Will the Bermuda High help us again this storm season?

Sun Sentinel

Whether the Bermuda High will punish or protect Florida during hurricane season remains unknown. Washed out by a winter system over the U.S. Southeast, it’s for now a mushy blob of warm air, so diluted that it’s hard to tell where it’s centered.

“Currently it’s so weak that it’s barely detectible,” meteorologist Robert Molleda of the National Weather Service in Miami said Monday, during the Governor’s Hurricane Conference in Fort Lauderdale.

But that will change. It’s expected to intensify over coming weeks and reach peak strength during the summer. Then it will become the primary atmospheric feature that dictates whether hurricanes strike the U.S. coast or the Caribbean, or scoot out to sea.

Generally centered over the Western Atlantic, the Bermuda High is one of the main reasons Florida has enjoyed a record seven seasons without any hurricane strikes, either bouncing storms to the south or allowing them to curve north.

On the other hand, it was the major force that pushed Hurricanes Charley, Frances, Ivan and Jeanne toward Florida in 2004 and Hurricanes Dennis, Katrina and Rita toward the state in 2005.

When it’s strong, the Bermuda High creates an enormous clockwise wind circulation over the ocean, which pushes storms to the west or northwest in this general direction. But where it’s centered has a crucial bearing on where, specifically, storms go, as they tend to churn along the system’s outer edges.

For instance, last year Hurricane Leslie hugged the system’s western perimeter, curved north and hit Newfoundland, Canada. Hurricane Isaac, meanwhile, followed the edge into the Gulf of Mexico and ultimately into Louisiana.

Even when robust, the system “shifts east and west and weakens and strengthens,” making long-range forecasts difficult, said Steve Letro, a retired weather service meteorologist based in Jacksonville.

Hurricane paths are also influenced by other atmospheric forces, such as low-pressure systems and wind currents. “We don’t know how these patterns will interact with each other,” he said. “That’s what makes forecasting hurricanes so difficult.”

Although climatologists can predict in advance whether the hurricane season will be slow or busy, they can’t project which regions are most vulnerable. That’s because it’s unknown what steering currents will be at play until a storm is five to seven days from landfall.

“Even then we might not know where a storm is headed until it’s about three days out,” Molleda said.

Just the same, based on history, there’s no question Florida, the Gulf Coast and the Mid-Atlantic stand a good chance of being hit each year, he added.

The Governor's Hurricane Conference helps emergency managers, forecasters, first responders and government officials gear up for the upcoming storm season.

Senior hurricane specialist Richard Pasch of the National Hurricane Center said when storms emerge this year, don’t expect to see large swings from advisory to advisory in the track or intensity forecasts.

Forecasters try to avoid “flip-flopping” or the “windshield-wiper effect” when making their projections, he said. “Our credibility is subject to damage if we make big changes from forecast to forecast.”

The problem is computer models occasionally make big changes. When that happens, specialists make small adjustments but note their forecasts hold a large degree of uncertainty. Forecasters don’t put confidence in a prediction until the models are in agreement, Pasch added.

“We look for consistency,” he said.

For those who monitor the models, the top performers last year were the European and the GFS models, Pasch said. The HWERF and UKMET performed “fairly badly,” he added.





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