September 10, 2010

NOAA: Expect More Hurricanes Due To La Nina

The active hurricane season could get even busier due to the strengthening of the La Nina climate system, the National Oceanic and Atmospheric Administration (NOAA) said in an update on Thursday.

The update comes as Texas residents are cleaning up from the flooding rains that swept through from Tropical Storm Hermine.

La Nina was reported to be developing a month ago and has strengthened throughout August. It appears likely to last through early 2011, NOAA's Climate Prediction Service said.

La Nina is marked by a cooling of the tropical Pacific Ocean. It can "contribute to increased Atlantic hurricane activity by decreasing the vertical wind shear over the Caribbean Sea and tropical Atlantic Ocean," the center said.

Wind shear is a sharp difference in wind speed at different altitudes in the atmosphere. A strong wind shear reduces hurricanes by breaking up their ability to rise into the air, while less shear lets hurricanes strengthen and climb.

The NOAA forecast in August for 14 to 20 named tropical systems. The hurricane season began June 1 and ends November 30, with the peak period running from August to October.

La Nina phenomenon can impact climate worldwide by changing the direction and strength of winds and altering air pressure and rainfall patterns. In addition to hurricanes in the Atlantic, the impact of La Nina can include above-average rain or snowfall in the Pacific Northwest and below-average precipitation in the Southwest and parts of the Mississippi and Tennessee Valleys.

NOAA said its climate models disagree on how strong La Nina will be, but all concur it will last at least through early 2011.


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