Oceanic and atmospheric conditions in the Pacific basin continued to
reflect the neutral phase of the ENSO cycle during June 2004. Sea surface
temperatures were warmer-than-average in the western equatorial Pacific (Niņo
4 region), near average in the central equatorial Pacific (Niņo 3.4 and
Niņo 3 regions) and cooler-than-average in the eastern equatorial Pacific (Niņo
1+2 region) during the month (Fig. 1). Positive SST anomalies greater than +0.5°C (~1°F) were found between
160°E and 150°W, while negative SST anomalies less than -0.5°C were found
between 95°W and the South American coast (Fig. 2).
During the past several months, positive SST anomalies have persisted in
the west-central equatorial Pacific (150°E-160°W), low-level easterly wind
anomalies (enhanced east-to-west flow) have been observed over the central
equatorial Pacific, and low-level westerly anomalies have persisted over the
western equatorial Pacific (Fig. 3, top). These features have favored
persistent enhanced tropical convection (negative OLR anomalies) in the
region 140°E-180°W (Fig. 3, bottom). The low-level easterly wind anomalies
over the central equatorial Pacific have also contributed to a
steeper-than-average thermocline slope in the upper ocean, which is
reflected in the pattern of subsurface temperature anomalies [positive
(negative) in the central-western (eastern) equatorial Pacific] (Fig.
4).
Both the surface and subsurface temperature fields showed trends toward
near-average conditions (decreased magnitude of the anomalies) during June.
Considerable intraseasonal variability (MJO activity) in recent months
has resulted in week-to-week and month-to-month variability in many
atmospheric and oceanic indices. During mid-June through early July the
easterlies weakened in many areas of the equatorial Pacific, as enhanced
convection shifted eastward from the Indian Ocean to the western tropical
Pacific. The greatest wind and convection anomalies occurred north of the
equator in the western Pacific, associated with two typhoons. It is too
early to determine whether this event will have any significant impact on
the thermal structure of the equatorial Pacific Ocean.
Slightly more than half of the statistical and coupled model forecasts
indicate near neutral conditions in the tropical Pacific (Niņo 3.4 SST
anomalies between -0.5°C and +0.5°C) through the northern summer and fall
2004. The remaining forecasts indicate borderline El Niņo conditions (Niņo
3.4 SST anomalies slightly greater than +0.5°C) will develop within the
next 3-6 months. Given the recent trends and observed oceanic and
atmospheric patterns discussed above, ENSO-neutral conditions are expected
to continue for the next 3 months (through September 2004).
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. To receive
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