warm-episode (El Niņo) conditions are expected to continue
for the next three months.
sea surface temperature (SST) anomalies greater than +0.5°C (~1°F) persisted across most of
the central and western equatorial Pacific during December 2004 (Fig.
the end of the month, positive equatorial SST anomalies greater than
+1°C (~2°F) were found from 160°E eastward
to 155°W and locally in the region near 110°W (Fig.
2). During December
SST anomalies exceeded 0.5°C in the Niņo 4, Niņo 3.4 and Niņo
3 regions, while anomalies remained near zero along the West Coast of South
America (Niņo 1+2 region) (Fig. 3). The
pattern of anomalous warmth in the equatorial Pacific in recent months and
the most recent 5-month running mean value of the Southern Oscillation Index
(-0.6) indicate that a weak warm (mid-Pacific El
Niņo) episode has developed.
However, through December there has been a lack of persistent enhanced
convection over the anomalously warm waters of the central equatorial
Pacific (Fig. 4), which has limited El Niņo-related impacts on the
global pattern of precipitation. (Note: The recent pattern of heavy precipitation in California has been associated with 1) a
persistent high-latitude blocking ridge in the vicinity of the Gulf of
Alaska and an associated trough along the West Coast, and 2) a weaker than
average jetstream across the central and eastern Pacific. These circulation
features are not consistent with El Niņo,
which would favor a stronger-than-average jetstream over the central and
eastern Pacific and a reduced tendency for blocking in the
Gulf of Alaska.
Since late 2003 MJO activity has resulted in
week-to-week and month-to-month variability in many atmospheric and oceanic
indices. The MJO activity weakened considerably during early November 2004
and remained weak through mid-December. However, during the last half of
December the MJO strengthened, as enhanced convection and precipitation over
the Indian Ocean shifted eastward across Indonesia (Fig.
5). By early January 2005, enhanced convection extended into the
western tropical Pacific. The Climate Prediction Center
will continue to closely monitor the evolution of this activity over the
next several weeks as it shifts eastward over the abnormally warm waters in
the central equatorial Pacific.
Based on the recent evolution of
oceanic and atmospheric conditions and on a majority of the statistical and
coupled model forecasts, it seems most likely that weak warm episode (El Niņo)
conditions will persist for at least the next three months. However,
there is considerable uncertainty concerning future developments in the
extreme eastern equatorial Pacific (the classical El Niņo
impacts include drier-than-average conditions over portions of
(through early 2005), northern and northeastern
(through February 2005), and southeastern
(through March 2005). If the warming in the tropical Pacific strengthens and
spreads eastward to the South American coast, then wetter-than-average
conditions would be expected in coastal sections of
during March-April 2005, and drier-than-average conditions would be expected
to develop in
during February through April 2005. Expected US
impacts during Northern Hemisphere winter include warmer-
conditions in the West and in the northern Plains, and cooler- and
wetter-than-average conditions for portions of the South and Southeast.
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 Niņo/La Niņa are updated monthly in the Forecast Forum
section of CPC's Climate Diagnostics Bulletin. The
next ENSO Diagnostics Discussion is scheduled for 10 February 2005. To receive
an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send
your e-mail address to: email@example.com.