Synopsis: ENSO-neutral conditions are expected to continue into Northern Hemisphere Fall 2008.
A transition from La Niña to ENSO-neutral conditions occurred during June 2008, as sea surface temperatures (SSTs) returned to near-average across the central and east-central equatorial Pacific Ocean (Fig. 1). Also, positive SST anomalies continued in the eastern equatorial Pacific. Consistent with this pattern, the latest weekly SST index was -0.1oC in the Niño-3.4 region, and +0.4oC in the Niño 1+2 region (Fig. 2). The subsurface oceanic heat content (average temperatures in the upper 300m of the ocean, Fig. 3) and patterns of subsurface temperature anomalies (Fig. 4) also reflected the transition to ENSO-neutral conditions. Positive heat content anomalies were associated with above-average temperatures at thermocline depth across the entire equatorial Pacific, while small negative subsurface temperature anomalies persisted near the Date Line between the surface and 75m depth.
Similar to past transitions, La Niña continues to linger in the atmospheric circulation, but with diminishing strength. Enhanced low-level easterly winds and upper-level westerly winds remain across the central equatorial Pacific, while convection continues to be suppressed in the central equatorial Pacific and slightly enhanced over the far western Pacific. Collectively, these atmospheric and oceanic anomalies are consistent with a return from La Niña to ENSO-neutral.
Most of the recent dynamical and statistical SST forecasts for the Niño 3.4 region indicate ENSO-neutral conditions (-0.5 to 0.5 in the Niño-3.4 region) will continue through Northern Hemisphere Winter 2008-09 (Fig. 5). Despite this model consensus, the possible development of El Niño or La Niña cannot be ruled out due to uncertainty in model forecasts and because ENSO events often form during the second half of the year. Based on current atmospheric and oceanic conditions, recent trends, and model forecasts, ENSO-neutral conditions are expected to continue into Northern Hemisphere Fall 2008.
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). 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 7 August 2008. To receive
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