As we creep into the peak of hurricane season, many media outlets have dispatched reporters to the Caribbean and Gulf Coast to get first-hand accounts of the action. Maybe next season Matt Soniak can join them. (We’ll start saving). For now, his contribution to the national weather conversation is this Hurricane FAQ.
LET’S START SMALL. WHAT IS A HURRICANE?
Hurricanes are tropical cyclones that occur in the Atlantic Ocean and have winds with a sustained speed of at least 74 miles per hour. A tropical cyclone, in turn, is a storm system that develops in the tropics and is characterized by a low pressure center and thunderstorms that produce strong winds, rain, and storm surges. “Tropical cyclone” is a generic name that refers to the storms' geographic origin and cyclonic rotation around a central eye. Depending on their location and strength, the storms are called different things. What gets dubbed a hurricane in the Atlantic, for example, would be called a typhoon if it happened in the northwestern Pacific.
WHAT’S THE DIFFERENCE BETWEEN A HURRICANE AND A TROPICAL STORM?
Wind speed. When tropical cyclones are just starting out as general areas of low pressure with the potential to strengthen, they’re called tropical depressions. They’re given sequential numbers as they form during a storm season so the National Hurricane Center can keep tabs on them.
Once a cyclone’s winds kick up to 39 miles per hour and sustain that speed for 10 minutes, it becomes a tropical storm and the NHC gives it a name (more on that later).
If the cyclone keeps growing and sustains 74 mph winds, it graduates to hurricane.
ONCE WE CALL IT A HURRICANE, HOW DO WE CATEGORIZE IT?
We look to the Saffir-Simpson Hurricane scale, developed as a classification system for Western Hemisphere tropical cyclones in the late 1960s and early 70s by structural engineer Herbert Saffir and his friend, meteorologist Robert Simpson, who was the director of the NHC at the time.
When Saffir was working on a United Nations project to study low-cost housing in hurricane-prone areas, it struck him that there was no simple, standardized way of describing hurricanes and their damaging effects, like the way the Richter scale is used to describe earthquakes. He created a 1-5 scale based on wind speed and sent it off to Simpson, who expanded on it to include the effects on storm surge and flooding. Simpson began using it internally at the NHC, and then in reports shared with emergency agencies. It proved useful, so others began adopting it and it quickly spread.
HOW DOES THE SCALE WORK?
According to the NHC, the scale breaks down like this:
Category 1 storms have sustained winds of 74-95 mph. These “very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.”
Category 2 storms have sustained winds of 96-110 mph. These “extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.”
Category 3 storms have sustained winds of 111-129 mph. This is the first category that qualifies as a “major storm” and “devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.”
Category 4 storms have sustained winds of 130-156 mph. These storms are “catastrophic” and damage includes: “Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.”
Category 5 storms have sustained winds of 157 mph or higher. The catastrophic damage entailed here includes: “A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.”
While the Saffir-Simpson is useful, it isn’t the be-all and end-all for measuring storms. As NHC director Dr. Rick Knabb and senior hurricane specialist Daniel Brown pointed out recently on Twitter, the Center doesn’t “emphasize Saffir-Simpson Hurricane Wind Scale. Instead focus on specific hazards at your location…Doesn’t take major hurricane or even hurricane to have major impacts. Despite category, can have big impacts.”
IS THERE ANYTHING WORSE THAN A CATEGORY 5?
Not on paper, but there have been hurricanes that have gone beyond the upper bounds of the scale. Hurricane Wilma, which hit the United States in 2005, was the most intense hurricane ever recorded in the Atlantic, with winds peaking at 175 mph.
Hypothetically, hurricanes could up the ante beyond category 5 more regularly. The storms use warm water to fuel themselves and as ocean temperatures rise, climatologists predict that potential hurricane intensity will increase. Don’t expect the scale to change though. Both Saffir and Simpson have said that there’s no need to add more categories because once things go beyond 156 mph, the damage all looks the same: really, really bad.
HOW DO HURRICANES GET THEIR NAMES?
Since Europeans first came to the Americas and the Caribbean, hurricanes have been named using a variety of systems. First they were named after the Catholic saints. Later on, the latitude-longitude positions of a storm’s formation was used as a moniker, but that was a little too cumbersome to use in conversation.
Military meteorologists started giving female names to storms during World War II, and in 1950 the World Meteorological Organization adopted the practice. In 1979, the system was given a dose of political correctness: Male names were added to the list, as were French and Spanish names, reflecting the languages of Caribbean nations frequently affected by the storms.
Today, for Atlantic hurricanes, the WMO and NHC use six lists of 21 names (Q, U, Y and Z names aren’t used) that it cycles through every six years (for example, the 2013 names list will be used again in 2019), with the gender of the season’s first storm alternating year to year and the genders alternating down the list through the rest of the season. If there are more than 21 named storms in a year, as there were in 2005, the rest of the storms are named for letters of the Greek alphabet.
Names can be retired at the annual WMO meeting if a storm is particularly devastating, deadly or costly and further use of the name would be insensitive or inappropriate. The name is then struck from the list and a new one is chosen to replace it (yes, Sandy was retired at the most recent meeting).
Occasionally, a storm suffers something of an identity crisis and has its name changed. This happens when a storm dies down and then redevelops or when it crosses from one ocean to another. The first actively tracked and named storm to cross over like this happened in 1971. Hurricane Irene developed in the Caribbean Sea and made landfall in Nicaragua. The storm managed to maintain itself and cross over a low-lying area of the country and restrengthen in the Pacific Ocean, where it was renamed Hurricane Olivia.
If a storm forms in the off-season, it takes the next available name from either the next season’s list or the previous season’s, depending on the calendar date. A late 2013 storm would take one of this season’s names, for example, and an early 2014 storm would get a jump start on next season’s list.
WILL MY NAME BE A HURRICANE THIS YEAR?
If your name is Olga and there are enough named storms, then yes. The names on the list for the 2013 season are Andrea, Barry, Chantal, Dorian, Erin, Fernand, Gabrielle, Humberto, Ingrid, Jerry, Karen, Lorenzo, Melissa, Nestor, Olga, Pablo, Rebekah, Sebastien, Tanya, Van and Wendy.
WHAT KIND OF ACTION CAN WE EXPECT THIS SEASON?
In their most recent hurricane season outlook, NOAA and the NHC predicted a season with above-normal activity. Conditions like above-average Atlantic surface temperatures and a strong rainy season in West Africa (which produces wind patterns favorable to tropical storms and hurricanes) lead NOAA to predict a 70% chance of 13 to 19 named storms, 6 to 9 hurricanes and 3 to 5 major hurricanes (Category 3,4, or 5).
DO DISASTERS LIKE HURRICANES REALLY LEAD TO BABY BOOMS?
Everyone likes to think that when you’re stuck inside with no power, boredom leads people to the bedroom. The idea that natural disasters and birth rates are correlated go back to at least the 1965 New York City blackout, when the New York Times noted a “sharp increase in births” in several of the city’s large hospitals nine months afterwards.
The evidence for hurricane/snow/tornado/whatever babies is mixed, though. A few studies have found that natural and man-made disasters can influence the birth rate, and others haven’t. When disasters do come into play, the birth rate doesn’t always increase, and the reason for making babies is sometimes more complicated than just needing something to do.
A Penn State University study from 2002, for example, found that marriage, birth and divorce rates all shot up in the South Carolina counties that were declared disaster areas after Hurricane Hugo struck in 1990. With all three moving in the same direction, the researchers concluded that the stress and life-threatening danger from the storm provoked “significant and relatively quick action in [people’s] personal lives that altered their life course.”
In 2010, an international team of economists analyzed over a decade’s worth of birth data and hurricane and tropical storm advisories in 47 counties in the southern U.S. They found that “low-severity” advisories correlated positively with birth rates nine months later and that “high-severity” advisories correlated negatively. The differing birth rates following the two types of warnings, the researchers reasoned, was tied to the perceived danger and the things people normally do during them. During a low grade storm warning, people might stock up on food and hunker down in the house. After a while, they might get bored watching TV, or maybe the power goes out, and they head to the bedroom—in line with the popular prediction. In a more severe warning, though, people might be more concerned with gathering supplies, securing their homes and getting ready to leave the area. Even if they’re riding the storm out at home, the researchers think, they may be too worried or occupied to engage in romance.
So, will we see a lot of babiesnine months after one of this season’s storms next spring or summer? Maybe, but certainly not in all areas and not always because of the exact same reasons. The ties between catastrophe and conception are more complex than we might think.
SPEAKING OF RIDING OUT THE STORM, WHY DO PEOPLE INSIST ON DOING THAT?
Why do some people insist on staying in the path of the storm long after others have been evacuated, the roads have closed or flooded, and rescue is difficult or impossible? Why would they put their own lives and the lives of their rescuers at risk?
To answer that question, psychologists turned to the experts on the subject: the New Orleans residents who bore Hurricane Katrina’s wrath. The researchers found that there were a variety of factors that played into the decision to leave or not, a major one being finances and resources. “Leavers” usually had the money and transportation options to leave the city, and friends or relatives outside the storm’s path that they could stay with. “Stayers” usually had less financial assets, fewer or no transportation options to get out of the city, and little to no social network outside of it. Many of those who stayed simply didn’t have the resources to do otherwise and had no choice but to ride things out.
But money and places to stay weren’t the only things decisions were based on. The researchers also found that there were psychological and psycho-social factors—like a mistrust of outsiders (in the form of people from outside the city making the decision that residents shouldn’t stay); a desire to stay close to neighbors, friends and others from one’s community for support; and a perceived obligation to, in turn, support and assist others from the community—that influenced the decision to not leave.
The interviews with the people that stayed revealed that their motivations and actions were in line with what psychologists call the conjoint model of human agency, a framework of action built around interdependence between individuals and the idea that people make choices to adapt themselves to their environment. It’s a model that research often finds among working-class Americans, and here suggests that the stayers weren’t simply choosing not to act, but were acting—despite constraints—in a way that fit their environment and worldview.
HAS A HURRICANE EVER HIT [MY CITY]?
Maybe. Find out with this cool NOAA app that lets you track the paths of storms by name and location.
WHAT WERE THE LARGEST AND LONGEST HURRICANES?
The largest by diameter was last year’s Hurricane Sandy, which was somewhere between 820 and 1,000 miles wide, depending on who you ask and when they measured it.
The longest lasting hurricane is either an unnamed 1899 storm, sometimes called the San Ciriaco hurricane, that lasted 27.75 days, but was downgraded to a tropical storm before being upgraded to a hurricane again, or 1971’s Hurricane Ginger, which lasted 27 consecutive days as a hurricane.