Latest WMO ENSO Update on 8 September 2014

Current Situation and Outlook 

Despite warming of the Tropical Pacific Ocean up until June, the overlaying atmosphere largely failed to respond. As a result, ocean temperature anomalies along the equator have decreased over the past two months. Changes in the wind patterns in early-August brought some weak re-warming, but winds have now returned to near normal in the western Pacific, while the pattern of cloudiness has remained largely neutral. Despite the recent observations, models and expert opinion suggest that the development of a weak El Niño event in the coming several months remains quite possible, with probability of at least 60%. National Meteorological and Hydrological Services and other agencies will continue to monitor Pacific Ocean conditions for further El Niño developments, and will assess the most likely local impacts.

August 2014 was the second month in a row that sea surface temperatures across much of the central and east-central tropical Pacific Ocean approached near normal conditions, after peaking at more than 0.5 degrees Celsius above normal during May and June. Despite the earlier oceanic warming, most atmospheric indicators (e.g., sea level pressure, cloudiness and trade winds) have remained near neutral levels, indicating that El Niño conditions had not become established. Notably, the heat below the surface of the tropical Pacific, which had been very much above average from March to May, returned to near- average levels during July and August. Additionally, the expected west-to-east difference in sea surface temperature anomaly has not appeared, with sea surface temperatures in the western tropical Pacific remaining above average. It is noted that while the basin-wide condition has behaved as described, the sea surface temperatures over the far eastern tropical Pacific have remained well above average since April.

However, the latest outlooks from climate models and expert opinion suggest that central tropical Pacific Ocean surface temperatures may warm again, potentially approaching El Niño levels during the coming three months. Atmospheric patterns associated with El Niño may accompany the warmed sea surface temperatures. The seasonal southward migration of the Intertropical Convergence Zone towards the equator may allow any further increases in sea surface temperatures to more easily increase cloudiness and rainfall in the central tropical Pacific, making ocean-atmospheric coupling more likely than in recent months.

International climate model outlooks collectively suggest 55% to 60% likelihood for El Niño to become established between September and November, rising as high as 70% for the November to February period. Although there remains a range of possibilities for the strength of the likely El Niño, a weak event appears likely, though a moderate strength event cannot be discounted. A strong event appears most unlikely. The earlier that a coupling of any oceanic warming in the central tropical Pacific and the atmospheric patterns of weakened trade winds and cloudiness emerge, the greater the likelihood that the likely El Niño event will form and grow during the final months of 2014.

It is important to note that El Niño and La Niña are not the only factors that drive global climate patterns. At the regional level, seasonal outlooks need to assess the relative impacts of both the El Niño/La Niña state and other locally relevant climate drivers. For example, the state of the Indian Ocean Dipole, or the Tropical Atlantic SST Dipole, may impact the climate in the adjacent land areas. Locally applicable information is available via regional/national seasonal climate outlooks, such as those produced by WMO Regional Climate Centres (RCCs), Regional Climate Outlook Forums (RCOFs) and National Meteorological and Hydrological Services (NMHSs).

In summary:

  • Tropical Pacific Ocean surface temperature anomalies decreased during July and August after having reached around 0.5 degrees Celsius above normal in May and June. Atmospheric indicators have remained mainly neutral throughout the recent several months;
  • As of mid-August 2014, model outlooks suggested up to a 60% chance that oceanic warming would exceed El Niño thresholds during the September to November period, peaking during the final months of 2014 and lasting into early 2015;
  • Although a range of strength outcomes are possible, models surveyed and expert opinion favour a weak event, although a moderate strength event remains possible. A strong event appears unlikely.