La Niña conditions emerged in December 2024 and were reflected in below-average sea surface temperatures (SSTs) across the central and east-central equatorial Pacific Ocean [Fig. 1]. The latest weekly indices were -0.7°C in Niño-3.4 and -0.6°C in Niño-4, with values close to zero in Niño-1+2 and Niño-3 [Fig. 2]. Subsurface cooling in the equatorial Pacific Ocean strengthened significantly [Fig. 3], with below-average temperatures dominating the central and eastern equatorial Pacific Ocean [Fig. 4]. Low-level wind anomalies were easterly over the western and central Pacific, while upper-level wind anomalies were westerly over the central and eastern Pacific. Convection was suppressed over the Date Line and was enhanced over Indonesia [Fig. 5]. The traditional and equatorial Southern Oscillation indices were positive. Collectively, the coupled ocean-atmosphere system indicated La Niña conditions.

The dynamical models in the IRI plume continue to predict a weak La Niña during the winter seasons, as indicated by the Niño-3.4 index values less than -0.5°C [Fig. 6]. The North American Multi-Model Ensemble (NMME) predicts slightly cooler SST anomalies with La Niña persisting through February-April 2025. The forecast team favors the NMME guidance, predicting weak La Niña conditions through the early spring before transitioning to ENSO-neutral. Weak La Niña conditions are less likely to result in conventional winter/spring impacts, though predictable signals can still influence the forecast guidance (e.g., CPC's seasonal outlooks). In summary, La Niña conditions are present and are expected to persist through February-April 2025 (59% chance), with a transition to ENSO-neutral likely during March-May 2025 (60% chance; [Fig. 7]).