Hurricanes have long been a potent symbol — maybe the most potent — of a changing climate. Not only do these storms release destructive energy on a scale that’s staggering to contemplate, but how much they can do so depends on the heat contained in ocean water — their power source.
That’s what makes it so striking to find Jeff Masters, a hurricane expert and co-founder of the Weather Underground, declaring that late October’s Category 5 Hurricane Patricia wasn’t just the strongest hurricane ever seen in the Western hemisphere. No, Masters asserts that Patricia was the strongest tropical cyclone ever reliably recorded by humans, at least when measured by its wind speeds. (Tropical cyclones go by various names, including hurricanes and typhoons, in different parts of the world).
“I regard Patricia as unmatched for the strongest winds of any tropical cyclone in recorded history,” Masters wrote on Monday. He later continued: “Now that ocean temperatures are considerably warmer than they were a few decades ago, the maximum potential intensity a hurricane can reach is higher, and we should expect to see a few Patricias sprinkled among the inevitable phalanxes of major hurricanes that will assault our shores in the coming decades.”
We’d already known, of course, that Patricia was a remarkable hurricane. On Oct. 23 of last year, when the storm reached its peak intensity, the National Hurricane Center (NHC) judged Patricia to have achieved maximum sustained wind speeds of 175 knots (201 miles per hour) and a minimum central pressure of 880 millibars. (Hurricane wind speeds and pressures are closely related because winds spiral inward toward regions of low pressure and, in general, do so faster the lower the pressure gets).
“This makes Patricia the strongest hurricane on record in the National Hurricane Center’s area of responsibility (AOR) which includes the Atlantic and the eastern North Pacific basins,” wrote the agency’s forecaster Richard Pasch. And this is why, in immediate press coverage of the storm, Patricia was often referred to as the strongest hurricane on record in the Western hemisphere.
However, post-hurricane season, the National Hurricane Center did a more thorough analysis of Patricia, which is what prompted Masters’ post. Looking at all the evidence, the agency bumped up the storm’s maximum sustained winds to 185 knots (about 213 miles per hour) and lowered the minimum central pressure to 872 millibars. Yet the NHC didn’t go quite as far as Masters and say that Patricia was the strongest tropical cyclone, for wind speeds, ever recorded, simply reiterating that Patricia had been the strongest hurricane in the National Hurricane Center’s area of responsibility. (One Pacific supertyphoon, Tip of 1979, had a minimum central pressure measured at 870 millibars).
So is Masters really right? To find out, I canvassed several hurricane experts — none of whom disagreed outright with his analysis, though they did note some key caveats.
In determining whether Patricia was really the globe’s strongest tropical cyclone on record (for wind speeds), there are several key issues that have to be addressed. The first is the simple fact that, as Masters noted, when you pore over our hurricane records, it turns out that the 1961 Pacific typhoon Nancy was also recorded as having 185 knot winds.
However, Masters discounted this measurement, writing that “the maximum sustained winds estimated in typhoons like Nancy during the 1940s to 1960s are considered by hurricane experts to be too strong; a re-analysis of Super Typhoon Nancy would likely find that its winds were considerably slower than 215 mph.” A World Meteorological Organization list of tropical cyclone records also names Nancy as the storm with the strongest wind speeds, but similarly notes that “It is now recognized that the maximum sustained winds estimated for typhoons during the 1940s to 1960s were too strong.” The group says it is currently analyzing Patricia.
The second issue is that scientists don’t measure storms in the same way in every basin of the globe — observing technologies differ, and many storms go unmeasured by aircraft in the way that Patricia was. Instead, they’re only measured based on satellite imagery. This means that in one of the other hurricane basins outside of U.S. responsibility — the northwest Pacific, the north or south Indian Ocean, the south Pacific, and so on — there could well have been a stronger storm than Patricia, but scientists never knew it. This is a tougher and ultimately, perhaps, impossible issue to resolve.
It’s also true that the farther back in time you go, as observational technologies become poorer and poorer, the uncertainty about whether there was a storm stronger than Patricia grows. However, concerns like this are precisely why Masters is saying it’s the strongest tropical cyclone “in recorded history” for its wind speed, not the strongest storm ever. Masters himself acknowledges this, writing, “It is possible that previous hurricanes where hurricane hunter flights were not available, such as the Category 5 1935 Labor Day hurricane that devastated the Florida Keys, had peak winds on par with Patricia, though.”
So what do other experts think?
“I agree with Jeff’s analysis,” said James Elsner, a hurricane researcher at Florida State University, by email. He added, “With warmer oceans the chance of extreme hurricanes like Patricia increase. There is plenty of evidence that the strongest hurricanes are getting even stronger.” Elsner recently co-authored a study in the Journal of Climate finding that in the western North Pacific in particular — typhoon territory — “tropical cyclone formation is becoming less common, but those that do form are likely to reach extreme intensities from the discharge of stored energy.”
“To me the revision by NHC seem reasonable, given the aircraft observations, and the additional information such as record warm temperatures at 700 mb (the warmer the air aloft the lower the surface pressure),” added Greg Holland, a hurricane researcher at the National Center for Atmospheric Research. “This would indeed make it up there in the top couple of most intense storms in the world.”
“The one caveat is that the rest of the world uses satellite interpretation, which would make it very difficult for assessing really extreme events — as it would be subject to valid criticism,” continued Holland, who has also published research suggesting that a greater proportion of all hurricanes are now reaching category 4 or 5 strength.
I also reached Jim Kossin, a hurricane researcher with NOAA’s National Centers for Environmental Information. He observed that “Patricia is undoubtedly at the extreme end of the spectrum of intense tropical cyclones, and is an excellent example of the kind of tropical cyclone that theory and models suggest will become more probable under anthropogenic climate change. The rest comes down a bit to splitting hairs and how much uncertainty one is willing to allow.”
When it comes to whether 1961’s Typhoon Nancy was over-measured, Kossin agrees with Masters. “It’s more likely than not that Nancy was overestimated, which would put Patricia ahead,” he said. But when it comes to the question of whether some other storm could have been recorded as stronger if there had been better technology to sample its winds, he answered, “Absolutely. There is a range of uncertainty that we have to deal with that makes these hard-line questions about lowest pressure or highest winds ever recorded a bit overly ambitious.”
So what can you conclude from all of this? Acknowledging the limited information we have to go on, Masters’ approach is hardly unreasonable. Nancy was probably over-measured, and if so, that would leave only Patricia with sustained winds measured at 185 knots.
The outstanding issue remains what we don’t know and can’t know, and how much emphasis you put on that. Nonetheless, at the end of the day, and caveats acknowledged, Patricia is enough to make anyone worry about what’s happening to the planet’s oceans and atmosphere.
More at Energy & Environment: