Stronger hurricanes require new Category 6, researchers say

Mega-hurricanes: Huge spiral storm of thick white clouds seen from above, with brown land and blue ocean seen below it.
View larger/full image. | Hurricane Patricia of 2015 was the most powerful tropical cyclone on record worldwide in terms of wind speed and the 2nd-most intense storm on record worldwide in terms of pressure. Here it is near Mexico on October 23, 2015. Patricia had wind speeds of up to 215 mph (346 kph), much higher than the required sustained wind speeds for Category 5 hurricanes. Do we need a Category 6? Image via NASA Earth Observatory.
  • Earth is witnessing a rise in the intensity of hurricanes, attributed to the warming of both the air and oceans.
  • Researchers propose for a new hurricane category, Category 6, to accommodate the observed increase in hurricane strength.
  • They suggest classifying hurricanes with sustained wind speeds of 192 mph (309 kph) or more under this new category. The current highest category of hurricanes begins at sustained wind speeds of 157 mph (253 kph).

Hurricanes are getting stronger. That’s because the warmth of the air and the oceans drives hurricanes, and both Earth’s air and Earth’s oceans are getting warmer. So we’re already seeing mega-hurricanes like Hurricane Patricia of 2015, the most powerful tropical storm on record worldwide, in terms of wind speed. And now some researchers are now calling for a new category to be added to the currently used hurricane scale. Currently, that scale ranks hurricanes from 1 to 5. Michael Wehner of the Lawrence Berkeley National Laboratory in California and James Kossin of the University of Wisconsin-Madison proposed on February 5, 2024, that we add a new Category 6 for hurricanes.

Hurricanes must have sustained wind speeds greater than 157 mph (253 kph) to be ranked as Category 5. Wehner and Kossin propose sustained winds of 192 mph (309 kph) or more for Category 6 hurricanes.

The researchers published their peer-reviewed findings in the Proceedings of the National Academy of Sciences on the same day.

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Intensity of hurricanes increasing

As the oceans and atmosphere continue to warm, mega-hurricanes are becoming stronger. While the number of hurricanes is remaining about the same, the strength of them is increasing. Indeed, as Milan noted in The Guardian, the intensity of hurricanes has notably increased during the four-decade period of satellite records.

More often now, hurricanes are reaching the level of unprecedented sustained winds, pushing the limits of Category 5 (157 mph/253 kph or more). Wehner and Kossin say that such atypical strong hurricanes – with winds of 192 mph (309 kph) or more – should be re-categorized as Category 6 on the Saffir-Simpson Hurricane Wind Scale. Oliver Milman wrote about the proposed change for The Guardian on February 5, 2024. Wehner told him:

[A sustained wind speed of] 192 mph is probably faster than most Ferraris. It’s hard to even imagine. Being caught in that sort of hurricane would be bad. Very bad.

The paper stated:

Global warming leads to more intense tropical cyclones (TCs). Three separate lines of evidence from both observations and models suggest that the open endedness of the 5th category of the Saffir–Simpson hurricane wind scale becomes increasingly problematic for conveying wind risk in a warming world. We investigate considering the extension to a 6th category of the Saffir–Simpson hurricane wind scale to communicate that climate change has caused the winds of the most intense TCs to become significantly higher.

Chart with green to red sections for categories 1 to 5, with text descriptions.
This is the current Saffir-Simpson Hurricane Wind Scale. The highest level is Category 5, with sustained winds of 157 mph or higher. Image via NASA.

Only a matter of time until more extreme hurricanes in Atlantic Ocean

Category 5 hurricanes are bad enough. Hurricane Katrina in 2005 and Hurricane Maria in 2017 are two examples of how powerful they can be. But hurricane winds reaching 192 mph or more is a new extreme. So far, that has been mostly limited to storms in the Pacific Ocean, for example, Typhoon Haiyan in the Philippines in 2013, which killed over 6,000 people and Hurricane Patricia near Mexico in 2015. In fact, Maria’s winds reached a top speed of an incredible 215 mph.

But overall, such mega-hurricanes are already starting to become more frequent. When the research team performed a historical data analysis of hurricanes from 1980 to 2021, they found five that would have been classified as Category 6, if it existed on the scale now. All of them occurred within a nine-year period.

It may only be a matter of time until hurricanes in the Atlantic Ocean reach the same levels. As Wehner noted in The Guardian:

There haven’t been any in the Atlantic or the Gulf of Mexico yet but they have conditions conducive to a Category 6, it’s just luck that there hasn’t been one yet. I hope it won’t happen, but it’s just a roll of the dice. We know that these storms have already gotten more intense, and will continue to do so.

He also said:

Even under the relatively low global warming targets of the Paris Agreement, which seeks to limit global warming to just 1.5 degrees Celsius above preindustrial temperatures by the end of this century, the increased chances of Category 6 storms are substantial in these simulations.

Greater awareness of climate change

The researchers said that having a new Category 6 would help to make people more aware of how climate change is affecting hurricanes and other storms. Wehner said:

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.

He also noted in The Guardian:

Our main purpose is to raise awareness that climate change is affecting the most intense storms.

They also noted how the Saffir-Simpson hurricane scale has been good for measuring severe rainfall and coastal flooding, but needs improvement regarding actual wind speeds. The researchers don’t want to change the scale itself as such, but rather to adapt it to a changing climate. Kossin said:

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.

Other climate change-related modifications

If ever enacted, this wouldn’t be the first climate change-related modification made. In Australia, the Bureau of Meteorology added the color purple to its weather maps. This is to indicate areas and incidents of intense heat, another factor becoming more common. In late January, the Coral Reef Watch program in the U.S. added three new alert categories. The additional categories measure the increasing heat stress being experienced by coral reefs.

Bottom line: Hurricanes are becoming stronger due to climate change. And 2 researchers in the U.S. say we need a new Category 6 to classify mega-hurricanes.

Source: The growing inadequacy of an open-ended Saffir–Simpson hurricane wind scale in a warming world

Via Lawrence Berkeley National Laboratory

Via The Guardian

Read more: Global warming is making hurricanes stronger

Read more: Hurricanes heat the ocean, even far from the storm

February 12, 2024

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