As we noted on Friday, the 2007 hurricane season was remarkably kind to the United States (see Hurricane Season – Why So Quiet?).
Consider this fact: In fiscal 2005, the Federal Emergency Management Agency committed $37.6 billion for hurricane-related disasters. In fiscal 2007, not a single hurricane led to a disaster declaration, according to FEMA.
That is a stunning development given that the forecasts by both Colorado State University and the National Oceanic Atmospheric Administration were menacing.
The meteorologists, however, acknowledge that their outlooks were off the mark in the key areas of intensity and duration of storms, and now they’re trying to figure out why.
Gerry Bell, one of the NOAA forecasters, said the outcome was particularly perplexing given the alignment of La Nina, a generally active hurricane era and warm waters in the western Atlantic.
La Nina, a cooling of water in the equatorial Pacific, usually coincides with busy seasons, especially during those 25- to 40-year cycles of enhanced hurricane activity, such as the one we are in now.
Bell believes the big factor was increased vertical wind shear that snuffed out potential monster hurricanes before they had a chance to grow.
He and his colleagues are trying to figure out why, but he suspects it has something to do with heavy rains in Southeast Asia.
In all, 14 named named storms – those with winds of 39 m.p.h. or better – formed in the Atlantic Basin, which is close to normal. But Bell said they kept popping up and coming apart.
Bill Gray and Philip Kotzbach, the Colorado state forecast team believe that cooler waters in the tropical Atlantic, perhaps the result of atmospheric dust from the Sahara Desert, was the culprit.
To recap, the season got off to a quick start, and became the only season in history with two landfalling Category 5 hurricanes – both with winds over 160 m.p.h. But the season mysteriously fizzled in late September.
In their post mortem, Gray and Klotzbach referred to work by Amato Evan, a researcher at the University of Wisconsin. Evan holds that Saharan dust was the key.
Powerful Saharan dust storms create a “Saharan Air Layer” that covers the upper atmosphere all the way to the Caribbean.
Amato says that while dust-storm activity was minimal in August and September, it was quite brisk in May, June and July.
Amato’s hypothesis is that the all that dust blocked some of the sunlight and led to a cooling of the ocean surface.
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