2012 One of the Most Active Hurricane Seasons
2012: A Year of Weather Extremes
This year's hurricane season officially ends today (Nov. 30) and will be remembered primarily for Hurricane Sandy, for obvious reasons. But Sandy was only the last hurricane in a very active — and unusual — season.
One of the busiest on record, the 2012 season also saw weaker-than-average cyclones and began earlier than usual, said Brian McNoldy, a researcher at the University of Miami.
There were 19 named tropical storms this year in the Atlantic Ocean basin tying 2012 at third for most named-storms in recorded history, McNoldy told OurAmazingPlanet. The top spot goes to the 2005 season, which saw 28 named storms. A storm is named once it attains tropical storm status, defined as a rotating, organized storm with maximum sustained winds of at least 39 mph (63 kph). [In Images: Hurricane Season 2012]
Two storms, Alberto and Beryl, spun up this spring before the official hurricane season start date of June 1, an unusual occurrence, McNoldy said. These resulted from warmer-than-average surface temperatures throughout the Atlantic. Beryl was the earliest second-named storm of any season since record keeping began in 1950, according to government records. (The official start date is a human-imposed one based on statistical averages of hurricane season starts. Likewise, another hurricane could arise after today's season end, although it isn't likely.)
Over the last 30 years, an average of 12.1 named storms, 6.4 hurricanes and 2.7 major hurricanes have occurred per year, McNoldy said. This year, 10 hurricanes appeared, but only one of them, Hurricane Michael, grew intense enough to rank as major (defined as Category 3 or stronger on the Saffir-Simpson scale). And Hurricane Michael only maintained this level of intensity for six hours, McNoldy said.
In fact, the United States has not been hit with a major hurricane since 2005, by far the longest respite on record, according to McNoldy.
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, according to the Associated Press. Hurricane Isaac also walloped the South in late August, causing a storm surge of up to 11 feet (3 meters) in some areas. Mainly, though, it poured down rain, dropping some 23 inches (58 centimeters) near Gretna, La., for example, according to the National Hurricane Center.
Blame it on the heat
The large number of hurricanes seen this season resulted, in part, from above-average surface temperatures throughout the Atlantic, conditions which help cyclones form, said Jeff Weber, a scientist with the University Corporation for Atmospheric Research in Boulder, Colo. Temperatures reached about 6 degrees Fahrenheit (3 degrees Celsius) above average this summer, he said.
However, air higher up in the atmosphere also got warmer than usual. This helped to cap the storms' strength, McNoldy said; 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, he said.
Nevertheless, this year's storms still packed a punch. Scientists use Accumulated Cyclone Energy, or ACE, to measure the intensity of a hurricane season; the measure quantifies the amount of energy contained in cyclonic winds, taking into account the number, duration and intensity of storms. The 2012 season finished with an ACE of 126.2, or about 137 percent of an average season. The median value from 1951 to 2010 is 92.4, as McNoldy noted in a piece he wrote for the Capital Weather Gang.