During periods of greater Atlantic hurricane activity, a protective barrier of vertical wind shear and cooler ocean temperatures forms along the US east coast.
This weakens storms as they approach land, according to the study Hurricane intensification along United States coast suppressed during active hurricane periods by Jim Kossin, a scientist with National Oceanic and Atmospheric Administration (NOAA) and National Centers for Environmental Information (NCEI).
Hurricanes depend on warm sea surface temperatures to power their warm cores with heat and moisture. But vertical wind shear – changes in wind speed and direction from the surface to the top of the troposphere – removes the heat and moisture from a storm’s centre, disrupting the storm and potentially breaking it apart completely.
Atlantic hurricane activity
In the tropical Atlantic, where hurricanes develop, sea surface temperatures and vertical wind shear act together to either enhance or hinder hurricane intensification.
“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 US coast.
When conditions in the tropical Atlantic are good for hurricane intensification, they are bad for it near the coast and vice versa.”
Hurricane buffer zones
The period of high Atlantic hurricane activity over the past 20 years and the accompanying development of the buffer zone may help explain the present drought of major hurricane landfalls in the US.
The buffer might have come into play when Hurricane Matthew headed toward the country. Matthew’s rains were devastating for some areas, but the buffer might have come into play with hurricanes that weakened before landfall, including Hurricane Ike in 2008 and Sandy in 2012.
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