Oceanic La Nina Fades to Neutral Phase

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Discussion: Last week, Nino34 SSTA warmed to -0.3C which is neutral ENSO (Fig. 1). Only the Nino4 region is at the La Nina threshold. The Nino3 SSTA warmed too exactly normal. The weekly observations maintain the trend of a slow decay of La Nina dating back to late last year. The La Nina signature remains evident near and east of the Dateline while the eastern equatorial Pacific is at normal, which represents a very weak La Nina Modoki signal (Fig. 2).

Subsurface temperature anomalies remain marginally cool near and east of the Dateline in the upper 60-65 meters of the ocean (Fig. 3). Off the northwest coast, the subsurface cooled last week. At deeper layers (below 100 feet), the ocean is warming although only to moderate levels. The West Pacific subsurface very warm SSTA has eased intensity slightly. In summary, marginal support to sustain La Nina remains intact.

The southern oscillation index (SOI) has bounced back into positive phase which indicates the climate pattern is La Nina-biased and able to create an increase in trade winds across the equatorial East Pacific Ocean. Consequently, despite the weakening oceanic La Nina, the climate pattern remains La Nina-biased.

The latest Nino34 SSTA forecast by all dynamic models indicate El Nino is likely by July with Australia Bureau of Meteorology indicating the strongest (El Nino) intensity (Fig. 4). Conversely, the Climate Impact Company projection for July is +0.5C which is a marginal and weak El Nino outlook.

In summary, La Nina climate persists although oceanic La Nina has weakened to neutral phase. El Nino is likely to form later in 2023 with July as a likely month of onset.

Fig. 1: The Nino SSTA regions and their 12-week observations.

Fig. 2: A weak La Nina Modoki has developed the past 2 weeks.

Fig. 3: Equatorial Pacific Ocean subsurface temperature anomalies.

Fig. 4: The Australia Burau of Meteorology collection of ENSO phase dynamic models and their forecast for July 2023.