Hurricane categories tell only part of the story — here’s the real damage storms like Laura can do

• Hurricane categories are determined by a storm’s wind speed, which doesn’t take into account the destruction they can leave from rain, storm surge, and flooding.
• Category 1 hurricanes and tropical storms can still have devastating impacts on the communities they hit, leaving power outages, downed buildings and trees, and long-term damage in their wake.
• Hurricane Laura went from a tropical storm classification to a Category 3 storm, and it’s forecast to strengthen to a Category 4 before it strikes Louisiana and Texas.
• These photos show the differences between hurricane categories, using memorable storms as examples.
• Visit BusinessInsider.com for more stories.

Hurricanes Irma and Harvey were two very different storms.

While Harvey’s record rainfall drenched southeastern Texas and western Louisiana in 2017, flooding Houston in over 4 feet of water, Irma’s winds flattened buildings, trees, and power lines on the Caribbean islands it devoured.

At its peak, Harvey was a Category 4 hurricane on the Saffir-Simpson scale, but its weakened winds downgraded it to a tropical storm the day after it made landfall. Irma was a Category 5 monster that was one of the strongest Atlantic hurricanes ever recorded. Both had widespread devastation even though they were on the opposite ends of the category scale.

Hurricane Laura is a Category 3 storm expected to be upgraded to a Category 4 before it strikes the US Gulf Coast Wednesday night. The National Hurricane Center warns its storm surge of up to 20 feet could be “unsurvivable.”

Hal Needham, a hurricane scientist at Louisiana State University, explained on the weather site WXshift in 2017 that a storm's category doesn't fully convey how much damage it could cause.

"Hurricanes and tropical storms throw three hazards at us: wind, rainfall, and storm surge," he wrote. "Think of the impacts separately. Storms with weaker winds are more likely to stall and dump heavier rainfall. This shocks people, as it would seem intuitive that a Category 5 hurricane would tend to dump more rain than a Category 1 hurricane. But the opposite is true."

Here's a closer look at the type of damage that storms like Hurricane Laura can cause.

The Saffir-Simpson hurricane scale, which does not include lower-level tropical storms or tropical depressions, is based solely on maximum sustained wind.

Once a tropical storm's winds exceed 39 mph, the storm gets a name. Most storms that make landfall in the US are tropical storms, not "major" hurricanes of Category 3 and above.

But "storms are too complex to define by one number," Needham wrote. While Harvey's strong winds on the Texas Gulf Coast caused widespread destruction, most of the devastation came after it was downgraded to a tropical storm, dumping feet of water on Texas and Louisiana.

Source: WXShift

While strong winds can rip shingles off roofs and tear down power lines, flooding often causes more widespread, costlier damage — and can be more dangerous for humans, no matter what the hurricane category is.

Harvey, for example, was particularly devastating because it stalled over the Houston area, staying in roughly the same place for five days.

Category 1 hurricanes have wind speeds of 74 to 95 mph. They can damage a home's exterior, break large tree branches, and knock down power lines, causing multiday power failures. Hurricane Dolly was this rating when it hit Texas in 2008.

Source: Insider

Category 2 hurricanes have wind speeds of 96 to 110 mph. Storms of this intensity can cause major damage to homes and uproot large trees. They also generate power failures that last up to weeks. Hurricane Ike was a Category 2 when it hit Texas in 2008.

While a hurricane's category classifies how strong it is, this definition can't fully predict how devastating it might be. Superstorm Sandy hit Category 3, but by the time it made landfall in New York and New Jersey in 2012 it had weakened to a post-tropical cyclone.

Category 3 storms have wind speeds of 111 to 130 mph. But with Sandy, the storm surge, or rise in sea level, did some of the worst damage. It reached nearly 8 feet in parts of the Jersey Shore and 6 1/2 feet around New York City. Its "superstorm" status was because it was so wide — up to 1,000 miles across.

Hurricane Katrina in 2005 was the most devastating storm ever to hit the US. It killed 1,833 people and caused $108 billion in damage, though it was technically a Category 3 when it made landfall in Louisiana with sustained wind speeds of 125 mph.

Category 4 hurricanes have wind speeds of 131 to 155 mph, uprooting most trees and creating power failures that can last weeks or even months. Hurricane Charley was a Category 4 when it made landfall in Florida in 2004.

Hurricane Maria was a Category 4 storm when it made landfall in Puerto Rico in 2017, leaving 100% of the island without power. Parts of the US commonwealth are still recovering from the hurricane two years later — 30,000 homes have tarps for roofs.

Sources: AP, Insider

Hurricane Andrew was one of the strongest storms ever to make landfall in the US. It was a Category 5 hurricane when it hit Florida's Dade County in August 1992.

Category 5 storms have wind speeds greater than 156 mph, which can destroy most framed homes, cause power failures, and leave areas where it hits uninhabitable for weeks or even months. Irma was a Category 5 storm when it "totally demolished" the island of Barbuda in 2017.

Source: Business Insider

Local weather stations there captured wind gusts of 155 mph before going silent, indicating that the instruments had been blown away. The destruction was so severe that the island was initially cut off from communication, and 90% of its buildings were destroyed.

Source: Business Insider

Hurricane Irma was so powerful that it could have been considered a Category 6 storm. Theoretically, if we extended the Saffir-Simpson scale, Irma would be a Category 6, with wind speeds of 175 to 195 mph. It ended up making landfall in Florida as a Category 4, knocking out power for 6 million people.

Source: Business Insider

The problem with extending the Saffir-Simpson scale is that it's also a measurement based on destruction, and Category 5 storms typically destroy buildings and utilities. Technically, categories above 5 wouldn't cause more damage because there's no more damage to be done.

Whether a storm is a theoretical "Category 6" or a tropical storm, its impact for people in its wake can be devastating.

Part of the issue is that climate change is causing ocean and air temperatures to rise, which is making hurricanes more sluggish, giving them more time to suck up water and gain strength.

Sources: Insider, Nature

On Wednesday afternoon, Hurricane Laura was heading toward Louisiana and Texas as a Category 3 storm, threatening the Gulf Coast with maximum sustained winds of 125 mph, storm surge up to 20 feet, and up to 15 inches of rain.

Sources: NHC, Insider

The NHC expects Laura to strengthen to a Category 4 hurricane before it makes landfall late Wednesday night. It's been sucking up warm water in the Gulf of Mexico. While its wind speed could be devastating, the NHC warned Laura's storm surge could be "unsurvivable."

Sources: NHC, Insider