Hurricanes are classified by their wind speed, but the damage they can do depends on so much more than that. A tropical storm or hurricane is assigned a category level based on the fastest one-minute sustained wind speed found anywhere in the storm. It doesn’t take any other factors into consideration.
See how this scale is only based on wind? In many ways, it’s like basing a ten course meal on just the entree. The fastest wind speed inside a storm is a good indicator of the storm strength, but it doesn’t tell the whole story. There are several other parts of a hurricane and factors that can make it more or less destructive.
HOW WIDE IS THE WIND FIELD?
A wider storm means more people are hit by more wind! If the hurricane-force winds are only seen close to the eye-wall it won’t do as much damage as hurricanes that have hurricane force winds reach out for dozens of miles from their center. Physically larger storms can usually produce more storm surge too. A wider storm will start pushing more ocean water than a petite storm. Look below at how Irma compares to Andrew in size. Irma would likely produce more surge, if they hit in the exact same place.
WHAT ANGLE IS IT GOING TO HIT LAND?
Storm surge is terrifying, and it can change drastically from town to town based on the angle a storm makes landfall. Subtle changes in how a storm slams into a shoreline can have big impacts on how much water is pushed from the ocean onto land. Two identical hurricanes coming ashore at different angles could mean a difference of “feet” in surged water from town to town. Storm surge is incredibly destructive.
WHERE IS IS GOING TO MAKE LANDFALL?
Obviously if a hurricane hits a big city it’s more likely to do damage. The bigger the city, the more buildings, houses and people at risk to high wind! Urban areas also have a harder time evacuating, meaning more people may choose to stay behind and risk danger in a storm. Flash flooding is usually a problem in cities too, since asphalt and concrete don’t drain water well.
HOW FAST IS THE STORM?
A fast moving storm make pack an initial punch, but often times it is the slow-moving hurricanes that can unleash massive damage. A slow moving hurricane means a band of high wind can rage on the same little town for dozens of minutes. It’s like enduring a tornado or high wind event over and over again, instead of just for a matter of seconds. Slow moving storms can dump massive amounts of rain. This is why Hurricane Harvey has gone down in history. It stalled over Texas for days dumping the most rain in CONUS history.
HOW WIDE IS THE WIND FIELD?
This was especially evident in Super Storm Sandy. If hurricane force winds hug the eye wall, then they aren’t really going to affect as many people. A storm with a massive wind field will slam into more people, and will be able to create more storm surge. Hurricane Patricia in 2016 was the second strongest tropical system ever measured on record! Sustained winds were clocked in at 215 mph! Even though is was incredibly strong, it’s wind field was physically tiny, only extending 35 miles from the center of the storm. So when Patricia made landfall (in a more rural area, too) it didn’t do an incredible amount of damage. The storm was also a fast-mover, too which meant the monstrous winds were very quick to arrive, but very quick to leave.
IS THE STORM UNDERGOING EYEWALL REPLACEMENT?
A strong hurricane will undergo a process known as eyewall replacement to maintain its strength. When this happens, a new eye will form on the outside of the old eye. It will steadily shrink until it replaces the old eye. When this happens, the inner eyewall will weaken as the new eye gains strength. If this happens right before landfall, it can lessen damage done on impact.
HOW WILL IT INFLUENCE FUTURE STORMS?
Hurricane Sandy became “Super Storm Sandy” after it merged with a mid-latitude cyclone. This massively increased the storm’s impact and sucked it back onshore into New England. Without the merge of these too storms, Sandy may have stayed out to sea. Instead the combination of storms extended the tropical storm force wind field to outward in diameter to some 943 miles, the biggest circulation of any tropical system on record. Feet of snow fell in the Appalachian mountains, and massive storm surge inundated New Jersey and the northeastern seaboard.