The 2007 Atlantic Basin hurricane season officially came to a close on Friday, but scientists with the National Oceanic and Atmospheric Administration (NOAA) are reviewing a set of dynamic weather patterns to understand why there was lower-than-expected hurricane activity across the region.
The United States was "largely spared" from significant landfalling storms, but "several noteworthy events took place, including two back-to-back Category 5 hurricanes hitting Central America and the rapid near-shore intensification of the single U.S. landfalling hurricane," NOAA noted.
"The 2007 Atlantic hurricane season produced the predicted number of named storms, but the combined number, duration and intensity of the hurricanes did not meet expectations," said Gerry Bell, lead seasonal hurricane forecaster for NOAA's Climate Prediction Center (CPC). "The United States was fortunate this year to have fewer strong hurricanes develop than predicted. Normally, the climate patterns that were in place produce an active, volatile hurricane season."
Overall, the 2007 Atlantic hurricane season produced a total of 14 named storms, including six hurricanes, two of which became major hurricanes. NOAA's August update to the seasonal forecast predicted 13 to 16 named storms -- of which seven to nine would be hurricanes, including three to five major hurricanes of Category 3 strength or higher. An average season has 11 named storms, with six becoming hurricanes, including two major hurricanes.
The climate patterns predicted for the 2007 hurricane season -- an ongoing multi-decadal signal (the set of oceanic and atmospheric conditions that have spawned increased Atlantic hurricane activity since 1995) and La Nina -- produced the expected below-normal hurricane activity over the eastern and central Pacific regions. However, La Nina's impact over the Atlantic was weaker than expected, which resulted in stronger upper-level winds and increased wind shear over the Caribbean Sea during the peak months of the season (August-October).
La Nina's effects appeared to limit Atlantic hurricane formation during that period, and now NOAA's scientists are investigating possible climate factors that may have led to this lower-than-expected activity.
All in all, one hurricane, one tropical storm and three tropical depressions struck the United States during the season: Tropical Depression Barry came ashore near Tampa Bay, FL, on June 2; Tropical Depression Erin hit southeast Texas on Aug. 16; Tropical Depression Ten came ashore along the western Florida panhandle on Sept. 21; Tropical Storm Gabrielle hit east-central North Carolina on Sept. 9, and Hurricane Humberto hit the upper Texas coast on Sept. 13.
Also this year, the United States was reminded of the dangers of inland flooding, NOAA noted. "Texas and Oklahoma experienced deadly flooding when Erin dumped up to 11 inches of rain. Fresh water flooding is yet another deadly aspect of tropical cyclones," said Ed Rappaport, acting director of NOAA's National Hurricane Center.
Other noteworthy statistics of the season include:
The CPC will release an official summary of the 2007 Atlantic Hurricane Season in January, and NOAA will announce its 2008 hurricane outlooks for the Atlantic, East Pacific and Central Pacific in May.
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