A Hurricane Is Not a Point on a Map
A hurricane is not a point on a map.
It is not an object that exists in space and time. Rather, it’s a huge catharsis—a brief, explosive event when nature’s forces combine to spin off the ocean’s heat into wind. Over its brief life span, a hurricane expends the power of ten thousand nuclear bombs. It’s a spectacular display of thermodynamics in a complex, evolving, moving system.
Like a cancer, a hurricane is a lethal distortion of the stuff of everyday life. The earth’s winds harmlessly swirl about us, creating patterns in the clouds, kicking up waves for surfers, and nudging planes around the planet. All these heavenly movements are tendrils of much larger systems, like the jet streams that forever flow east, caught up in the rotation of Earth. Thanks to the jet stream, winter storms always pound New England in February when arctic air from Canada drifts south over the plains, gets swept east in its current, and is carried to the warmer air over the Atlantic Ocean.
Although the earth’s meteorological picture is as vast as the planet itself, it is very sensitive, prone to disruption, fickle. A butterfly-wing-like change in pressure or temperature in one place can cause a small piece of the continuum to break away from the mainstream like a recalcitrant teen. It often fades into the ether. But sometimes, when conditions are right, it can escalate exponentially, causing astounding damage to anything in its path.
Perhaps to domesticate these mighty systems, we give them names—Katrina, Sandy, Mitch, Joaquin. We mark them on our maps and say this is where she is. We draw a line and say this is where he will go. As if one day, a storm named Katrina rose out of the Gulf of Mexico like a Japanese monster hell-bent on ravaging New Orleans. As if you could put a beacon on her and track her every move as she made her way to her target. As if there were some kind of motive behind the destruction.
TROPICAL DEPRESSION ELEVEN FORECAST/ADVISORY NUMBER 1: 0300 UTC MON SEP 28 2015: TROPICAL DEPRESSION CENTER LOCATED NEAR 27.5N 68.7W AT 28/0300Z. PRESENT MOVEMENT TOWARD THE NORTHWEST AT 2 KT. MAX SUSTAINED WINDS 30 KT WITH GUSTS TO 40 KT.
Every hurricane begins as an atmospheric low, or depression, in the bottom layer of the earth’s atmosphere—the troposphere—which reaches up to seven miles above the planet’s surface. The low acts like a vacuum, pulling up warm, moist air from the ocean, which spirals around it in a counterclockwise direction in the Northern Hemisphere. If conditions are right—plentiful warm, humid air—the currents corkscrew upward around the low pressure zone at increasing speeds. When that heated air hits the much cooler upper atmosphere, it condenses, shooting out of the hurricane’s top like a whale’s spout, away from the center, and falls to earth as rain.
Feeding on the temperature and humidity differential between the hot ocean and the chilly upper atmosphere, the tropical storm thrives. Air currents around the center pick up heat, and with it, speed, as the center’s pressure drops even lower, intensifying the cycle. “Warmest climes but nurse the cruellest fangs,” wrote Herman Melville.
Joaquin was born as a tropical depression off the Canary Islands, three thousand miles east of Puerto Rico, a birthplace strange and rare for tropical cyclones because it was so far north. Designated Tropical Depression Eleven, it remained a loose cluster of showers that meandered across the North Atlantic toward the Caribbean. Forecasters at the National Hurricane Center in Miami ran their computer models and concluded that the system would dissipate. Over the course of a few weeks that September, however, Eleven defied the odds to become a cohesive system.
Even as Joaquin matured, dozens of computer models at the NHC in Miami predicted its demise. Some didn’t, but they were dismissed as outliers. On Monday, September 28, the day before El Faro departed from Jacksonville, the NHC issued an advisory: “The forecast for T.D. Eleven is to maintain tropical depression status while drifting slowly NW and will likely dissipate by the end of the week due to unfavorable winds aloft.” When Joaquin failed to comply, it took NHC forecasters by surprise.
In spite of a moderate shear—competing crosswinds that most forecasts predicted would blow it apart—at midnight on September 29, Eleven evolved into Tropical Storm Joaquin.
TROPICAL STORM JOAQUIN/ADVISORY NUMBER 6: 0900 UTC TUE SEP 29 2015: TROPICAL STORM CENTER LOCATED NEAR 26.6N 70.6W AT 29/0900Z. PRESENT MOVEMENT TOWARD THE WEST AT 4 KT. MAX SUSTAINED WINDS 35 KT WITH GUSTS TO 45 KT.
Throughout Joaquin’s evolution from depression to hurricane, the NHC could only guess at how it would develop, and what path it would take. The center issued discussions—carefully worded explanations of its forecasts of the storm system’s path and intensity. Embedded within these discussions were clear admissions of ambivalence: “There is considerable uncertainty among major models with the details of track . . . intensity and timing not only of Joaquin, but also the surrounding environment,” the center wrote at 2:47 p.m. EDT on Tuesday, September 29.
The same uncertainty was included in its weather discussion issued thirteen hours later.
Uncertainty in forecasting can be quantified. When models contradict one another, uncertainty is expressed as a probability.
In the course of everyday life, we don’t often encounter uncertainty. Gamblers and hedge funders may weigh odds all day, but most of us aren’t sure what to do if someone says she’s 30 percent sure she’s wrong. How do you process that, especially in a world where so many decisions are made for us by technology?
“If the definition of wisdom is understanding the depths of your own ignorance, meteorologists are wise,” says Kerry Emanuel, an MIT professor who has dedicated his life to understanding weather and climate. “It’s wise but it’s a wisdom that is not recognized. If you say there’s a lot of uncertainty in this, in the modern world, it’s translated as You don’t know anything.”
Due to uncertainty, prudent mariners follow the 3-2-1 rule: Three days ahead of a hurricane’s forecasted position, stay three hundred miles away; two days ahead, keep out of a two-hundred-mile radius of its projected center; one day ahead, stay one hundred miles away from its eye in all directions. The rule is based on the fact that hurricane paths are erratic and unpredictable, so it’s smart to give the system a wide berth.
But mariners often need to make binary decisions based on nebulous weather forecasts. On October 24, 1998, the elegant Fantome, a 679-ton staysail schooner built in 1927, departed Honduras for a six-day Windjammer cruise. A thousand miles away, Hurricane Mitch rumbled in the Caribbean Sea. As Mitch picked up strength, the captain of the Fantome got nervous and discharged his passengers in Belize City, then headed north toward the Gulf of Mexico to outrun the storm.
Forecasting Mitch proved extremely difficult due to weak steering winds, but the official NHC prediction, issued with multiple caveats, was that the storm would go north toward Mexico’s Yucatan Peninsula. When the Fantome’s captain received that forecast, he hove to and headed south, unwittingly right into the hurricane’s path, which, contrary to forecasts, took a left turn toward Central America. On October 27, fighting hundred-mile-per-hour winds and forty-foot seas, the Fantome was lost forty miles south of the hurricane’s deadly eye wall.
Slow and unyielding, the Category 5 storm’s winds and rains killed more than eleven thousand people in Honduras, Nicaragua, El Salvador, and Guatemala, making it the second-deadliest storm in the Atlantic’s history.
HURRICANE JOAQUIN FORECAST/ADVISORY NUMBER 11: 1500 UTC WED SEP 30 2015: HURRICANE CENTER LOCATED NEAR 24.7N 72.6W AT 30/1500Z. PRESENT MOVEMENT TOWARD THE SOUTHWEST AT 5 KT. MAX SUSTAINED WINDS 70 KT WITH GUSTS TO 85 KT.
Weak, meandering, dispersed Joaquin was precisely the kind of storm the NHC has trouble forecasting, says James Franklin, director of the center, as we sit in his Miami office a year and a half later. James has two MIT degrees, rimless glasses, and a quiet, analytical manner. He speaks in complete paragraphs. But his quiet demeanor belies an intrepid soul. James used to fly in NOAA Hurricane Hunters, straight into tropical storms. The Gulfstream IV is a high-altitude jet that flies in and around