Over the past month, ENSO-neutral continued, as evidenced by overall near-average sea surface temperatures (SSTs) observed across the central and eastern equatorial Pacific Ocean [Fig. 1]. Similar to last month, the latest weekly Niño indices ranged from +0.2°C (Niño-4) to -0.3°C (Niño-3.4; [Fig. 2]). Below-average subsurface temperatures persisted [Fig. 3] across the east-central and eastern equatorial Pacific Ocean [Fig. 4]. For the monthly average, low-level wind anomalies were easterly over a small region of the east-central equatorial Pacific, and upper-level wind anomalies were near average. Convection was suppressed over the Date Line and was weakly enhanced over eastern Indonesia [Fig. 5]. The traditional and equatorial Southern Oscillation indices were positive. Collectively, the coupled ocean-atmosphere system reflected ENSO-neutral.

The IRI plume predicts a weak and a short duration La Niña, as indicated by the Niño-3.4 index values less than -0.5°C [Fig. 6]. The latest North American Multi-Model Ensemble (NMME) forecasts are cooler than the IRI plume and predict a weak La Niña. Due to this guidance and La Niña-like atmospheric circulation anomalies over the tropics, the team still favors onset of La Niña, but it is likely to remain weak and have shorter duration than other historical episodes. A weak La Niña would be less likely to result in conventional winter impacts, though predictable signals could still influence the forecast guidance (e.g., CPC's seasonal outlooks). In summary, La Niña is most likely to emerge in October-December 2024 (57% chance) and is expected to persist through January-March 2025 [Fig. 7].