The 2011 Atlantic hurricane season, which begins June 1, looks to be another above-average year, federal forecasters say, adding that residents along the Gulf and East Coast should make sure now that they know what to do if ordered to evacuate.
In an outlook released May 19, forecasters at the National Oceanic and Atmospheric Administration's Climate Prediction Center are calling for a 70 percent chance of 12 to 18 storms with tropical-storm-force winds or higher.
Of these storms, which would receive names ranging from Arlene to Sean, six to 10 are expected to grow into hurricanes. Three to six of these are likely to become major hurricanes, with winds in excess of 111 miles an hour.
The outlook brackets a similar forecast from Colorado State University's Tropical Meteorology Project.
In April, the most recent outlook, Philip Klotzbach and William Gray, who pioneered seasonal hurricane forecasts for the Atlantic, called for 16 named storms, of which nine are expected to become hurricanes. Of those nine, five are expected to become major hurricanes.
In a typical season, the Atlantic basin might see 11 named storms, six hurricanes, and two major hurricanes.
Last year, conditions in the Atlantic and Caribbean spawned 19 named storms, the third-highest number on record, according to Jane Lubchenco, who heads NOAA. Twelve of those storms became hurricanes, the second-highest number of hurricane ever recorded in one season.
"The US was lucky last year," she said during a May 19 press briefing. Considering the number and severity of the storms, the US emerged with remarkably little damage.
Hurricane Earl, which for a time strengthened to a category 4 storm, the second-highest category, flirted with the US East Coast from North Carolina up to Maine. Hurricane Bonnie spun close to the ongoing efforts to control the Deepwater Horizon blowout, in the Gulf of Mexico near Louisiana.
"We cannot count on having the same luck this year," Dr. Lubchenco added.
Several broad factors are contributing to the amped-up outlooks, researchers and forecasters say.
Surface waters in the tropical Atlantic, where many storms form, remain warmer than normal for this time of year – about 2 degrees Fahrenheit above normal now, compared with 4 degrees F. above normal last year. Storms grow and feed on those warm waters.
In addition, the 2011 season falls within an active phase of a broader, multi-decade cycle of heavier and lighter hurricane activity.
And the Atlantic is still under the influence of the long arm of a waning La Niña, part of a cycle that includes El Niño.
This "El Niño/Southern Oscillation" is manifest in seesaw patterns in atmospheric pressure and ocean temperatures across the tropical Pacific. These changes affect broader atmospheric circulation patterns, in ways that favor hurricane formation during La Niña episodes.
NOAA's seasonal outlook says nothing about whether or how many hurricanes will make landfall – an aspect of hurricane forecasting that, for the most part, is still a gleam in the eye of researchers.
Hence the importance of everyone living in low-lying areas along the Atlantic or Gulf Coasts being ready to leave, to avoid the flooding a hurricane's storm surge can bring.
"It takes only one hurricane to wreak devastation," Lubchenco said.
Individual preparedness is critical, emergency managers say. For people who physically and financially can prepare, following through on those preparations when needed frees up limited resources to focus on people who can't help themselves. And those preparations – which include keeping important financial documents in a family's "go kit" – can smooth the recovery process.
Unfortunately, people can experience "hurricane amnesia," adds Craig Fugate, who heads the Federal Emergency Management Agency (FEMA) in Washington. He is referring to the long time spans that can elapse between landfalling hurricanes in any one location, and the tendency of people to forget how serious the storms can be.
The amnesia problem is especially acute along the Northeast coast, he suggests, because relatively few hurricanes have made landfall there over the past few decades.
In other cases, he continues, people will say they've experienced a hurricane and say that the experience wasn't too bad, when they actually have experienced only a hurricane's outer, tropical-storm-force winds.
"If you live along the Gulf Coast, if you live along the Atlantic Coast, you have your notice – it's going to be an above average season," he says.
And it starts June 1.