Satellite image
captured on October 31, 2012 as Hurricane Sandy’s circulation was winding down
over Pennsylvania. (Photo was taken by NASA GOES Project).
2012 is being named one of the most active hurricane
seasons ever. There
were 19 named tropical storms this year in the Atlantic Ocean basin tying 2012
at third for most named-storms in recorded history. The
top spot goes to the 2005 season, which saw 28 named storms. While being one of the busiest on record, the
2012 season also saw weaker-than-average cyclones and began earlier than usual.
The United States has not been hit with a
major hurricane since 2005, by far the longest respite on record. While major
hurricanes were scarce this year, storms still caused major damage,
particularly Hurricane Sandy. That storm killed 125 people in the United
States, and another 71 people in the Caribbean, including 54 in Haiti.The large number of hurricanes seen this season resulted, in part, from above-average surface temperatures throughout the Atlantic, conditions which help cyclones form. Temperatures reached about 6 degrees Fahrenheit (3 degrees Celsius) above average this summer. Also, air higher up in the atmosphere also got warmer than usual. This helped to cap the storms' strength; hurricanes intensify the most when the upper atmosphere stays cool. The difference between the warm surface and cool atmosphere provides strength to cyclones, which function like giant heat engines.
In its first hurricane season forecast, made before the season
began, the National Oceanic and Atmospheric Administration predicted nine to 15
named storms. Then, in August, the organization upped its prediction to 12 to
17 named storms, with five to eight of those becoming hurricanes. The revision
was based on changes to climate patterns that affect storm formation. A
tropical storm becomes a hurricane once its top winds hit at least 74 mph (119
kph). The 19 named storms this season beat even the revised prediction. It's
relatively unusual to have more storms than forecast. The underestimate can be
blamed on El Niño, or rather, the lack of El Niño, when Hurricane Sandy formed.
Forecasters predicted that this weather pattern, characterized by cool surface
temperatures in the Pacific Ocean, would have developed by the fall. But it
didn't. Therefore, cyclone activity continued longer than expected in the
Atlantic, unperturbed by El Niño, which spawns high level winds that stream
eastward and can disrupt the swirling motion that gives a developing storm its
power.
Global warming likely isn't to blame for the increase in hurricanes. Many climate models suggest that increased temperatures could lead to
fewer, but stronger hurricanes worldwide, essentially the opposite of
what we saw this year.
Better technology also allows us to detect more hurricanes than in
the past. In the past few decades, satellites have significantly increased the
detection of short-lived tropical storms, i.e. ones that last fewer than 36
hours.
This year's season ended with Hurricane Sandy, which caused widespread devastation thanks to a tremendous storm surge throughout New Jersey and New York. Sandy will go down as the second costliest storm in U.S. history. This storm was unusual, as the first storm to retain hurricane strength north of the jet stream, the wind pattern that moves air from west to east across North America and into the Atlantic. Sandy also registered the lowest barometric pressure in the history of the Northeast. Once it moved north of the Gulf Stream, Sandy interacted with a mass of cold air moving east across the continent, causing it to transition to an extra-tropical storm and wreak so much devastation.
Scientists are still studying Sandy to understand how it formed,
and whether or not climate change might have contributed. It could be a freak
thing, or we could be going into a new climate regime where we're likely to see
more impacts like this in the future.
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