El Niño expected for Northern Hemisphere: NOAA

NOAA – A transition from ENSO-neutral is expected in the next couple of months, with a greater than 90 per cent chance of El Niño persisting into the Northern Hemisphere winter.

During April, above-average sea surface temperatures (SSTs) expanded slightly westward to the east-central equatorial Pacific Ocean. The latest weekly Niño-3.4 index value was +0.4 degrees Celsius, with the easternmost Niño-3 and Niño1+2 regions at +0.8°C and +2.7°C, respectively. Area-averaged subsurface temperature anomalies continued to increase, reflecting widespread positive temperature anomalies below the surface of the equatorial Pacific Ocean. Low-level wind anomalies were westerly during mid-April before switching back to easterly by the end of the month. Upper-level wind anomalies were westerly across most of the Pacific Ocean. Suppressed convection was observed over parts of Indonesia and anomalies weakened near the Date Line. While the warming near coastal South America continued to be striking, the basin-wide coupled ocean-atmosphere system remained consistent with ENSO-neutral.

The most recent plume from the International Research Institute for Climate and Society at Columbia University also indicates El Niño is likely to form during the May to July season and persist into the winter. The combination of a forecasted third westerly wind event in mid-late May, and high levels of above-average oceanic heat content, means that a potentially significant El Niño is on the horizon. While at least a weak El Niño is likely, the range of possibilities at the end of the year (November to January) include an 80 per cent chance of at least a moderate El Niño (Niño-3.4 ≥ 1.0°C) to an approximately 55 per cent chance of a strong El Niño (Niño-3.4 ≥ 1.5°C). It is still possible the tropical atmosphere does not couple with the ocean, and El Niño fails to materialize (five to 10 per cent chance).

In summary, a transition from an El Nino/Southern Oscillation (ENSO) is expected in the next couple of months, with a greater than 90 per cent chance of El Niño persisting into the Northern Hemisphere winter.