A hurricane season that was immensely kind to the United States ended quietly yesterday -- very quietly.
The season got off to a quick start but mysteriously fizzled in late September, with only one modest hurricane forming after Sept. 28 – despite the development of a moderate La Nina.
La Nina, a cooling of waters in the equatorial Pacific, usually is favorable for hurricanes.
What happened?
Bill Gray and Philip Klotzbach, the Colorado State University forecast team, believe that cooler waters in the tropical Atlantic were a factor. From April to September, they cooled about a degree Fahrenheit.
But why did that happen?
Amato Evan, a researcher at the University of Wisconsin, believes he has an answer: Dust.
As loyal readers might remember, powerful dust blowing up on the Sahara Desert create a “Saharan Air Layer” that covers the upper atmosphere all the way to the Caribbean.
Dust storm activity was minimal in August and September, says Amato, but during May, June and July it was the highest it has been in several years.
Amato’s hypothesis is that the all that dust blocked some of the sunlight and led to a cooling of the ocean surface.
Whatever the reasons, residents of the U.S. Gulf and Atlantic coasts undoubtedly are grateful, and U.S. taxpayers also should be grateful.
In 2005, the Federal Emergency Management Agency estimated that disaster expenditures for hurricanes, alone, totaled $38.7 billion.
This year, not a single disaster was declared for hurricanes.
Nationally, the most-expensive storm was Humberto, a category 1 storm with
h maximum winds of 90 m.p.h., which caused about $50 million in damages, according to the National Oceanic and Atmospheric Administration.
By contrast, Katrina, in 2005, caused over $100 billion in damages, by NOAA estimates.
In all, 14 named storms, those with winds of 39 m.p.h. or more, formed in the Atlantic Basin, which consists of the Gulf of Mexico, the Caribbean and the Atlantic.
September turned out to be one of the busiest hurricane months ever, and 2007 marked the first time that two Category 5 storms had made landfall in the same season.
That said, the overall, the season wasn’t as ferocious as forecasted, Gray and Klotzbach acknowledged.
Floridians wouldn’t mind a repeat next year, but Amato says that the dust may not be as plentiful.
Comments (1)
As a meteorologist in the US Navy I agree with Mr. Gray's conclusions. I have watched the SST all season and it has not been as warm as the previous season. Dust, which blocks incoming solar radiation (insolation) would indeed prevent the ocean water in the Caribbean from warming up. Dust over NW Africa also explains why the vast majority of tropical storms we did see this year (and several of which the NHC overforecasted) were in the Caribbean (Gulf of Mexico) and not the Atlantic.
Posted by Michael Kotyk | November 30, 2007 5:48 PM
Posted on November 30, 2007 17:48