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

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

During May 2013, ENSO-neutral continued, as reflected by the persistence of near-average sea surface temperatures (SSTs) across much of the equatorial Pacific Ocean (Fig. 1). However, below average SSTs in the eastern Pacific strengthened, with the weekly index values in the easternmost Niño-3 and Niño-1+2 regions near or less than -1.0^oC by the end of month (Fig. 2). The weekly Niño-3.4 and Niño-4 regions remained greater than -0.5^oC through May. The oceanic heat content (average temperature in the upper 300m of the ocean) was near average, but decreased slightly (Fig. 3) due to the emergence of below-average sub-surface temperatures in the eastern Pacific (Fig. 4). Across the Pacific, equatorial winds remained near average, except for weak low-level easterly anomalies in the western Pacific and weak upper-level westerly anomalies in the western and central Pacific. Tropical convection remained enhanced over Indonesia and suppressed over the central Pacific (Fig. 5). Despite a tendency toward cooler conditions, the overall state of the tropical Pacific was consistent with ENSO-neutral.

The majority of the model forecasts favor the continuation of ENSO-neutral, with most models predicting Niño-3.4 index values below zero (Fig. 6). A smaller number of models (mainly statistical) predict weak La Niña conditions (Niño-3.4 less than
-0.5^oC) as soon as the Northern Hemisphere summer. As a result, the forecast consensus indicates larger chances for La Niña relative to El Niño, but there still remains close to a 60% or greater chance of ENSO-neutral through 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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