Scientists propose adding a "Category 6" to the current hurricane intensity scale

For over five decades, the National Hurricane Center has relied on the Saffir-Simpson Wind Scale to categorize hurricanes, ranking them from Category 1, with wind speeds of 74 to 95 mph, to Category 5, which includes winds of 158 mph or greater.

However, as ocean temperatures rise and hurricanes grow more intense and destructive, scientists Michael Wehner of Lawrence Berkeley National Laboratory and James Kossin of the First Street Foundation are questioning whether the current scale adequately communicates the risk of hurricane damage in today’s changing climate.

The case for a Category 6 hurricane classification

In their research, Wehner and Kossin introduce the concept of a Category 6 for hurricanes, which would cover storms with winds exceeding 192 mph.

Their work stems from a need to address how the existing scale’s open-ended Category 5 might lead to an underestimation of risk, especially in a warming world.

“Our motivation is to reconsider how the open-endedness of the Saffir-Simpson Scale can lead to underestimation of risk, and, in particular, how this underestimation becomes increasingly problematic in a warming world,” Wehner explains.

The duo’s analysis of hurricane data from 1980 to 2021 revealed five storms that would qualify as Category 6, all occurring in the last nine years of the record.

Global warming and the future of hurricanes

This finding, alongside the recognition that hurricanes, typhoons, and tropical cyclones are geographically named manifestations of the same weather phenomenon, underscores the escalating threat posed by these storms.

Their research not only revisits historical data but also employs simulations to forecast how a warming climate might affect hurricane intensity.

Results indicate that a 2°C rise in global temperatures could increase the risk of Category 6 storms by up to 50% near the Philippines and double it in the Gulf of Mexico, with Southeast Asia, the Philippines, and the Gulf of Mexico facing the highest risk.

Wehner emphasizes the significance of these findings in the context of the Paris Agreement’s goals to cap global warming at 1.5°C above pre-industrial levels.

“Even under the relatively low global warming targets of the Paris Agreement, the increased chances of Category 6 storms are substantial in these simulations,” he points out.

Comprehensive impact of hurricanes

The scientists argue that expanding the Saffir-Simpson Scale to include a sixth category won’t directly address the broader impacts of hurricanes, such as inland flooding and storm surge.

However, it could play a crucial role in raising public awareness about the heightened risk of major hurricanes in a warming climate.

Kossin adds, “Tropical cyclone risk messaging is a very active topic, and changes in messaging are necessary to better inform the public…Our results are not meant to propose changes to this scale, but rather to raise awareness that the wind-hazard risk from storms presently designated as Category 5 has increased and will continue to increase under climate change.”

This study serves as a call to action for updating hurricane risk communication methods to better reflect the realities of climate change, ensuring that the public is adequately informed about the evolving nature of storm threats.

Understanding the Saffir-Simpson Hurricane Wind Scale

As discussed above, the Saffir-Simpson Hurricane Wind Scale stands as a crucial tool for meteorologists, emergency responders, and the public to understand and assess the intensity of hurricanes.

Developed in the early 1970s by civil engineer Herbert Saffir and meteorologist Robert Simpson, then director of the U.S. National Hurricane Center, this scale categorizes hurricanes into five distinct categories based on their sustained wind speeds.

Each category reflects the potential for damage and flooding that a hurricane can cause upon making landfall.

How the hurricane category scale works

The scale assigns hurricanes a category from 1 to 5. Category 1 hurricanes have the lowest wind speeds (74-95 mph), while Category 5 hurricanes feature the highest (greater than 157 mph).

As the category number increases, so does the potential for significant damage to buildings, infrastructure, and the natural environment.

Category 1 hurricane: Minimal damage

Category 1 hurricanes can cause some damage to unanchored mobile homes, vegetation, and poorly constructed signs.

However, well-constructed frame homes can generally withstand the wind forces, experiencing primarily damage to shingles, vinyl siding, and gutters.

Category 2 hurricane: Moderate damage

With winds from 96 to 110 mph, Category 2 storms can cause extensive damage to roofs, windows, and doors of buildings.

Mobile homes, poorly constructed signs, and piers may face considerable damage or destruction. Near-coastal flooding and some injuries to people and animals due to flying and falling debris are more common in this category.

Category 3 hurricane: Extensive damage

Category 3 hurricanes, with wind speeds ranging from 111 to 129 mph, can cause devastating damage.

Well-built framed homes may incur major damage or removal of roof decking and gable ends. Electricity and water are likely to be unavailable for several days to weeks after the storm passes.

Category 4 hurricane: Extreme damage

Winds of 130 to 156 mph characterize Category 4 hurricanes.

These storms can cause catastrophic damage, with most trees snapped or uprooted, power poles downed, and residential areas isolated due to fallen trees and power poles. Most of the area will be uninhabitable for weeks or months.

Category 5 hurricane: Catastrophic damage

The highest category, Category 5, represents hurricanes with wind speeds of 157 mph or higher.

These storms can level houses, destroy industrial buildings, and cause widespread power outages that could last for weeks or months. Most of the area will be uninhabitable for the same duration.

Critical tool for preparedness

The Saffir-Simpson Hurricane Wind Scale serves as a fundamental component of hurricane preparedness and response strategies.

It helps to communicate the potential impact of hurricanes in a clear and understandable way, enabling individuals, communities, and governments to take appropriate actions to safeguard lives and property.

By providing a standardized measure of storm intensity, the scale plays a vital role in the planning and execution of evacuation orders, the allocation of resources, and the overall management of disaster response efforts.

In summary, the Saffir-Simpson Scale is a vital tool that helps predict the potential damage from hurricanes, guiding preparation and response efforts to minimize the impact of these powerful storms on our communities.

The study was published in the journal Proceedings of the National Academy of Sciences.

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