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

Synopsis: ENSO-neutral is favored into the Northern Hemisphere summer 2013.

During February 2013, ENSO-neutral continued although SSTs remained below average across the eastern half of the equatorial Pacific Ocean (Fig. 1). The Niño 3.4 index remained near -0.5^oC, while the Niño 3 index became less negative as the month progressed (Fig. 2). The oceanic heat content (average temperature in the upper 300m of the ocean) similarly increased during the month (Fig. 3), largely due to the eastward push of above-average temperatures at depth (Fig. 4). The Madden-Julian Oscillation (MJO) again contributed to increased atmospheric variability over the tropical Pacific during February. Anomalous low-level winds were primarily easterly over the west-central equatorial Pacific, while upper-level winds remained near average, but with some intra-monthly variability. Over Indonesia, anomalous convection remained enhanced north of the equator and suppressed south of the equator (Fig. 5). Due to the lack of persistent atmosphere-ocean coupling, the tropical Pacific continues to reflect ENSO-neutral.

Most models forecast Niño-3.4 SSTs to remain between 0^oC and -0.5^oC through Northern Hemisphere spring and to remain ENSO-neutral (between -0.5^oC and +0.5^oC) into the fall (Fig. 6). However, there is increasing model spread and overall less confidence in the forecast during the last half of the year, partly because of the so-called "spring barrier," which historically leads to lower model skill beginning in late spring. Thus, ENSO-neutral is favored into the Northern Hemisphere summer 2013 (see CPC/IRI consensus forecast).

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

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