On the heels of El Niño, its opposite, La Niña may soon arrive. In a weekly update, scientists at the NOAA Climate Prediction Center noted that as the 2006-2007 El Niño faded, surface and subsurface ocean temperatures have rapidly decreased. Recently, cooler-than-normal water temperatures have developed at the surface in the east-central equatorial Pacific, indicating a possible transition to La Niña conditions.
Typically, during the U.S. spring and summer months, La Niña conditions do not significantly impact overall inland temperature and precipitation patterns, however, La Niña episodes often do have an effect on Atlantic and Pacific hurricane activity.
“Although other scientific factors affect the frequency of hurricanes, there tends to be a greater-than-normal number of Atlantic hurricanes and fewer-than-normal number of eastern Pacific hurricanes during La Niña events,” said retired Navy Vice Adm. Conrad C. Lautenbacher, Ph.D., under secretary of commerce for oceans and atmosphere and NOAA administrator. “During the winter, usual La Niña impacts include drier and warmer-than-average conditions over the southern United States."
“NOAA's ability to detect and monitor the formation, duration and strength of El Niño and La Niña events is enhanced by continuous improvements in satellite and buoy observations in the equatorial Pacific,” Lautenbacher added. “These observing systems include the TAO/TRITON moored and Argo drift buoys, as well as NOAA's polar orbiting satellites.”
La Niña conditions occur when ocean surface temperatures in the central and east-central equatorial Pacific become cooler than normal. These changes affect tropical rainfall patterns and atmospheric winds over the Pacific Ocean, which influence the patterns of rainfall and temperatures in many areas worldwide.
“La Niña events sometimes follow on the heels of El Niño conditions,” said Vernon Kousky, research meteorologist at the NOAA Climate Prediction Center. “It is a naturally occurring phenomenon that can last up to three years. La Niña episodes tend to develop during March-June, reach peak intensity during December-February, and then weaken during the following March-May.
“The last lengthy La Niña event was 1998-2001, which contributed to serious drought conditions in many sections of the western United States,” said Douglas Lecomte, drought specialist at the NOAA Climate Prediction Center.
NOAA will issue the U.S. Spring Outlook on March 15, and its Atlantic Hurricane Season Outlook in May. Both outlooks will reflect the most current La Niña forecast.
“While the status of El Niño/La Niña is of vital importance to our seasonal forecasts, it is but one measure we use when making actual temperature and precipitation forecasts,” said Kousky.
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