What’s The Strongest Hurricane Ever – And What’s The Strongest Possible?

As you’re probably aware by now – particularly if you live anywhere in the vicinity of Tampa Bay – it’s hurricane season in the tropical Atlantic.

And what a season it’s been so far. There have been no fewer than five hurricanes in less than two weeks – not an unusual total for the entire year typically – and they’ve included both Helene, the deadliest Atlantic hurricane to hit the mainland US since Katrina, and Milton, the strongest tropical cyclone in the world so far this year.

So, as Floridians scramble to make sense of the devastation across their state, it’s worth asking: could the next one be even worse?

How are hurricanes measured?

Before we can say what the most powerful hurricane is, was, or could potentially be, we probably ought to look at what “most powerful” actually means.

In general, there are two main ways to measure a hurricane’s intensity: either by measuring the storm’s barometric pressure – the lower the pressure, the stronger the storm – or using the Saffir-Simpson Hurricane Wind Scale (SSHWS). You’re probably fairly familiar with this latter metric: you might have heard about Hurricane Milton, for example, growing from a “Category 1” to a “Category 5” hurricane in just 12 hours, and how that was making a lot of meteorologists very nervous. But what does it actually mean?

The Saffir-Simpson Scale – a scale that runs from one to five, with five being the most powerful type of hurricane – was developed back in the late 1960s and early 1970s by Herbert Saffir, a consulting engineer who lived in Florida, and Robert Simpson, then the director of the National Hurricane Center.

“Saffir began working on the scale in 1969 after his work on a United Nations commission, which had been looking at preventing damage to low-cost housing in Hurricane Alley, turned up no options for quantifying hurricane damage,” explained Weather Channel meteorologist Jonathan Belles in 2020. “The first version of the scale showed up in 1972.”

Although the scale did, for a long time, attempt to take into account details like storm surge and flooding, since 2009 it’s been based purely on maximum sustained wind speed. That might sound like a step backward, but there were good reasons for doing so: “storm surge values and associated flooding are dependent on a combination of the storm’s intensity, size, motion and barometric pressure, as well as the depth of the near-shore waters and local topographical features,” explained a National Oceanic and Atmospheric Administration (NOAA) press release at the time. “As a result, storm surge values can be significantly outside the ranges suggested in the original scale.”

Today, the scale runs like this: a category 1 hurricane has winds that reach 119–153 kilometers per hour (74–95 miles per hour); category 2 ranges from 154–177 kmph (96–110 mph); category 3 gets to 178–208 kmph (111–129 mph); category 4 hurricanes have wind speeds of 209–251 kmph (130–156 mph); category 5, the highest category, is anything above 252 kmph (157 mph).

They’re a helpful guide for the public, but the system is not without its critics. While they’re commonly linked to vague predictions of damage levels – as a general rule, “damage rises by about a factor of four with every category increase,” advised Belles – experts are keen to point out that the categories can’t be relied on totally to guide how to react to storms. After all, Hurricane Katrina was only a category 3 when it made landfall over Louisiana back in 2005, and the state is still struggling to completely recover from her effects today.

“When the National Hurricane Center says Category 1, the attitude by the public is that it’s fine and they can live through it,” said Vasu Misra, a professor of meteorology at Florida State University, in 2014. “But, the damage by flooding is typically more widespread in larger storms.”

The strongest hurricane ever recorded

So now we know how tropical cyclones are categorized, which one – or should we say “who”? – comes out on top?

Well, let’s first look at the storms with the lowest barometric pressure – and by this metric, the winner is one you might not be too familiar with. Typhoon Tip, the third super typhoon of the 1979 Pacific typhoon season and to this day the largest tropical cyclone on record, raged across the Western Pacific for 20 straight days in October of that year, and to give you an idea of how big it was, here’s an image of it compared to the contiguous US. 

It hit its lowest pressure on October 12 – a record 870 hectopascals (hPa) (12.6 psi). That’s about one-seventh less than normal atmospheric pressure at sea level – to put it another (probably less helpful) way, basically the same as the air pressure at the top of one and a half Burj Khalifas (told you).

As you might expect, such a huge and intense storm caused one hell of a lot of damage – mostly in or around Japan, which it hit, incredibly, after it had already passed its peak strength.

“The typhoon was […] the most intense to hit Japan’s main island of Honshu in more than a decade,” recalled a 2012 AccuWeather article. “Tip claimed the lives of 86 people and injured hundreds of others.” 

“The extreme winds of Tip knocked over a gasoline storage tank, causing an explosion and fire that spread rapidly through a U.S. Marine Corps camp at Mt. Fuji,” it continued. “Extensive flooding destroyed more than 20,000 homes in Japan, while hundreds of mudslides occurred […] High-rise buildings in Tokyo swayed from the high winds as the typhoon struck.”

Now, Tip also clocked some pretty insane wind speeds – the highest sustained for a minute, which is how the SSHWS measures them, maxed out at 305 kmph (190 mph). But amazingly, that’s not the fastest wind speed on record. Not by a long shot.

“On Oct. 23, 2015, [Hurricane] Patricia was spinning off the coast of Mexico in the eastern Pacific Ocean,” Belles recalled in a 2018 article for the Weather Channel. The storm “smashed records for intensity in the Western Hemisphere before raking into southwest Mexico,” with “maximum sustained winds [that] topped out at an incredible 215 mph [346 kmph].”

For an idea of how that might feel, imagine being taped to the front of a bullet train at top speed – then add a little extra. It’s a full 40 kmph faster than the runner-up – Hurricane Allen, from 1980, which even today is commonly used as a benchmark for just how bad things can get in a really devastating storm.

Now, on the face of it, that may sound surprising – after all, if Patricia was worse, why do we still remember Allen as the standard bearer? Well, here’s the thing: Allen, while certainly no Katrina, was pretty destructive, claiming at least 269 lives and causing around $6 billion worth of damage in today’s money. 

Patricia, on the other hand, “didn’t end up causing anywhere near as much devastation as feared,” Vox reported at the time. “The hurricane hit Mexico’s coast at around 7 pm on Friday, a Category 5 storm with winds reaching upward of 165 mph [266 kmph]. Within a day, the storm had weakened considerably, chewed up by mountainous terrain. So far, six deaths have been reported – far fewer than that from many other major hurricanes – and much of Mexico’s major infrastructure has survived intact.”

So, how did we escape so (relatively) unharmed from the strongest hurricane on record? Partly through good luck, and partly through preparedness. Patricia happened to pass through relatively unpopulated areas, and also happened to be quite compact – but also, local authorities in Mexico had an effective emergency response program in place, with shelters and evacuation programs set up before the storm hit, and clean-up crews deployed soon after.

The moral of the story: prevention really is better than cure.

The strongest hurricane possible

So, is that it, then? So few hurricanes reach anywhere close to Patricia’s speeds or Tip’s pressures – perhaps that’s simply as strong as they can ever get?

Well, in a sense, that’s true. There is, kind of, a limit on how fast sustained wind speeds can become – but it isn’t fixed. It depends on a number of factors – primarily the ratio between the temperature of the ocean and the cloud tops, but also things like wind shear or atmospheric heat.

Nevertheless, the limit usually comes out somewhere around 320 kmph (200 mph)… for now. But “I think by the end of the century, if we don’t do a lot of curbing, it’s going to be closer to 220 [mph / 354 kmph],” Kerry Emanuel, an emeritus professor of atmospheric science at MIT who developed the model for estimating the maximum, told Live Science this month.

That’s right: it’s our old friend climate change, here to ruin everyone’s day again. Hurricanes today are significantly more intense than they used to be; they intensify faster than they used to, and hurricane season itself lasts longer than it once did.

“The fuel for the hurricanes is the heat they’re drawing from the ocean,” James Kossin, a climate and atmospheric scientist retired from the NOAA, told Live Science. “The warmer the water, the more fuel is available.”

In fact, things are looking so bleak that some experts are toying with the idea of extending the SSHWS itself – making way for a future in which category 6 or even 7 storms might be a reality.

It’s a controversial idea, for many reasons. “We don’t want to overemphasize the wind hazard by placing too much emphasis on the category,” Jamie Rhome, deputy director for NOAA’s National Hurricane Center, told the BBC earlier this year – and, since Category 5 already describes “catastrophic damage”, it’s “not clear that there would be a need for another category even if storms were to get stronger,” he said.

Others worry that adding a Category 6 might dilute the severity of the preceding categories in the public’s mind. “One of my concerns would be: is that going to make somebody think even less of a category one or category two, which are still significant threats?” Heather Holbach, a research assistant with the hurricane research division at NOAA, said. “I think there’s a huge social science component that needs to be understood a lot more.”

On the other hand, extending the category system to include stronger, more intense storms may be a necessary wake-up call.

“I’m in favor of ditching the Saffir-Simpson scale and starting afresh,” Emanuel told the BBC. But if we are going to keep it, he said, adding a category 6 could send a “clear message to people that climate change is influencing hurricanes.”

“Its primary utility would be to draw attention to that fact.”

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