WHY MONSTER STORMS SEEM MORE COMMON
Several factors behind proliferating Category 5s
They’re monsters of the Atlantic: deadly storms that reach wind speeds of 157 mph or higher. And we’ve seen two of them in two weeks.
Hurricanes Irma and Maria were a rarity. Only five other seasons have brought more than one Category 5 hurricane: 1932, 1933, 1961, 2005 and 2007.
Experts say that while the number of storms per year is steady, stronger hurricanes have increased in recent decades.
Of this year’s storm season, “it’s explainable to some degree, and to another degree we simply don’t know why it’s been so crazy busy,” said Jeff Masters, a hurricane expert at Weather Underground, a popular weather website.
Big storms
Only three Category 5 storms have hit the United States since record keeping began: The 1935 Labor Day hurricane
“Hurricanes are like bananas; they come in bunches.” Jeff Masters, Weather Underground
hit the Florida Keys and killed 600 people.
Hurricane Camille devastated the Mississippi coast in 1969, killing 256 and leaving $1.4 billion damage.
Hurricane Andrew, which hit South Florida in 1992, killed 43 and caused $30.5 billion in damage.
Hurricane Katrina in 2005 reached Category 5 in open water but hit the coast as a Category 3. Most estimates put the death toll in Katrina at more than 1,800 people.
The storm caused more than $100 billion in damage; some later estimates peg that number at more than $150 billion.
2005 remains the most active and intense hurricane season on record, spawning three Category 5 storms in addition to Katrina: Emily, Rita and Wilma.
Wilma was the last major hurricane to strike Florida before Irma made landfall earlier this month in the Florida Keys and then in Southwest Florida.
Hurricane Irma was a Category 4 when it hit the Florida Keys.
When there’s a spate of major hurricanes, people tend to wonder if we’re entering an era of bigger and more powerful storms, says Dan Kottlowski, a meteorologist at AccuWeather, a Pennsylvania-based company that provides forecasts.
“You know, the same thing was brought up after 1995 and again after the 2005 season. People said, ‘Oh my gosh, we had Katrina, Wilma, Rita’ — you know, all these Cat 5s,” Kottlowski said. “And again, I think we’ve been lucky over the past 10, 12 years or so, as far as the fact the tropics have been relatively quiet.”
Conditions ripe for storms
Two major factors are creating hurricane-friendly conditions in the Atlantic region, which includes the Caribbean Sea and Gulf of Mexico: warm water and a lack of wind shear.
Water temperatures have been about 3 degrees above normal this year in the Atlantic basin, forecasters note. And wind shear has been low.
Wind shear, which refers to fluctuations in wind speed or direction, is a storm killer. When you take away wind shear, hurricanes are more likely to form.
In addition, federal climate officials say there’s a good chance the La Nina weather pattern will officially be in effect by this fall or winter.
La Nina, characterized by colder temperatures in the Pacific around the equator, affects weather in the Atlantic hurricane region as well, in the form of less wind in the tropics and therefore more hospitable conditions for hurricanes.
Predicting how long La Nina might hang around is difficult, but it typically lasts about a year, sometimes as long as two years, experts say.
Other factors
Since 1995, we’ve been in a warming phase of a decades-long climate cycle that affects temperatures in the Atlantic. But with questions of climate, it takes a longer, bigger-picture view that requires decades of research to draw conclusions. Masters said there’s about 30 years of good hurricane data, which might sound like a lot but isn’t in the context of climate.
The brutal 2017 hurricane season is far from over, but already there are signs that next year could be a bad one as well.
With La Nina appearing to emerge, the long-term outlook favors another busier-than-average storm season, Masters said. “That’s my expectation, I think we’ll have another busy hurricane season next year,” Masters said. “Hurricanes are like bananas; they come in bunches.” Information from The Associated Press supplemented this report.