ENSO-neutral continued during August 2024, with near-average sea surface temperatures (SSTs) observed across most of the equatorial Pacific Ocean [Fig. 1]. The weekly Niño indices did not change substantially during the month, with the latest weekly index values varying between +0.2°C (Niño-4) and -0.4°C (Niño-1+2; [Fig. 2]). Below-average subsurface temperatures were also similar to those in early August (area-averaged index in [Fig. 3]). Negative temperature anomalies continued to dominate across most of the subsurface equatorial Pacific Ocean [Fig. 4]. Low-level wind anomalies were easterly over most of the equatorial Pacific, and upper-level wind anomalies were easterly over the east-central Pacific. Convection was slightly enhanced over parts of Indonesia and was near average near the Date Line [Fig. 5]. Both the Southern Oscillation index and the 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]. This month, the team relies more on the latest North American Multi-Model Ensemble (NMME) guidance, which predicts La Niña to emerge in the next couple of months and continue through the Northern Hemisphere winter. The continuation of negative subsurface temperatures and enhanced low-level easterly wind anomalies supports the formation of a weak La Niña. A weaker La Niña implies that it 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 favored to emerge in September-November (71% chance) and is expected to persist through January-March 2025 [Fig. 7].