Hurricane Irma will be powerful when it strikes Florida, but it’s not a Category 6 storm. That’s because there’s no such thing.
Rumors quickly spread online this week that the massive storm prompted scientists to expand the Saffir-Simpson Hurricane Wind Scale to include a new category. Google even reported a spike in U.S. searches for terms related to “Category 6.”
But experts said that’s false.
“There is no Category 6,” said Dennis Feltgen, a National Hurricane Center spokesman, in an email.
Hoax debunking site Snopes.com traced the rumor back to a post from a doomsday blog about a Category 6 debate in the scientific community. Misconceptions about the nonexistent hurricane category spread further when the post was picked up by websites that falsely claimed Irma had been designated Category 6.
Why it’s false
The Saffir-Simpson scale was developed in 1971 as a simple way for NOAA’s National Hurricane Center to give the public a general idea of a storm’s strength.
The scale isn’t actually a scientific measure, though. It is based on wind speed to predict the level of a hurricane’s destruction, broken into categories 1 through 5.
“The top end of scale [Category 5] is reserved for a major hurricane with maximum sustained winds of 157 mph or higher,” Feltgen said.
Irma’s peak speed was recorded at more than 180 mph, capable of rendering an affected area uninhabitable for weeks or longer, destroying buildings and wiping out utilities for months.
“The categories are just a guide,” said Alan Blumberg, a professor of ocean engineering at Stevens Institute of Technology in Hoboken, New Jersey.
And the NHC doesn’t take changes to the scale lightly. The only change made since the 1970s was in 2012, when scientists broadened Category 4 by 1 mph on each end to resolve an issue with converting to different units of measurement.
Asked if there was any chance of adding a new category, Feltgen said there was none.
There’s more to hurricanes than the scale
Blumberg argues that there’s little point in asking the public to recognize stronger storms. High wind brings up cold deep-ocean water, which weakens hurricanes or snuffs them out completely before they even reach land.
Wind speed is also just one piece of the larger hurricane tracking puzzle. It may be accessible, but Blumberg said it’s not always the most accurate predictor of strength or the extent of damage a major storm can cause.
For instance, storm surge and barometric pressure aren’t part of the scale, and as NHC notes, property destruction is relative, often depending on building codes and land topography.
Superstorm Sandy wasn’t a major storm by wind standards, but major in terms of storm surge, Blumberg said.
The source of the confusion
Some in the scientific community have debated in recent years whether to add another scale category, which is why the topic has come up in a number of blogs and scientific publications.
Climate change and rising ocean temperatures have stoked fears about future hurricanes increasing in frequency and severity.
Blumberg said hurricanes feed off warm waters and there is a correlation between water temperature and stronger, wetter storms.
But as The Associated Press reported, it’s not clear whether a particular storm can be attributed to man-made climate change without extensive study.
The bottom line is that specifics are important. Blumberg said “catastrophic” language around the categories and storms often causes people to panic, even if it’s not founded.
“Don’t panic, just be smart,” Blumberg said.
Category 1: Winds 74-95 mph. Very dangerous winds could damage wood frame houses. Extensive damage to power lines and poles. Likely power loss up to several days.
Category 2: Winds 96-110 mph. Extremely dangerous winds cause extensive damage to frame houses. Many trees snapped, blocking roads. Near-total power loss for days to weeks.
Category 3: Winds 111-129 mph. Devastating damage. Major damage to homes, uprooted trees, blocked roads. Near-total power and water loss for days to weeks.
Category 4: Winds 130-156 mph. Catastrophic damage. Severe damage to homes, most trees snapped or uprooted. Some areas isolated. Power outages for weeks or months. Most of the area uninhabitable for weeks or months.
Category 5: Winds 157 mph and higher. Catastrophic damage. High percentage of framed homes destroyed, with total roof failure and wall collapse. Some areas isolated. Power outages for weeks or months. Most of the area uninhabitable for weeks or months.
Source: National Hurricane Center