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Harvey. Irma. Maria. Why is this hurricane season so bad?

Capital Weather Gang's Angela Fritz explains the four factors that are behind a busy 2017 Atlantic hurricane season. (Video: Claritza Jimenez/The Washington Post)

The 2017 hurricane season has been a full-on assault from Mother Nature. We are under siege, and our attackers have benign names like Harvey and Irma and Maria. But they are callous, powerful, indiscriminate, terrifying, destructive, merciless and relentless.

Is Earth trying to eject us from the planet? Again and again and again the harshest of winds and hardest of rains has pounded on the most-defenseless territories we have. The Caribbean islands, hanging out in open sea. The Florida peninsula, jutting out into danger. The Texas coastline, low-lying and concrete-laden. Nearly a full month of back-to-back-to-back disasters.

This hurricane season — not yet even close to finished — has generated more destructive, land-falling storms than the past few years combined. Four of this year’s monsters went on to become Category 4 or 5, and three of those made landfall in U.S. territory. The U.S. has never been hit by three storms this strong in the same season in modern records.

Hurricane Maria expected to pass close to the Carolinas next week

Hurricane Harvey seemed to spin up in an instant before hitting land on Aug. 26, only to come to rest for days over Southeast Texas and Southwest Louisiana. A mind-boggling 19 trillion gallons of rain fell in that storm, which triggered unprecedented flooding. Texas Gov. Greg Abbott estimates Harvey will cost the state up to $180 billion — more than epic Hurricane Katrina.

Hurricane Irma was one of the strongest ever recorded in the Atlantic Ocean. When Irma maintained 180 mph wind speeds for 37 hours, it set a record for most intense storm for such a long duration — anywhere on Earth. It made landfall Sept. 10, strafing the Florida Keys before terrorizing both Florida coasts in vastly different ways. It knocked out power to millions of people, and some are still waiting for the lights to come back on.

Hurricane Maria made landfall in Puerto Rico 10 days later as the strongest storm to hit the island since the 1928 San Felipe hurricane. It thrashed the U.S. territory with winds over 100 mph and more than 30 inches of rain. All of Puerto Rico lost power and was under flash flood warnings. The full extent of the damage, and the loss of life, might not be known for some time. It could take months to restore infrastructure.

All of this in just four weeks.

It spurs so many questions: Is this barrage random? Is it part of a natural cycle? Is it the result of climate change? Have we done this to ourselves?

Graphic: How much rain Maria dropped on Puerto Rico

Officials at the highest levels — who create, pass and sign the very policies that affect the environment — are bending over backward to dodge those questions. The political tension is palpable. 

“To have any kind of focus on the cause and effect of the storm; versus helping people, or actually facing the effect of the storm, is misplaced,” Environmental Protection Agency Administrator Scott Pruitt told CNN as Hurricane Irma approached Florida.

When the question was posed to President Trump on his way to visit hurricane-battered Florida, he replied: “We’ve had storms over the years that have been bigger than this.”

To our struggling politicians, Pope Francis offered some advice: Climate change is happening, and you have a “moral responsibility” to do something about it.

“Those who deny this must go to the scientists and ask them,” he said on a recent trip to Colombia. “They speak very clearly.”

If they continue to deny climate change, he added, “history will judge those decisions.”

This hurricane season is, indisputably, a nightmare. And it’s indisputable that climate change is affecting our weather. The fingerprint of climate change is on every storm, it’s in every raindrop and sunny day. It is a new, yet untested and ill-understood, factor in the way our planet works.

But there are additional elements that had to come together to create such a hellish year.

Hurricanes exist to cool the tropics. The vast majority of sunlight beats down in the 23 degrees north and south of the equator. Without something to disperse the energy toward the poles, Earth’s climate would become unbalanced, quickly.

These planetary heat engines sprout from relatively weak clusters of thunderstorms — waves of low pressure from the coast of Africa — and fester in the warm waters of the Atlantic. They feed on tropical moisture and the sun’s intense energy and, eventually, if they get large enough, will start to spin thanks to Earth’s top-like motion.

Hurricanes can form in rapid succession and travel thousands of miles across the Atlantic, like rail cars on a train track or airplanes lining up for takeoff. Because they can gain steam, spinning themselves up into monstrosities, it’s a trip that can end in the devastation of places like St. Croix, the Virgin Islands, Puerto Rico and Southwest Louisiana. One after the other.

We saw this alignment in 2005, and we’re seeing it again in 2017.

“This isn’t a random coming together,” said Gerry Bell, a hurricane climate specialist at NOAA. It’s a specific combination of environmental factors.

The Atlantic Ocean is in a pattern that’s particularly favorable for hurricanes. Every couple of decades, the pattern flips, but it’s been positive since about 1995.

Fear is in the water, spreading with new and viral efficiency

There have been some exceptionally big seasons in the past two decades. The extreme years tend to happen when the things that weaken hurricanes are not present — like El Niño and chaotic, hurricane-killing winds over the Atlantic Ocean. When those forces stand down, the favorable pattern goes to work.

Factor in some exceptionally warm ocean water, and it becomes nearly impossible to avoid a strong season.

“We are seeing some of the hottest ocean temperatures in the planet in the western Caribbean Sea,” said Michael Ventrice, a research meteorologist at the Weather Company. “This is like rocket fuel for developing tropical cyclones. A major concern for late-season development.”

But hurricanes need to make landfall to generate the kind of disasters seen so far this year. Steering winds determine their path, though they aren’t always as predictable as forecasters would like. Which Florida coast would receive Hurricane Irma’s landfall — Miami or the Gulf — was a result of uncertainty in the wind forecast. It hit near Naples, Fla., and went north, but the massive storm covered the entire state, knocking out power to millions and causing flooding and damage from the Florida Keys to Jacksonville and beyond.

The Florida Peninsula is only about 100 miles wide — a tiny distance on a global scale. Hurricane Irma was going to turn north somewhere near South Florida, forecasters knew that. But a few miles of deviation meant some people were spared while others were inundated with storm surge and damaging winds.

In the same way, Puerto Rico avoided Irma’s destructive inner core, only to be devastated by Hurricane Maria. These winds are fickle, but deadly.

If we zoom out to the big picture, though, the steering winds over the Atlantic Ocean have been very predictable this season. Unfortunately for all the humans who live there, the winds have been guiding hurricanes straight into the Caribbean islands and the Southern United States.

It’s a significant shift. For the past decade, those winds were coming from the west, pushing hurricanes away from land and out to sea, rendering them largely harmless.

“We were very fortunate, since 2005,” Bell said. “But it was just a matter of time before they were going to start making landfall again.”

This year is remarkably similar to 2005, when storm after storm exploded over the Caribbean and then made landfall. Hurricanes Katrina, Rita and Wilma are among the more memorable of that year.

The 2017 season is only half over. There will be more storms, and the wind isn’t going to change any time soon. At least one forecast company thinks this heightened level of activity will continue.

“I would be surprised if October wasn’t more active than normal, with one or more potential threats to the eastern Gulf Coast originating in the central or western Caribbean,” Ryan Truchelut, the president of WeatherTiger, predicted.

More potential threats, more hurricanes. More lives lost and more destruction.

“A lot of people have already been through a lifetime of impacts, but there are going to be more storms, we know that,” Bell warned. “They have to stay prepared.”

Jason Samenow contributed to this report.