Florida Keys News - Islamorada/KL Free Press
Wednesday, October 30, 2013
Quiet hurricane season foils forecasters

Forecasters have already begun the process of determining why this year's Atlantic hurricane season has been far quieter than expected.

"We're racking our heads," said Dr. William M. Gray, the atmospheric scientist who heads the hurricane forecast center at Colorado State University.

In April, CSU's Tropical Meteorology Project predicted 18 named Atlantic storms this year, including nine hurricanes and four major hurricanes. The National Oceanic and Atmospheric Administration's Climate Prediction Center also expected an active hurricane season, which runs from June 1 to Nov. 30.

The periodic climatic condition known as El Nino, which tends to break up hurricanes with wind shear, isn't around this year. Sea surface temperatures in the tropical Atlantic are high. And in West Africa, where the hurricanes often form, the monsoon season was strong, meaning plenty of moisture was able to move west off the continent and into the ocean. Taken together, conditions appeared ideal for storms.

In late May, NOAA called for a 70 percent chance of an above average hurricane season and just a 5 percent chance of a below average season.

Through last week, the 2013 Atlantic hurricane season had produced 12 named storms. That's about average. But only two of the storms, Humberto and Ingrid, became hurricanes, and they never grew stronger than Category 1.

To date, the Atlantic basin has seen the fewest hurricanes since 1982, said National Hurricane Center Public Affairs Officer Dennis Feltgen. The last year in which no major hurricane formed was 1994.

The likelihood that one will form before the end of the hurricane season is scant, Gray said. There has not been a major November hurricane in the Atlantic region since record keeping began in 1851.

There's no certainty as to the specific causes of this year's surprisingly inactive hurricane season. But both Gray and Feltgen said an unusual amount of dry air from high in the atmosphere over the tropical east Atlantic has sunk into the lower altitudes where hurricanes form.

Gray said he believes a dearth of wind blowing up from the equatorial region off of South America also has led to less cloud formation in eastern Atlantic. Those clearer skies have paved the way for the descent of the dry upper atmospheric air.

Coupled with surprisingly unexpected wind shear, which breaks up storms, the drier air created a gauntlet in the east Atlantic that most storms couldn't navigate, Feltgen said. Higher than usual amounts of atmospheric dust blowing off Saharan west Africa also helped keep the air dry.

Meanwhile, persistent low pressure over the Southeastern United States has also led to wind shear in the western Atlantic, impacting development in that area.

Only in the southwest Gulf of Mexico have conditions been what Feltgen called "marginally favorable for development this season."

Five of the 12 named storms this year originated in that area, including Hurricane Ingrid.

Despite the early predictions for an active year, 2013 is on the verge of becoming the first year since 1968 that no Atlantic basin storm has even reached Category 2 status.

"You can pretty well say this season has been a bust," Gray said. "We're going to have egg on our face for a long time."

rsilk@keysnews.com

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