Oct. 6 (Bloomberg) -- La Nina, a cooling of the Pacific Ocean that can affect weather around the world, is expected to strengthen gradually into 2012, according to the U.S. Climate Prediction Center.
Cool spots in the eastern Pacific Ocean are about 0.5 degrees Celsius (0.9 degrees Fahrenheit) below average, the center said in a report today.
“La Nina is not as strong as it was in September 2010,” the center said. “Roughly one-half of the models predict La Nina to strengthen during the Northern Hemisphere fall and winter.”
On average, La Ninas occur every three to five years and last from nine to 12 months. They sometimes occur in back-to- back years, as is happening now. Last year’s La Nina was a contributor to record flooding in Australia and in the U.S., the persistent Texas drought and an above-average Atlantic hurricane season, according to Australia’s Bureau of Meteorology and agencies of the U.S. National Oceanographic and Atmospheric Administration.
La Nina cuts down on wind shear in the Atlantic, which can inhibit hurricane formation, according to NOAA.
When La Ninas come in back-to-back years, the second has been weaker than the first in the three of the five such occurrences since 1950, the climate center said. This year, the National Centers for Environmental Prediction’s forecast says the current La Nina may become as strong as last year’s.
La Nina’s impact in the U.S. will probably be weak through November and increase in mid-December, the climate center said. That may mean drought conditions in the South will continue.
The phenomenon tends to shift the storm track across the U.S. farther to the north, which means less rain for Texas and other southern states.
This past year, in combination with a shift in pressure over the North Pole known as the Arctic Oscillation, more snow fell across the upper Great Plains. When the snow melted during the spring, it caused record flooding along the Ohio, Mississippi and Missouri rivers as far south as Louisiana.
--Editors: Charlotte Porter, Richard Stubbe
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