Saturday, October 08, 2016

Atlantic Hurricane Season is Seeing More Major Storms

Sept. 9, 2016

While the U.S. has been in a major hurricane drought since 2005, those top level storms have actually become more common in the Atlantic basin. The reason could be linked to rising sea surface temperatures — fueled in part by global warming — as seen in ocean buoy data collected along the U.S. coast.

Hurricane Wilma — which at one point was the strongest tropical cyclone ever recorded in the Atlantic basin — was the last major hurricane to pummel the U.S., roaring ashore in Florida as a Category 3 storm on Oct. 24, 2005. Since that date, no Category 3 or higher storm — what the National Hurricane Center defines as major hurricanes — has hit anywhere in the U.S.

But that streak is deceiving. The incidence of major hurricanes has essentially doubled across the Atlantic basin since 1970, potentially linked to rising sea surface temperatures there. It just happens that fewer of those storms hit the U.S.

Of course, in the decade since Wilma struck, plenty of other storms have had a major impact. Hurricane Ike and Superstorm Sandy were among the costliest storms on record, but neither was technically categorized a major hurricane. And Hurricane Hermine, though only a Category 1 when it recently hit Florida, caused significant damage. It also ended the state’s nearly 11-year streak without any hurricane making landfall.

In addition to the rise in major hurricanes in the Atlantic basin, the average number of named hurricanes each year has increased to about seven storms from five storms, though the exact reasons for this rise are still the subject of research.

Other ocean basins have also seen changes to their seasons. Landfalling typhoons have become more intense in the northwest Pacific while Hawaii has seen a string of hurricanes and tropical storms swing dangerously close to the island in recent years.

One notable quirk in the Atlantic basin is the lack of Category 5 storms. The Atlantic basin hasn’t had a Category 5 storm form since Hurricane Felix in September 2007. That’s not to say storms haven’t gotten close to Category 5 status, though. Last year’s Hurricane Joaquin had winds peak at 155 mph, just 2 mph shy of the threshold for being labeled a Category 5.

Natural changes like the Atlantic Multidecadal Oscillation as well as more familiar shifts like El NiƱo are responsible for some of the year-to-year fluctuations in the number of hurricanes. Other factors like dust from the Sahara that serve to limit the formation of storms can also have a major impact on an individual hurricane season.

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