El Niño continued during March but continues to weaken. 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 March was +1.24˚C, remaining within the El Niño range. Oceanic El Niño has weakened by about 0.55˚C since January.
The Southern Oscillation Index (SOI) was in the neutral range during March (+0.1) and January-March (-0.2).
Trade wind strength was well above normal near and west of the International Date Line during March. This generated an upwelling Kelvin Wave in the west-central equatorial Pacific, which should see cooler than average sub-surface ocean water move across the Pacific over the next two months.
Enhanced trade winds are forecast to continue near the International Date Line during April, which should result in additional oceanic cooling.
At the end of March, the subsurface equatorial Pacific was cooler than average across most of the basin below 100 m depth, with below average temperatures moving closer to the surface in the east during March. Notably, subsurface waters were 3˚C to 5˚C below average in the east, lending credence to the eventual development of La Niña later this year.
During March, convective forcing favoured the western Pacific with subsidence over the eastern Pacific and South America, a La Niña-like pattern. This was linked to a strong, early-month pulse of the Madden-Julian Oscillation (MJO) as well as a South Pacific Convergence Zone that was displaced well south-west of its climatological position. This delivered excessive rainfall to Vanuatu, Fiji, and parts of Tonga during the month. By late March, the pulse had propagated into the eastern Pacific, generating an El Niño-like response. Such variability is to be expected from an ocean-atmosphere system that is transitioning toward an ENSO-neutral state.
The tropical cyclone season continues through April. Activity looks unlikely through the first half of the month.
