled it to become the costliest hurricane in Florida’s history and the third-costliest hurricane in the United States, according to the Hurricane Center.

Here are some tips to help you stay safe this hurricane season: