Why even a record-breaking hurricane can't hit Category 6

Record-breaking and "potentially catastrophic" Hurricane Irma is smashing its way into the islands of the northeast Caribbean with sustained winds raging at up to 295 km/h.

The U.S. National Hurricane Center says it's the strongest hurricane on record in the Atlantic Basin (outside the Caribbean Sea and the Gulf of Mexico) and "will bring life-threatening wind, storm surge and rainfall hazards" to the northeastern Caribbean starting today.

Irma is currently listed as a Category 5 hurricane, but some articles circulating on the internet claim it could become the first to reach Category 6.

But those articles are fake.

How do we know? Because the Saffir-Simpson hurricane wind scale, which categorizes hurricanes' destructiveness based on their wind speeds, ranges from 1 to 5.

Category 3 hurricanes and above are considered major, and the worst storms are Category 5, encompassing all hurricanes with sustained winds of 252 km/h or more.

When a Category 5 storm hits, you can expect "catastrophic damage," according to a National Hurricane Center backgrounder. "Most of the area will be uninhabitable for weeks or months," it says, as the winds will destroy many homes, collapsing roofs, walls, trees and power lines, causing power outages that last for weeks or months.

But why is there no Category 6?

"Because once you say catastrophic and there's near complete damage, why do you need a 6?" says Dennis Feltgen, a spokesperson for the National Hurricane Center.

Of course, it's not wind speed alone that makes hurricanes destructive. Hurricane Harvey was just a Category 4 when it hit the coast of Texas on Aug. 25, but killed at least 60 people and left 560,000 families seeking housing assistance. Massive flooding from storm surges and more than a metre of rain caused much of the destruction.

"We basically have a scale for storm surge … how many feet above ground level there would be inundation." says Feltgen.

But the different factors that make storms destructive are too variable to measure on a scale of wind speed, he said.

Here's a list of the different hurricane categories and what they mean, according to the National Hurricane Center:

• Category 1 (119-153 km/h): Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.
• Category 2 (154-177 km/h): Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.
• Category 3 (178-208 km/h): Devastating damage will occur: Well-built frame homes may incur major damage or loss of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.
• Category 4 (209-251 km/h): Catastrophic damage will occur: Well-built frame homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
• Category 5 (252 km/h or higher): Catastrophic damage will occur: A high percentage of frame homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.