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Mature phase of La Nina continues. ENSO maintains a cool La Nina signature in the eastern equatorial Pacific while toward the Dateline SSTA is near normal (Fig. 1-2).  Not typical of cold ENSO is the anomalous warmth in the subtropics of the central and east North and South Pacific and a likely cause of La Nina 2017-18 weakness. The subsurface remains cool in the eastern equatorial Pacific sustaining the La Nina event while anomalous warmth east of the Dateline and at depth is eroding that cool support (Fig. 3). The ECMWF Nino34 SSTA forecast indicates La Nina ends in April with a trend toward El Nino later this year (Fig. 4). The historical precedent of ENSO for 2018 mid-to-late year on global climate is most likely a weak La Nina to weak El Nino transition.

Fig. 1: The 12-week Nino SSTA observations indicate a steady La Nina episode although toward the Dateline (Nino4) temperatures are neutral.  

Fig. 2: Weekly POAMA Pacific SSTA analysis identifies a weak La Nina pattern.  The warm zones in the subtropics have hurt La Nina from being stronger.

Fig. 3: Subsurface equatorial Pacific Ocean water temperature anomalies from Jan. 8 indicate La Nina-sustaining cool waters in the East Pacific being eroded from the west.

Fig. 4: ECMWF Nino34 SSTA forecast indicates La Nina is finished in April and El Nino is possible later in 2018.