La Nina 2017-18 remains biased cool across the eastern half of the equatorial Pacific Ocean to the east of the Dateline. The Nino4 sea surface temperature anomaly (SSTA) region which represents equatorial SSTA near and just east of the Dateline remains in neutral ENSO phase (Fig. 1). The Nino34 SSTA is within moderate La Nina criteria while off the northwest coast of South America La Nina is quite strong (Nino3/Nino12).
Fig. 1: The 12-week Nino SSTA observations indicate a transition to La Nina except near the Dateline (Nino4) where SSTA is neutral.
Fig. 2: Weekly NCEP/CPC Pacific SSTA analysis identifies the state of the current La Nina pattern.
Fig. 3-4: Subsurface equatorial Pacific Ocean water temperature anomalies from Nov. 20 and Dec. 19.
The weekly SSTA analysis issued by NOAA identifies the cool bias of cold ENSO in the far eastern equatorial Pacific (Fig. 2). The subsurface trend in the equatorial East Pacific over the past one month indicates strong cool anomalies are present off the northwest coast of South America while warmer waters are evolving near the Dateline (Fig. 3-4).
The cool water supply to sustain La Nina remains in-place. However, the peak (cool water) supply has likely passed peak (Fig. 5).
Fig. 5: Upper ocean heat analysis in the equatorial East Pacific.
ENSO forecasts generally agree that La Nina will continue through northern hemisphere winter and weaken to neutral phase during next spring (Fig. 6). Forecast models trend toward El Nino later in 2018.
Fig. 6: A collection of dynamic and statistical ENSO phase forecast models done by the International Research Institute.