Busy but weak -- hurricane season sent mixed message
MIAMI -- Hurricane season 2012, which officially ends Saturday, will go down in history as the year of Superstorm Sandy, which carved a path of death and devastation from the Caribbean to the Jersey Shore.
Scientifically speaking, it also was notable for something it was not: intense. For the third consecutive season, the tropics churned out what not long ago would rank as an abnormally large number of storms -- yet curiously only one of 19 managed to reach Category 3 strength.
And it wasn't Sandy. It was otherwise forgettable Michael, which spent all of a half-day with its maximum winds above the "major" benchmark of 111 mph before spinning off into oblivion in the far-off Atlantic Ocean.
By the old-school yardstick of named storms, 2012 ranked among the busiest hurricane season on record. By broader and more sophisticated measures, it was sort of middling.
"We had a large number of storms but most of them did not amount to much," said Chris Landsea, science and operations officer for the National Hurricane Center.
"It was very unusual," said Phil Klotzbach, a research scientist at Colorado State University who teams with climatologist William Gray on closely watched annual hurricane forecasts. "For major hurricanes, it was one of the quietest years in the last 24 years."
Despite two close and soggy calls, it also went down as a lucky seventh consecutive landfall-free year for South Florida.
Overall, this year's tropical output may only muddy the climate-change debate reopened as a result of Sandy slamming the heavily populated, rarely-hit northeastern United States.
With the media capital of America at the center of its path, Sandy may have been among the most hyped hurricanes in history. Unfortunately, it largely lived up to the billing, filling New York City streets and subways with seawater, inundating quaint towns along the Jersey Shore and killing 115 people. The storm, which earlier killed more than 70 people as it raked across Haiti, Cuba and the Bahamas, also pulled the issue of global warming out of the political deep freezer. New York City Mayor Michael Bloomberg, echoing environmental groups, said Sandy's destruction had underlined the concerns of rising sea levels and stronger storms.
Sandy struck the Northeast as a rare but not unprecedented hybrid of tropical hurricane and nor'easter winter storm, forecasters said. It was so powerful it reached the second-lowest barometric pressure reading ever recorded for a northeastern storm. The massive storm, added by seasonal high tides, pushed a record storm surge into Lower Manhattan and along the New York-New Jersey coast.
But sorting out how much of a role, if any, climate change may have played in a specific storm like Sandy or even in any given hurricane season may be impossible.
"From one season to the next, it's just not something we can see," said Brian McNoldy, a senior researcher at the University of Miami's Rosenstiel School of Marine and Atmospheric Science who writes a hurricane expert blog for The Washington Post. "It's something we may be able to see unfold over decades."
Complicating the debate, the prevailing theory about climate change impacts has been that that warming oceans would likely produce fewer but more intense hurricanes, he said.
In 2012 at least, McNoldy said, "That's the exact opposite that has happened."
Hurricane Michael is the only storm that officially, and briefly, clocked in Category 3 intensity during the six-month season. The hurricane center's Landsea said Sandy, which struck Santiago de Cuba as a powerful Category 2 hurricane, potentially could be upgraded after annual post-season analysis.
But even if that happens, the percentage of storms making it to major status this season would remain unusually low. Typically, one of every four to five hurricanes reaches Category 3 strength or higher at some point in its life.
Scientists can't say for certain but a combination of factors may have contributed to tamping down intensity. A number of storms seemed to struggle with drier than normal air, they say, thanks to a more stubborn and heavier influx of Saharan dust.
Wind shear also weakened some storms. That happened despite a predicted El Nino global weather pattern, which generally produces stronger shear and fewer storms, never kicking in. Many preseason forecasts calling for an average or even below average number of storms had banked on El Nino to calm tropical development.
Instead, 2012 became the third consecutive year for the storm count hit 19, a total tied for the third busiest in records dating back to 1851. Ten storms became hurricanes, also above average. Only two years saw more storms: 1933 with 20 and 2005 with a stunning 28, including four that struck Florida in a six-week period.
But it was a season largely without strong hurricanes. By a broader measure called Accumulated Cycle Energy or ACE, a formula that weighs the duration and strength of storms, the season wound up a bit above average, ranking as the 11th most active in the last 30 years, Landsea said. That figure was bumped up a bit by never-say-die Hurricane Nadine, which formed, dissolved and reformed over nearly four weeks to become the fifth-longest enduring Atlantic storm on record. It was a nuisance only to the Azores off Africa.