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The United States hasn\u2019t experienced the landfall of a Category 3 or larger hurricane in nine years \u2013 a string of years that\u2019s likely to come along only once every 177 years, according to a new NASA study.
\n\n\n\nThe current nine-year \u201cdrought\u201d is the longest period of time that has passed without a major hurricane making landfall in the U.S. since reliable records began in 1850, said Timothy Hall, a research scientist who studies hurricanes at NASA\u2019s Goddard Institute for Space Studies, New York.
\n\n\n\nThe National Hurricane Center calls any Category 3 or more intense hurricane a \u201cmajor\u201d storm. The last major storm to make landfall in the U.S. was Hurricane Wilma on Oct. 16, 2005 \u2013 the fourth major storm landfall of that year, which was the most active Atlantic hurricane season on record. Of course, storms smaller than a Category 3 have made landfall with destructive results, such as Hurricane Sandy in 2012.
\n\n\n\nHall and colleague Kelly Hereid, who works for ACE Tempest Re, a reinsurance firm based in Connecticut, ran a statistical hurricane model based on a record of Atlantic tropical cyclones from 1950 to 2012 and sea surface temperature data. While hurricane records stretch back to 1850, the data becomes less complete prior to 1950, Hall said. The study was published recently in Geophysical Research Letters.
\n\n\n\nThe researchers ran 1,000 computer simulations of the period from 1950-2012 \u2013 in effect simulating 63,000 separate Atlantic hurricane seasons. They found that a nine-year period without a major landfall is likely to occur once every 177 years on average.
\n\n\n\nWhile the study did not delve into the meteorological causes behind this lack of major hurricane landfalls, Hall said it appears it is a result of luck.
\n\n\n\n\u201cThe last nine hurricane seasons were not weak \u2013 storms just didn\u2019t hit the U.S.,\u201d Hall said. \u201cIt seems to be an accident of geography, random good luck.\u201d
\n\n\n\nWhen 2014 passed without a major hurricane landfall, the period from 2006-2014 surpassed the previous record for an absence of known major hurricane landfalls in the U.S., which occurred from 1861 to 1868. The researchers became curious about the probability of nine years passing without a major landfall.
\n\n\n\nThe nine-year period stands out, too, because it immediately followed the most active Atlantic hurricane season on record. As major hurricanes Dennis, Katrina, Rita and Wilma all hit the U.S., debate intensified about how global warming might drive hurricane activity.
\n\n\n\nHall said the past nine years show why there are still questions about the connection between hurricanes and the warming of Earth\u2019s atmosphere and ocean.
\n\n\n\n\u201cHurricanes respond in complicated ways to their environment,\u201d Hall said. Regarding the larger climate change-hurricane question, he said, \u201cIt\u2019s one of the areas of climate change research where reasonable people can still disagree.\u201d
\n\n\n\nA trickier problem than simply deriving the odds of such a \u201clandfall drought\u201d is trying to predict when the drought might end. Even though a long period of time has passed, the probability that any given year will end the drought is still the same every year, Hall said.
\n\n\n\nThink of it this way: If you flip a coin and it comes up heads nine times in a row, there is still a 50-50 chance that the 10th flip will come up tails. Hall and Hereid\u2019s statistical analysis found that in any given year there is a 39 percent probability of one or more major hurricane landfalls on the U.S and that that probability does not depend on the drought length. So what are the chances of this historic period coming to an end in 2015, based solely on the odds of the historical record? Thirty-nine percent, Hall said.
\n\n\n\n\u201cEach year is roughly independent of the year before,\u201d Hall said. \u201cThere are known signals, and natural cycles, and possibly human-induced influences. But for the most part, they are independent, especially for the rare intense landfalls.\u201d
\n\n\n\nContact:
\nLeslie McCarthy
Goddard Institute for Space Studies, New York
\n212-678-5507
leslie.m.mccarthy@nasa.gov
Patrick Lynch
NASA's Goddard Space Flight Center, Greenbelt, Maryland
\n301-286-3854
patrick.lynch@nasa.gov