s the 2007 Atlantic hurricane season officially comes to a close on November 30, NOAA scientists are carefully reviewing a set of dynamic weather patterns that yielded lower-than-expected hurricane activity across the Atlantic Basin. As a result, the United States was largely spared from significant landfalling storms. However, 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.
As a whole, 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 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, Ph.D., lead seasonal hurricane forecaster at NOAA's Climate Prediction Center. "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."
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). This limited Atlantic hurricane formation during that period. 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: Tropical Depression Barry came ashore near Tampa Bay, Fla., on June 2; Tropical Depression Erin hit southeast Texas on August 16 and 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 U.S. was reminded of the dangers of inland flooding. "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:
-- Eight storms formed in the Atlantic Basin during September - tying September 2002 for having the most storm formations during any given month.
-- For the first time in recorded history, two Category 5 hurricanes made landfall in the Atlantic Basin during the same season. Hurricane Dean hit the Yucatan Peninsula near Costa Maya on Aug. 21 with 165 mph winds, followed by Hurricane Felix on Sept. 2, near Punta Gorda, Nicaragua, with 160 mph winds.
-- With a central pressure of 906 millibars, Hurricane Dean had the third lowest pressure at landfall - behind the Labor Day 1935 Hurricane in the Florida Keys and Hurricane Gilbert of 1988 in Cancun, Mexico. Dean is also the first Category 5 hurricane to make landfall in the Atlantic Basin since Hurricane Andrew hit South Florida in 1992.
-- Hurricane Humberto grew from a tropical depression with top winds of 35 mph into a hurricane with winds of 85 mph within 24 hours - only three others storms (Celia 1970, Arlene and Flora 1963) intensified faster during a 24-hour period from below tropical storm strength.
-- NOAA's Climate Prediction Center will release an official summary of the 2007 Atlantic Hurricane Season in January 2008. NOAA will announce its 2008 hurricane outlooks for the Atlantic, East Pacific and Central Pacific in May.
NOAA's Atlantic and East Pacific hurricane outlooks are official products of its Climate Prediction Center in collaboration with scientists at the National Hurricane Center, Hurricane Research Division and the Hydrometeorological Prediction Center. NOAA's Central Pacific Outlook is an official product of the Central Pacific Hurricane Center in Honolulu, Hawaii, and in collaboration with the Climate Prediction Center.