**EL NIÑO/SOUTHERN OSCILLATION (ENSO)** **DIAGNOSTIC DISCUSSION**

**issued by**

**CLIMATE PREDICTION CENTER/NCEP/NWS**

**8 January 2009**

**[Synopsis:]{.underline} Developing La Niña conditions are likely to
continue into Northern Hemisphere Spring 2009.**

During December 2008, negative equatorial sea surface temperature (SST)
anomalies strengthened across the central and east-central Pacific Ocean
(Fig. 1). Correspondingly, the latest weekly SST index values were
−0.3°C in Niño-1+2, −0.9°C in Niño 3, −1.1°C in Niño 3.4, and −0.7°C in
Niño 4 (Fig. 2). The subsurface oceanic heat content anomalies (average
temperatures in the upper 300m of the ocean, Fig. 3) also became
increasingly negative as below-average temperatures at thermocline depth
strengthened in the central and eastern Pacific (Fig. 4). Convection
remained suppressed near the International Date Line, and became more
persistent near Indonesia during December. Low-level easterly winds and
upper-level westerly winds also strengthened across the equatorial
Pacific Ocean. Collectively, these oceanic and atmospheric anomalies
reflect the development of La Niña.

Nearly all of the recent forecasts for the Niño-3.4 region indicate a
continuation of below-average SSTs through the first half of 2009, with
at least one-half predicting La Niña conditions throughout the period
(Fig. 5). While the magnitude of cooling remains uncertain, NOAA's
official La Niña threshold (3-month average of the Niño-3.4 index less
than or equal to −0.5°C) is expected be met at least through
January-March 2009. Therefore, based on current observations, recent
trends, and model forecasts, La Niña conditions are likely to continue
into the Northern Hemisphere Spring 2009.

Despite the unusually late start to this La Niña, expected impacts
during January-March 2009 include above-average precipitation over
Indonesia and below-average precipitation over the central and eastern
equatorial Pacific. For the contiguous United States, potential impacts
include above-average precipitation in the Ohio and Tennessee Valleys
and below-average precipitation across the South, particularly in the
southwestern and southeastern states. Other potential impacts include
below-average temperatures in the Pacific Northwest and above-average
temperatures across much of the southern United States.

This discussion is a consolidated effort of the National Atmospheric and
Oceanic Administration (NOAA), NOAA's National Weather Service, and
their funded institutions. Oceanic and atmospheric conditions are
updated weekly on the Climate Prediction Center web site ([El Niño/La
Niña Current Conditions and Expert
Discussions](http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml)).
Forecasts for the evolution of El Niño/La Niña are updated monthly in
the [Forecast
Forum](http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/bulletin/forecast.shtml)
section of CPC\'s Climate Diagnostics Bulletin. The next ENSO
Diagnostics Discussion is scheduled for 5 February 2009. To receive an
e-mail notification when the monthly ENSO Diagnostic Discussions are
released, please send an e-mail message to:
<ncep.list.enso-update@noaa.gov>.

Climate Prediction Center\
National Centers for Environmental Prediction\
NOAA/National Weather Service\
Camp Springs, MD 20746-4304

![](media/image1.png){width="6.0in" height="3.3833333333333333in"}

Figure 1. Average sea surface temperature (SST) anomalies (°C) for the
four-week period 7 December 2008 - 3 January 2009. Anomalies are
computed with respect to the 1971-2000 base period weekly means (Xue et
al. 2003, *J. Climate*, **16**, 1601-1612).

![](media/image2.png){width="6.0in" height="6.816666666666666in"}

Figure 2. Time series of area-averaged sea surface temperature (SST)
anomalies (°C) in the Niño regions \[Niño-1+2 (0°-10°S, 90°W-80°W), Niño
3 (5°N-5°S, 150°W-90°W), Niño-3.4 (5°N-5°S, 170°W-120°W), Niño-4
(150ºW-160ºE and 5ºN-5ºS)\]. SST anomalies are departures from the
1971-2000 base period weekly means (Xue et al. 2003, *J. Climate*,
**16**, 1601-1612).

![](media/image3.png){width="6.0in" height="2.8666666666666667in"}

Figure 3. Area-averaged upper-ocean heat content anomalies (°C) in the
equatorial Pacific (5°N-5°S, 180º-100ºW). Heat content anomalies are
computed as departures from the 1982-2004 base period pentad means.

![](media/image4.png){width="6.0in" height="2.375in"}

Figure 4. Depth-longitude section of equatorial Pacific upper-ocean
(0-300m) temperature anomalies (°C) centered on the week of 29 December
2008. The anomalies are averaged between 5°N-5°S. Anomalies are
departures from the 1982-2004 base period pentad means.

![](media/image5.png){width="5.998611111111111in"
height="5.180555555555555in"}![](media/image6.wmf){width="1.0479166666666666in"
height="0.28055555555555556in"}

Figure 5. Forecasts of sea surface temperature (SST) anomalies for the
Niño 3.4 region (5°N-5°S, 120°W-170°W). Figure courtesy of the
International Research Institute (IRI) for Climate and Society. Figure
updated 17 December 2008.