Tropical Pacific conditions are in the neutral range, after the end of the 2011/12 La Niña event. The SOI is now significantly negative (below –0.5 standard deviations) for (almost) the first time in two years.
The three–month mean SOI (FMA) is near zero. Zonal wind anomalies were mostly positive across the equatorial Pacific in April, but strengthened trade winds were evident over the western Pacific toward the end of the month. The OLR anomaly field is losing its large–scale signature and no longer reflects a La Niña pattern.
The TRMM ENSO index has eased considerably to –0.2 for the 30 days to 25 April. SSTs are close to normal across much of the equatorial Pacific but are above normal near the South American coast. In April, NINO3.4 was around –0.3°C (FMA mean 0.5°C): NINO3 is now +0.4°C while NINO4 remains negative at –0.3°C (FMA means +0.2°C and –0.6°C, respectively).
At the sub–surface, the positive heat content anomaly in the western Pacific continues to propagate eastwards after a pause in March, while the negative anomaly in the east has all but disappeared. After significant activity in March, the MJO has been weak in April, and is expected to remain so going in to May. Convection is presently enhanced in the SPCZ, which is lying near its normal position.
Eight of the ten dynamical models and all the statistical models NIWA monitor predict ENSO–neutral conditions for early winter (MJJ), with two dynamical models projecting El Niño conditions. Six of the dynamical models indicate development (or continuation) of El Niño conditions during ASO.
The latest IRI technical summary of 19 April indicates around a 90% chance of neutral conditions for April–June (and ~10% chance of La Niña).
For JAS, El Niño conditions are given a likelihood of around 45%, with neutral conditions at 55%
