Sunday, May 17, 2015

NASA: "No Major U.S. Hurricane Landfalls in Nine Years: Luck?"

From NASA:
The United States hasn’t experienced the landfall of a Category 3 or larger hurricane in nine years – a string of years that’s likely to come along only once every 177 years, according to a new NASA study.

The current nine-year “drought” 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’s Goddard Institute for Space Studies, New York.

The National Hurricane Center calls any Category 3 or more intense hurricane a “major” storm. The last major storm to make landfall in the U.S. was Hurricane Wilma on Oct. 16, 2005 – 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.
Hall 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.

The researchers ran 1,000 computer simulations of the period from 1950-2012 – 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.

While 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.

“The last nine hurricane seasons were not weak – storms just didn’t hit the U.S.,” Hall said. “It seems to be an accident of geography, random good luck.”

When 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....MORE
Two quibbles. First up, when Sandy made landfall in New Jersey it was what is known as a “post-tropical cyclone” rather than a hurricane. The problem was that it arrived at both the daily high tide and at the monthly full-moon high tide meaning the storm surge was as big as would be expected from much stronger storms.

Secondly in the story above Mr. Hall says “The last nine hurricane seasons were not weak..." which is not completely accurate. Both by number and by a rough measure of total strength (wind speed x duration) known as Accumulated Cyclone Energy, the early to mid 90's were a more active period:
Both charts via Weatherbell.

That's not to say we haven't been lucky, just that something appears to have changed from earlier periods.
And definitely not to diminish Sandy, it was a monster storm:

NOAA GOES-13 image of Sandy at 6:02 a.m. EDT Tuesday (Oct. 30).