A natural buffer zone of wind shear and cooler ocean temps has been found to form along the U.S. East Coast during periods of greater Atlantic hurricane activity, weakening storms as they approach land and making them less destructive when they make landfall, a new study has shown.
The link between this so-called “buffer zone” and both active and inactive periods of Atlantic hurricane activity was detailed Wednesday in a paper by NCEI (NOAA) scientist, Jim Kossin, and published in the science journal, Nature.
The study found that this protective barrier is made up of vertical wind shear and cooler ocean temperatures, and tends to form along the U.S. East Coast during periods of greater hurricane activity.
Kossin says this barrier could even be responsible for the present “drought” of major hurricane landfalls in the United States.
“During periods of greater hurricane activity, the sea surface temperatures are warmer and the wind shear is weaker in the tropical Atlantic,” says Kossin. “Likewise, during periods of low activity, the sea surface temperatures are cooler and the wind shear is stronger there. But, the opposite is true when we look near the U.S. coast. When conditions in the tropical Atlantic are good for hurricane intensification, they are bad for it near the coast and vice versa.”
A hurricane’s intensification depends on a combination of sea surface temperatures and vertical wind shear; the warmer the waters and weaker the wind shear the better for intensification. But the study found that when conditions are ripe for creating hurricanes, sea surface temps decrease and wind shear strengthens along the U.S. coast, creating the buffer zone.
“So, when the environment is good for making strong hurricanes in the tropics, those hurricanes crash into more hostile conditions if they approach the U.S. coast, which weakens them,” NOAA said in a press release announcing the findings from the study. “In this way, the pattern creates a hurricane buffer zone along the coast during periods of high activity. According to historical records from 1947 to 2015, hurricanes were roughly twice as likely to intensify along the U.S. East Coast when the buffer zone wasn’t present. And, they were two to three times more likely to rapidly intensify—by 15 knots or more in 6 hours—without the wind shear and ocean temperature buffer.”
The buffer zone may have played a role in October when Hurricane Matthew approached Florida.
“While Matthew’s rains were devastating for some areas, the buffer zone helped weaken the storm from a Category 4 as it advanced on Florida to a Category 1 when it officially made landfall in South Carolina. By keeping higher wind speeds at bay, the buffer zone likely helped prevent further compounding damages from Matthew,” NOAA explains.
Kossin believes the absence of the buffer zone had an even greater impact on major hurricanes. Without it, major hurricanes are seen as being two to four times more likely to intensify and three to six times more likely to intensify rapidly.
“This presents major implications for forecasters, as rapid intensification near the coast is difficult to predict and shortens public warning time,” NOAA says.