July 30, 2009

With less than one week left in July, no hurricane has formed in the Atlantic Ocean.  Meteorologists at the University of Kentucky College of Agriculture largely attribute this anomaly to El Niño, which  also may be the reason July 2009 will be one of the coolest Julys in the past 100 years.

"The Climate Prediction Center defines El Niño as a period of exceptionally warm sea- surface temperatures across the eastern tropical Pacific, where the one-month mean temperature anomaly in that area warms above 0.5 degrees Celsius and persists for three months," said Keys Arnold, UK agricultural meteorologist. "El Niño patterns typically develop every three to seven years during the period of June to August and reach peak strength during the subsequent winter months."

Typical impacts of El Niño in the Bluegrass State during the winter months include mild and dry conditions.

UK Agricultural Meteorologist Tom Priddy said one of the primary impacts of El Niño during the warm season is a suppression of hurricane formation in the Atlantic Ocean. 

"When El Niño conditions are present, an unusually high amount of wind shear is present over the Atlantic Ocean," he said. "Wind shear, the changing of wind speed and direction with height, is a major deterrent of hurricane formation, as it hinders the development and strengthening of tropical storm systems."

Arnold said the last time the first hurricane developed this late in the season was 2004, when El Niño conditions also were present.

Even though the Bluegrass State does not lie along the Atlantic or Gulf coasts, Arnold said the impacts of hurricanes have recently been felt here.  In September of 2008 in western portions of the state, remnants of Hurricane Ike caused hurricane force wind gusts of more than 74 mph  and sustained wind speeds of more than 50 mph.  Numerous power outages were reported. 

In 2007, remnants of several hurricanes positively affected the state by providing copious amounts of rainfall during a time in which much of the state was in severe and extreme drought. 

"Since El Niño began to develop in the late spring and continued to strengthen during the early summer, Kentucky has not needed the additional rainfall from tropical remnants, as an active weather pattern has been in place across the eastern United States," Priddy said.  "Drought conditions have not been a concern here this growing season, which has seen above-normal rainfall during ten of the past 13 weeks." 

As El Niño conditions began to develop, a change in the temperature pattern also took place. 

"While the Commonwealth experienced above-normal temperatures during the past five months, significantly below-normal values have been reported every week thus far in July," Arnold said.  "In fact, when it's all said and done, Kentucky may experience one of the coolest Julys in the past 100 years."                 

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