[Vision2020] La Nina Comes Again

[J Ford]

EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION

January 12, 2006

Synopsis:  Developing La Niña conditions are expected to continue during the 
next 3-6 months.

Equatorial SST anomalies greater than +0.5ºC were restricted to the region 
between Indonesia and 165ºE during December, while negative anomalies less 
than –0.5ºC were observed at most locations between the date line and the 
South American coast (Fig. 1). By the end of the month the SST departures 
were negative in all of the Niño regions (Fig. 2). During the last several 
months surface and subsurface temperature anomalies have decreased in the 
region between 180ºW and the South American coast (Fig. 3). During the same 
period persistent stronger-than-average low-level equatorial easterly winds 
were observed over the central Pacific.Since early November there has been a 
persistent pattern of enhanced tropical convection near 130ºE (Indonesia) 
and suppressed convection near the date line (180ºW). Collectively, the 
present oceanic and atmospheric anomalies are consistent with the 
development of La Niña conditions in the tropical Pacific.

Over the past several months most of the statistical and coupled model 
forecasts have trended towards cooler conditions in the tropical Pacific 
through mid-2006. The spread of the most recent statistical and coupled 
model forecasts (weak La Niña to ENSO-neutral) indicates some uncertainty in 
the outlooks (Fig. 4). However, current conditions (stronger-than-average 
easterly winds over the central equatorial Pacific) and recent cooling 
trends in observed oceanic conditions support the continuation of La Nina 
conditions in the tropical Pacific during the next 3-6 months.

Based on current conditions in the tropical Pacific, the most recent SST 
predictions,and on results from historical studies on the effects of cold 
episodes, we expect wetter-than-normal (drier-than-normal) conditions to 
prevail over Indonesia (central equatorial Pacific) during the remainder of 
the NH winter. That pattern of tropical precipitation favors a northward 
shift in the position of the jet stream over the eastern North Pacific 
during winter, which is usually accompanied by drier-than-normal conditions 
over southern California and Arizona. However, given the late onset of La 
Niña there is considerable uncertainty as to whether or not typical La Niña 
impacts will be experienced in the West during the remainder of NH winter.

This discussion is a consolidated effort of NOAA and its funded 
institutions. Weekly updates for SST, 850-hPa wind, OLR and features of the 
equatorial subsurface thermal structure are available on the Climate 
Prediction Center web page at http://www.cpc.ncep.noaa.gov (Weekly Update). 
Forecasts for the evolution of El Niño/La Niña are updated monthly in the 
Forecast Forum section of CPC's Climate Diagnostics Bulletin. The next ENSO 
Diagnostics Discussion is scheduled for 9 February 2006. To receive an 
e-mail notification when the monthly ENSO Diagnostic Discussions are 
released, please send an e-mail message: ncep.list.enso-update at noaa.gov.

Climate Prediction Center
National Centers for Environmental Prediction
NOAA/National Weather Service

J  :]

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