[californiadisasters] El Nino/La Nina Diagnostic Discussion (February 2013)

Synopsis: ENSO-neutral is favored through Northern Hemisphere spring 2013.

During January 2013, ENSO-neutral continued, although below-average sea surface temperatures (SST) prevailed across the eastern half of the equatorial Pacific (Fig. 1). While remaining below average, a high degree of variability in the weekly Niño 3 and 3.4 indices was apparent during the month (Fig. 2). The oceanic heat content (average temperature in the upper 300m of the ocean) was also below-average (Fig. 3), largely reflecting negative subsurface temperature anomalies in the eastern Pacific. At the same time, positive anomalies increased and expanded eastward to the central Pacific by late January (Fig. 4). The variability in both the ocean and atmosphere was enhanced during January, at least partially due to a strong Madden-Julian Oscillation (MJO). Consequently, the location of the MJO was reflected in the monthly averages of wind and convection. Anomalous upper-level winds were westerly over the eastern half of the equatorial Pacific, while low-level winds were near average. Relative to December 2012, the region of enhanced convection shifted eastward and became more prominent over Indonesia and the western equatorial Pacific (Fig. 5). Despite these transient features contributing to cool conditions, the collective atmospheric and oceanic system reflects ENSO-neutral.

The vast majority of models predict near-average SST (between -0.5^oC and +0.5^oC) in the Niño-3.4 region through the late Northern Hemisphere summer (Fig. 6). However, because model skill is generally low during April-June, there is less confidence in the forecast beyond the spring. Thus, ENSO-neutral is favored through Northern Hemisphere spring 2013 (see CPC/IRI consensus forecast).

Source: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

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