From the Climate Prediction Center:
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. 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°C by the end of month. The weekly Niño-3.4 and Niño-4 regions remained greater than -0.5°C through May. The oceanic heat content (average temperature in the upper 300m of the ocean) was near average, but decreased slightly due to the emergence of below-average sub-surface temperatures in the eastern Pacific. 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. 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. A smaller number of models (mainly statistical) predict weak La Niña conditions (Niño-3.4 less than -0.5°C) 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).