Has the Era of Category 6 Hurricanes Arrived?

Hurricane Florence churning over the Atlantic, as captured by astronauts on the International Space Station. (Photo: NASA)

In October 2015, the most powerful hurricane ever recorded in the Western Hemisphere churned its way along the Pacific coast of Mexico. Named Patricia, the massive storm awed the world of meteorology as it intensified in only 24 hours from 85 mph sustained winds to 205 mph. At its peak on Oct. 23, the storm reached top sustained winds of 215 mph.

Fortunately, Hurricane Patricia made landfall in a rural part of Mexico's West Coast. While eight people lost their lives, meteorologists say we were lucky the storm didn't strike closer to a major population center.

"It would have been devastating," Kristen Corbosiero, a professor in the Department of Atmospheric and Environmental Sciences at the University of Albany, told NPR. "I think it's really hard to think about what it would have been like, that if a storm like this had intensified so rapidly, say, near the coast of Florida or near the coast of Texas or even further up or down the coast in Mexico — we were very lucky that the storm didn't make landfall in a more populated area."

According to a computer simulation created at the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, explosively intensifying hurricanes may become more common in the future. Even Hurricane Florence, shown below in a video captured aboard the International Space Station, jumped from 75 mph to 130 mph is a little over 24 hours.

In a paper published in the journal American Meteorological Society, the researchers explain how they fed the simulation different values for ocean and atmospheric forces, starting with a control group of recorded observations from 1986 to 2005, and then "nudging" the numbers based on middle-of-the-road future climate change estimates. While the model predicted more hurricanes in general, it found a general increase of 20 percent more of the worst storms.

"What's more, the research found that storms of super-extreme intensity, with maximum sustained winds above 190 mph, also became more common," writes Chris Mooney of the Washington Post. "While it only found nine of these storms in a simulation of the late 20th century climate, it found 32 for the period from 2016 to 2035 and 72 for the period from 2081 to 2100."

The case for Category 6

With many more future storms expected to occupy wind speed territories like those of Hurricane Patricia, scientists are seriously giving thought to expanding the Saffir-Simpson hurricane scale to include a "Category 6" designation. Introduced to the public in 1973, the scale has an open-ended category system that currently ranks "Category 5" storms at anything with sustained winds of 157 mph or greater.

The Saffir–Simpson hurricane wind scale.
The Saffir–Simpson hurricane wind scale. (Photo: Wikipedia)

The Saffir–Simpson hurricane wind scale. (Image: Wikipedia)

At first glance, making room for Category 6 storms on the Saffir-Simpson scale appears to make sense. After all, less than 30 mph divides the other categories. Hurricane Patricia was a stunning 58 mph over the minimum for a Category 5. With even more hurricanes like it expected in the 21st century, researchers say the ominous designation could help people better understand the stark implications of climate change.

"Scientifically, [six] would be a better description of the strength of 200 mph storms, and it would also better communicate the well-established finding now that climate change is making the strongest storms even stronger," climatologist Michael Mann argued during a meteorological conference in New Zealand earlier this year. "Since the scale is now used as much in a scientific context as it is a damage assessment context, it makes sense to introduce a category six to describe the unprecedented strength 200 mph storms we've seen over the past few years both globally [Patricia] and here in the Southern Hemisphere [Winston]."

Rather than add a new category, others have suggested reworking the current scale to better reflect the intensifying nature of hurricanes. So instead of a Category 4 reflecting wind speeds of 130-156 mph, it might cover a wider value up to 170 mph. Either way, should monster storms muscle their way into the annual hurricane cycle, researchers agree the present scale will likely have to be amended.

"If we had twice as many Category 5s — at some point, several decades down the line — if that seems to be the new norm, then yes, we'd want to have more partitioning at the upper part of the scale," Timothy Hall, senior scientist at the NASA Goddard Institute for Space Studies, told the Los Angeles Times. "At that point, a Category 6 would be a reasonable thing to do."