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Get ready to 'hunker down'

Forecasters expect another active hurricane season, spawned by La Nina and above average water surface temperatures.

By GRAHAM BRINK
Published March 13, 2006

It looks more and more like another nerve-racking hurricane season.

Sea surface temperatures are above average, La Nina has returned and the Atlantic Basin remains in an "up" cycle for storms.

"There is no reason not to expect a real active season," said Hugh Willoughby, a renowned hurricane researcher at Miami's Florida International University.

Longtime hurricane forecaster William Gray predicted an above-average season, with 17 named storms, nine of them hurricanes and five of those Category 3 or higher. He predicted at least one major hurricane would hit the United States.

Those numbers are likely to change as forecasters analyze updated data in the next few weeks. The National Oceanic & Atmospheric Administration is expected to issue its 2006 seasonal Atlantic hurricane outlook on May 22nd.

But some of the facts won't change.

The Atlantic Basin - the Atlantic Ocean, Caribbean Sea and Gulf of Mexico - remains in a hurricane "up" cycle that began in 1995. What exactly causes the cycles remains a mystery. Theories suggest shifts in major Atlantic currents and natural changes in water temperatures and salinity levels.

For the 25 years before 1995, an average of fewer than nine named storms formed in the Atlantic region. The numbers increased by about 40 percent over the next 10 years.

The results were particularly pronounced the last two seasons, when a total of 42 named storms formed in the Atlantic Basin. Eight hurricanes struck Florida in those two years.

Thanks to Hurricane Katrina, the 2005 season was also the deadliest in the United States since 1928, when a Category 4 storm breached the levees around the Lake Okeechobee, killing an estimated 2,500 to 3,000 people.

Even more bad news: Up cycles tend to last a bit longer than the down cycles, Willoughby said. The current cycle is expected to last another 20 or so years.

"Maybe even 30 years," Willoughby said.

NOAA scientists confirmed in January that La Nina was back.

It may have even been around last fall, helping prolong the 2005 season.

La Nina occurs with a cooling of sea waters in the east-central Pacific Ocean. The phenomenon is expected to help continue the drought in parts of the South and Southwest and bring additional rain to the Northwest and the Tennessee Valley area.

Forecasters emphasized that it is too early in the year to determine what affect, if any, the current La Nina will have on the 2006 hurricane season.

"The La Nina effect tends to change in the late spring," said Chris Landsea, science and operations officer for the National Hurricane Center in Miami. "That makes it tough to make an accurate assessment about what influence it will be having in the peak of hurricane season in August and September."

Historically, the phenomenon is linked to busier hurricane seasons in the Atlantic Basin. During La Nina, more named storms form in the deep tropics from weather systems that move off the Africa, according to the Climate Prediction Center. The systems are more likely to become major hurricanes that threaten the United States.

In a normal year, crosswinds prevent many systems from strengthening into tropical storms. The winds also shear or tear apart many of the systems that do strengthen into tropical storms. La Nina inhibits the formation of those storm-destroying crosswinds.

To form and survive, hurricanes need the winds to be fairly uniform throughout the atmosphere, meteorologists say. La Nina helps create those conditions by expanding the area of low wind shear.

La Nina typically occurs every three to five years. Once it is established, it often lasts a year or two. La In recent memory, La Nina plagued the 1999 season, which produced 12 named storms, including eight hurricanes and five Category 4 hurricanes, a record at the time.

"With La Nina, you can expect not only more storms than average, but stronger storms, as well," Landsea said.

Last year's record season occurred, in part, because of unusually warm ocean temperatures.

Tropical storms need fuel to thrive. Warm waters provide that fuel.

Last year the waters around many parts of the Atlantic Basin were 4 degrees warmer than normal.

It doesn't sound like much. But combined with warm waters, favorable steering winds and weak shear, it creates an ideal scenario for lots of storms.

Part of the reason for the warmer waters was that the Bermuda High, a system of high pressure, was exceptionally weak in the winter of 2004-2005 and did not provide the usual cooling of Atlantic Basin waters.

Essentially, the waters started off above average and nothing happened to prevent them from getting even warmer.

If there is a silver lining this year, it might be that the Bermuda High has been stronger the past few months. The trade winds have stirred up the Atlantic and cooled the sea surface.

The temperatures remain slightly above normal, but not as high as the previous year, Landsea said.

"That's the good news," he said.

The bad news: If La Nina minimizes the wind shear, the storms that form will be able to thrive. Then it comes down to which way the steering currents guide the storms. The last two years, the currents have driven a record number of storms toward Florida.

"In general, Florida gets hit a lot," Landsea said. "But what we've seen the last two years should not continue."

Graham Brink can be reached at 727 893-8406 or brink@sptimes.com

[Last modified March 13, 2006, 17:03:02]