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Hurricane Willa’s dangerous intensification, explained

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‘It’s unusual in that it intensified that quickly.’

Hurricane Willa nears Mexico on October 22nd 2018
Hurricane Willa nears Mexico on October 22nd 2018
Image by Joshua Stevens/NASA Earth Observatory

After a massive intensification over the weekend, Hurricane Willa is whirling toward Mexico’s west coast as a Category 4 storm. Everything about the storm will be life-threatening, the National Hurricane Center warns: hurricane-force winds, flash flooding, landslides, and storm surge are predicted along the storm’s path. “Preparations to protect life and property should be rushed to completion,” the National Hurricane Center says.

Just days ago, Hurricane Willa was a tropical storm, CNN reports. By Monday morning, Willa had become a Category 5 hurricane with winds reaching speeds of 165 miles per hour. By Monday afternoon, the winds had slackened just a little to 150 miles per hour, and the National Hurricane Center downgraded the storm to a Category 4. The storm is on track to hit the Isla Marías archipelago on Tuesday morning before striking mainland west-central Mexico later in the day.

While the storm’s expected to continue losing strength, the National Hurricane Center predicts it probably won’t lose a significant amount of steam before it hits Mexico. “Unfortunately landfall is tomorrow, so it doesn’t have a ton of time to weaken,” says Phil Klotzbach, an atmospheric scientist at Colorado State University. The storm is still set to be a major hurricane when it strikes land. “It definitely looks like a pretty serious threat,” he says.

After back-to-back hurricanes pummeling the east coast of the US, a hurricane on the Pacific coast of North America may seem surprising. But in fact, the northeastern Pacific is actually more prone to hurricanes than the Atlantic, Klotzbach says. So far, three Category 5 storms have formed in the northeast Pacific this year, probably due to a combination of favorable atmospheric conditions, and warm ocean waters. And taking storm frequency, duration, and intensity into account, this is the region’s most active hurricane season on record, he says

The Verge spoke with Klotzbach about hurricanes in the Pacific, Willa’s speedy intensification, and why this year is so odd.

This interview has been edited for clarity and brevity.

Is Hurricane Willa unusual?

It’s unusual in that it intensified that quickly. The models were always really aggressive at developing this storm. The [National] Hurricane Center has been watching this thing for a while, and it wasn’t really doing much — and then basically the bottom fell out of it and it went from a tropical depression to a Category 5 in like 48 hours, which is very impressive. Not the fastest, but definitely up there in terms of intensifying quickly.

In terms of its track, that’s pretty typical for late season storms in the east Pacific. They tend to move west and then go north and hook back into Mexico. So for the western coast of Mexico, getting stuff in October into November isn’t that uncommon. I think it’s probably going to weaken. But even if it’s a four or a three it’s certainly one of a stronger storms that have hit them.

Is there a pattern to hurricane formation in the Pacific, and does Hurricane Willa fit that pattern?

In the Pacific, the water temperatures get cold as you go further north — which is why we don’t see hurricanes hitting California — and also the shear gets quite strong. So storms in the northeast Pacific form in a nice tight little latitude-longitude area. And then most of them go west and track north, get to cold water, and die. Most hurricanes in the northeast Pacific don’t really impact people. Which is why frankly, in research, it’s probably the most neglected hurricane basin.

But then you do get these storms obviously, like we had Patricia [in 2015], which is probably the one that people remember the most. Hurricane Kenna in 2002 was a very strong hurricane that went into the western part of Mexico, and killed four people when it made landfall. Certainly you do get these kinds of storms that do these right-hook turns into Mexico, and Kenna is actually a pretty good analog in terms of its track because it made landfall as a [Category] 4 on October 25th — so about the same time. These kinds of powerful hurricanes have hit in the past in western Mexico, but obviously this one certainly has the potential to be quite strong when it hits.

We don’t hear about hurricanes in the Pacific as often as we hear about hurricanes in the Atlantic, is that because there are fewer?

There are actually more! This has been the most active northeast Pacific hurricane season on record, and no one pays attention to the storms because they generally go out to the middle of nowhere and die. So unless they go and hit Hawaii, like Lane did, people just kind of ignore them and go, “Oh, it’s a nice pretty hurricane out in the middle of nowhere doing no impacts to anyone.” But it’s been a phenomenally active northeast Pacific season. Climatologically the Atlantic has about 12 storms, and the northeast Pacific has 16, so they do get more. Not every year, but in general it’s more active than the Atlantic.

Why is that?

A lot of it is just that the shear is lower. Shear is basically the change in wind direction with height in the atmosphere. So the idea is that hurricanes want to be upright. If you have shear — if you have winds in one direction blowing, say, out of the east, and winds in the other direction blowing out of the west — that will basically tilt the hurricane circulation. It disrupts the vortex, and you just can’t get the deep thunderstorms you need to support the storm. So shear is detrimental for hurricanes, and when you get a lot of shear it tends to really knock down the season.

So you have an area of low shear right off the coast of Mexico, and the waters there are certainly plenty warm to support nasty hurricanes. One of the ideas is that a lot of the storms that form in the northeast Pacific actually come from disturbances moving off Africa. If they don’t develop in the Atlantic, sometimes they’ll [go all the way across the Caribbean and] develop in the eastern Pacific. So in a lot of ways, the Atlantic and the northeast Pacific tend to be inversely related: when the Atlantic is very active, the northeast Pacific tends to be quiet, and vice versa.

Is that what’s happening this year?

This year is kind of an oddball year. This year’s a little above normal in the Atlantic. But normally when the northeast Pacific is as active as it is this year, you wouldn’t expect the Atlantic to have much activity at all, so it’s a little unusual in that regard. That’s one of the many things we’re trying to figure out for this year: how those relationships that we have in our heads don’t always work.

Why did Willa intensify so quickly?

The waters are warm. I looked for Willa, they’re running about a degree warmer than normal. The interesting thing is that there’s some theoretical research that basically says when your water temperatures are at a certain level, the hurricane can only get so strong.

So Willa is right near as strong as a storm can get with the current water temperatures. Which basically means that the environment has to be pretty much perfect — because normally hurricanes are nowhere near as strong as they can possibly get for the water temperatures because of shear, and other factors that come into play and knock the storm down. The thing with Willa is that theoretically it really can’t get any stronger than it is, given the water temperatures that it’s under. And it looks like the shear is going to go up. So even though the water temperatures are going to get a little bit warmer, the shear is going to go up, and that should knock the storm down a little bit in intensity before it hits the coast.

What’s the role of climate change here in the active Pacific hurricane season, and with Willa?

In general, you have warmer waters, [which] provides more fuel for the storms. I would say that certainly, yes, it’s not going to help matters. But it’s not as simple and straightforward as saying you warm the surface of the ocean, you’re going to get stronger hurricanes. There’s other factors that come into play, too. When you warm the atmosphere in climate change, you warm throughout the atmosphere, not just the ocean surface, and that takes a little bit of the edge off of just warming the ocean’s surface.

This year we’ve had really low shear, which is probably driven by El Niño-like conditions. And El Niño is mostly a natural event that’s been occurring as long as people have been on the planet, and probably before then. People want like, “Humans are eight percent responsible.” But it’s really hard to say for sure in that regard.

I’m concerned with sea level rise: even if the storms don’t change at all with its intensity, if, say, the sea level is 6 inches higher than it used to be, you’re going to get more inundation — especially where the coast slopes up very gradually. And also I think there’s a lot of evidence showing that these storms will bring more rain. Obviously Florence and Harvey are extreme examples of that, but long-term that is something we expect to see.

What else do you want people to know about Willa?

It’s a serious storm, it’s going to make landfall tomorrow. You have a Florence, and an Irma, and people think, “Oh, you have two weeks notice that a hurricane’s coming.” And that’s not always the way it is. Sometimes these storms come very quickly — and certainly we saw that with Michael and with Willa, too. The storms that come in and do these right hooks into Mexico this time of year are pretty common, but obviously this one is going to be quite strong. So we’re just going to have to hope and pray it that it weakens before it hits. We’ve got a little over a day. If people happen to be there, follow the advice of local emergency management, they know the storm is out there and will be the best people on the ground to provide advice about what to do.