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.
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