El Niño continued to weaken during April, and ENSO neutral conditions are favoured to develop by June 2024.
The monthly NINO3.4 Index anomaly (in the central equatorial Pacific) at the end of April was +0.82˚C, remaining just above the El Niño threshold of +0.7˚C.
The Southern Oscillation Index (SOI) was in the neutral range during April (-0.2) and February-April (-0.4).
Trade wind strength was above normal near the equator in the eastern and western Pacific, but near normal in the central part of the basin. This was associated with additional cooling of the surface ocean water across the equatorial Pacific.
Periods of enhanced trade winds throughout May which should contribute to additional cooling near the equator.
At the end of April, the subsurface equatorial Pacific was 4˚C to 6˚C cooler than average just below the surface in the east of the basin.
Meanwhile, above average temperatures persisted in the central part of the basin. This signature was reflective of an oceanic transition out of El Niño toward a possible La Niña in a few months.
During April, convective forcing favoured the western Indian Ocean and Africa. In the Pacific, anomalous rising motion in the central tropical Pacific was the result of an early-month pulse of the Madden-Julian Oscillation (MJO). Sinking air was dominant over the eastern tropical Pacific, consistent with cooling seas there.
The South Pacific Convergence Zone was near its climatological normal position during April.
As the ocean-atmosphere system transitions to ENSO neutral, higher frequency variability (e.g., from the MJO) is likely to be more dominant, which may encourage more variable weather patterns in the months ahead.
