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| Satellite image of Category 5 Hurricane Melissa last month. It was such a powerful storm that it is once again raising the question of whether there should be a new Category 6 for extra powerful hurricanes. |
Melissa was part of a spate of Atlantic hurricanes that were much more powerful than most past storms.
Climate change might be making some hurricanes stronger than ever before, even though the overall number of such storms doesn't seem to be increasing.
Hurricane strength is determined by the Saffir-Simpson Hurricane Scale. It's a five-point scale, with the worst hurricanes being Category 5, with winds of 157 mph or more.
On that scale, the difference in wind speed between the categories of hurricanes is around 30 mph, give or take. For instance, a top range Category 4 hurricane has winds 27 mph stronger than a top-tiered Category 2 hurricane.
The peak winds in Category 5 Hurricane Melissa were 185 mph, or 28 mph above the threshold for that category.
With hurricanes likely getting stronger and stronger amid climate change, will hurricanes need a Category 6? And how would that work?
Meteorologists and other scientists are beginning to grapple with the question.
"It's been proposed that such a hurricane would have maximum sustained winds of 192 miles per hour and could do much more damage than structures designed to withstand Category 5 winds are able to handle."
Hurricane Melissa came close to this theoretical Category 6, falling just 7 mph under that proposed category. Post-storm analysis might boost Melissa's top winds to or over 192 mph, because there is some uncertain, preliminary evidence that winds might have been higher than first reported.
Meteorologists are divided on the issue.
Certainly, some support the idea of creating a Category 6.
"As long as we're using wind-based metrics, it simply doesn't make sense (mathematically or fiscally or sociologically) to artificially cap the scale at 5 any more," said Climatologist Michael Mann.
Katharine Heyhoe, an atmospheric scientist and Chief Scientist at the Nature Conservancy, told the Independent that a Category 6 would take into account the worrisome effects of climate change and the bigger risk of damage from worsening storms.
Heyhoe said the whole Saffir-Simpson scale might need a full redesign to take into account rainfall amounts associated with hurricanes. Flooding is responsible for a majority of the hurricane-related economic impacts.
On the other hand, Phil Klotzbach, an atmospheric scientist and hurricane expert at Colorado State University, said a Category 6 is unnecessary. Category 5 storms can leave communities uninhabitable for weeks or months, so the effects of a supposed Category 6 would have little practical difference.
Another problem with fudging with the Saffir-Simpson scale is it would make it hard to compare storms decades ago with ones that occur under a scoring system with a Category 6.
"If we change it, it becomes difficult to compare new storms to old ones unless we reanalyze past data. We'd be moving the goalposts for what defines a 'major' hurricane," said Dr. Zachary Handlos, director of Atmospheric and Oceanic Sciences Undergraduate Degree Program at Georgia Tech, in an interview with WCNC.
However, Handlos said it could still be worth it to establish a new classification system for hurricanes. The Saffir-Simpson scale only takes into account wind speeds.
Which means the scale doesn't capture a hurricane's a storm's full impact. Hurricanes cause severe inland flooding storm surges and tornadoes, all of which can devastate towns and cities far from where the hurricane came ashore.
Hurricane Helene last year is a classic example of that. It came ashore in Florida but destroyed swaths of western North Carolina.
Storm surges and rainfall cause almost 80 percent of hurricane deaths, which is a good reason to revamp the hurricane categorizing system.
Handlos said a new hurricane rating system should be easy enough for the public to understand. They need to know right away whether they should evacuate, whether they're allowed to drive through the immediate aftermath of a hurricane, how big the flooding threat is, that type of thing.
There already is an alternative hurricane rating system.
As Live Science reports, Jennifer Collins, a professor in the School in Geosciences at the University, and her colleagues developed the hurricane rating system called TCSS taking into account wind speed, storm surge and rainfall.
Collins' hurricane rating system scores between one and five each of the three hazards, depending on their predicted severity for a given hurricane. The scores are combined into a final score.
Collins' research team sent 4,000 participants living along the Gulf and East coasts forecasts for 10 fictitious hurricanes affecting their communities.
Half the participants received warnings based on the Saffir-Simpson scale, while the other half got her TCSS system. The participants then filled out an online quiz about how they would react under the different scenarios.
It turns out people who received the TCSS forecasts were more likely to identify the main hazard from a hurricane correctly, and significantly more likely to evacuate for non-wind hazards than if they had received the Saffir-Simpson rating.
The survey participants also were more likely to take the correct precautions, such as setting out sandbags, or put up window protections with Collins' warning system.
As we noted, hurricanes are not just about wind. Some hurricanes have relatively weak winds, but incredible amounts of rain. (Think Hurricane Irene, which affected Vermont in 2011).
The trick is to make a warning system that acknowledges the complexity of the storm, but at the same time keeps things simple so that the public knows how to react to the hurricane.
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