What Do Hurricane Categories Mean?
Hurricane categories come from the Saffir-Simpson Hurricane Wind Scale, which rates storms 1 to 5 by maximum sustained wind only. Category 1 is 74 to 95 mph and Category 5 is 157 mph or higher. Categories 3 through 5 are major hurricanes. The scale says nothing about storm surge, rainfall, flooding or storm size.
You will hear it every hurricane season: "Oh, it's only a Category 1." Please don't be that person. The category number is useful, but it measures one thing. The white cone on the forecast map is useful too, and it is probably the most misread graphic in weather. Let's fix both.
Key Takeaways
- The Saffir-Simpson scale rates hurricanes 1 to 5 using maximum sustained wind only.
- Category 3, 4 and 5 storms are major hurricanes, starting at 111 mph.
- Wind force grows roughly with the square of wind speed, so damage climbs steeply.
- The cone shows where the storm's center will likely go, not how big the storm is.
- The center leaves the cone about one-third of the time, and impacts reach far outside it.
Two of the most familiar graphics in weather are the hurricane category number and the white forecast cone. Both are useful, and both are often misunderstood. This lesson explains what each one actually says, and just as important, what it does not.
What Is the Saffir-Simpson Hurricane Wind Scale?
The Saffir-Simpson Hurricane Wind Scale rates hurricanes from 1 to 5 based only on their Maximum Sustained Wind, the highest 1-minute average wind at 10 meters above the surface. It was developed in the early 1970s by engineer Herbert Saffir and meteorologist Robert Simpson, and in 2010 the National Hurricane Center simplified it into a pure wind scale.
The Categories
- Category 1: 74 to 95 mph. Very dangerous winds that will produce some damage: roof shingles, gutters and siding, large tree branches snapped, power outages that may last days.
- Category 2: 96 to 110 mph. Extremely dangerous winds: major roof and siding damage on well-built homes, many shallow-rooted trees uprooted, near-total power loss lasting days to weeks.
- Category 3: 111 to 129 mph. Devastating damage: well-built homes may lose roof decking and gable ends, many trees down blocking roads, electricity and water unavailable for days to weeks.
- Category 4: 130 to 156 mph. Catastrophic damage: homes can lose most of the roof and some exterior walls, most trees and power poles down, areas isolated, outages lasting weeks to months.
- Category 5: 157 mph or higher. Catastrophic damage: a high percentage of framed homes destroyed, with total roof failure and wall collapse. Areas may be uninhabitable for weeks or months.
Major Hurricanes
A Major Hurricane is Category 3, 4 or 5. These storms account for a large share of hurricane wind damage in the United States, even though they are a minority of landfalls.
Why Wind Damage Rises So Fast
The force wind exerts on a structure goes roughly with the square of the wind speed. Going from 100 mph to 150 mph is a 50 percent increase in speed but more than double the force. Add in flying debris, which becomes more dangerous at higher speeds, and damage climbs steeply from category to category.
What Is the Difference Between Sustained Winds and Gusts?
The category uses the sustained wind. Gusts in a hurricane are usually 20 to 30 percent higher, and winds on the upper floors of tall buildings are stronger than at 10 meters. Winds are also often strongest in the right side of the storm relative to its motion, where forward speed adds to the rotation.
What Does the Hurricane Cone Mean?
The NHC forecast graphic shows a line of forecast center positions and a white Cone Of Uncertainty around it. Here is what the cone really means:
- The cone shows where the center of the storm is likely to track, not the size of the storm.
- It is built from the NHC's own historical track errors over the previous five years. Circles are drawn around each forecast point so that about two-thirds of past forecast errors fit inside.
- That means the center moves outside the cone about one-third of the time.
- The cone widens with time because forecast errors grow the farther ahead you look.
- Hazards such as wind, rain and surge regularly extend far outside the cone. Hurricane-force and tropical-storm-force winds may reach hundreds of miles from the center.
What Is the Difference Between a Hurricane Watch and Warning?
- Hurricane Watch: hurricane conditions are possible, issued about 48 hours before tropical-storm-force winds are expected.
- Hurricane Warning: hurricane conditions are expected, issued about 36 hours before tropical-storm-force winds arrive, since preparations become hard once those winds begin.
- Similar watches and warnings exist for tropical storm conditions and for storm surge.
Intensity Forecasting
Track forecasts have improved faster than intensity forecasts. The hardest events are rapid intensification, defined as an increase of at least 35 mph (30 knots) in 24 hours. Storms that rapidly intensify just before landfall are especially dangerous because people may have prepared for a weaker storm.
Real-World Example: Hurricane Michael, 2018
Hurricane Michael made landfall near Mexico Beach, Florida, in October 2018 as a Category 5, the first Category 5 landfall in the continental US since Andrew in 1992. It intensified rapidly over the Gulf of Mexico in the days before landfall. That is the scenario this lesson warns about: people can prepare for one storm and get a much stronger one.
Michael is also a good reminder that a category describes wind. Its surge, its wind damage far inland and its long power outages were all part of the story, and the NHC advisories spelled out each hazard separately. Read the whole advisory, not just the number.
Common Mistakes
- Myth: A Category 1 hurricane is no big deal. Fact: Category 1 winds are very dangerous and cause damage and multi-day power outages. A large Category 1 can also bring deadly surge and flooding, which the category does not measure.
- Myth: If I'm outside the cone, I'm safe. Fact: The cone only shows the likely path of the center. Wind, rain, surge and tornadoes regularly reach far outside it, and the center itself leaves the cone about one-third of the time.
- Myth: The cone shows how big the storm is. Fact: The cone's width comes from historical track errors, not storm size. It widens with time because forecast errors grow the farther ahead you look.
- Myth: The category includes storm surge and pressure. Fact: Since 2010 the scale is purely a wind scale based on 1-minute sustained winds at 10 meters.
Go Deeper: Why Damage Climbs So Fast
Wind pressure on a surface is proportional to air density times the square of wind speed. Double the speed and the force roughly quadruples. Going from a 100 mph Category 2 to a 150 mph Category 4 raises the speed by half but more than doubles the load on roofs and walls. Structures also fail in sequence: once a roof edge or a garage door gives way, wind gets inside and pushes outward, and the failure accelerates. Debris carried at higher speed carries much more energy, adding impact damage on top of pressure loads.
On the forecasting side, the cone is built from NHC official track errors over the previous five years. Circles are drawn around each forecast position so that about two-thirds of historical errors fall inside, then the circles are joined. Because it is a statistical envelope of the center's position, it says nothing about intensity or wind field size. Intensity forecasts have improved more slowly than track forecasts, and rapid intensification, at least 30 knots in 24 hours, remains the hardest problem.
Check Yourself
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1 What does the Saffir-Simpson scale measure?
Show The Answer
Maximum sustained wind speed Since 2010 it is purely a wind scale based on 1-minute sustained winds.
2 What is the wind range for a Category 3 hurricane?
Show The Answer
111 to 129 mph Category 3 is 111 to 129 mph and is the lowest category counted as a major hurricane.
3 What does the forecast cone represent?
Show The Answer
The likely track of the storm's center, based on past errors The cone contains the center's track about two-thirds of the time, and impacts often extend outside it.
4 About how often does a storm's center travel outside the cone?
Show The Answer
About one-third of the time The cone is sized to hold about two-thirds of historical errors, so roughly one in three tracks leave it.
Questions People Ask
What wind speed is a Category 5 hurricane?
157 mph or higher, measured as a 1-minute sustained wind at 10 meters. Category 5 damage is catastrophic, with a high percentage of framed homes destroyed.
How often does a hurricane go outside the cone?
About one-third of the time. The cone is sized so that roughly two-thirds of past forecast errors fall inside it.
What is rapid intensification?
An increase in maximum sustained winds of at least 35 mph (30 knots) in 24 hours. It is especially dangerous right before landfall.
When are hurricane warnings issued?
A Hurricane Warning is issued about 36 hours before tropical-storm-force winds are expected, and a Hurricane Watch about 48 hours before. Preparations get hard once those winds begin.
Are gusts stronger than the category wind speed?
Yes. Gusts in a hurricane are usually 20 to 30 percent higher than the sustained wind, and winds on upper floors of tall buildings are stronger than at 10 meters.
Learn More From The Experts
- Saffir-Simpson Hurricane Wind Scale National Hurricane Center
- Definition of the NHC Track Forecast Cone National Hurricane Center
- Hurricane Safety NOAA / NWS
The number is the headline. The advisory is the story. Read the story. Jen — Jen
