WMO El Niño/La Niña Update
4 December 2014
Current Situation and Outlook
Steady warming of the tropical Pacific Ocean over the past two months has resulted in ocean surface temperatures reaching weak El Niño levels. However, the overlying atmosphere is showing a mix of responses, with some indicators exceeding El Nino thresholds, while others remain neutral. Models and expert opinion suggest there is approximately a 70% chance that a weak El Niño event will become established before the end of February 2015. If an event does occur, it is most likely to be weak and persist for the first quarter of 2015. Some El Nino-like impacts have already been observed in several countries, and impacts in other areas may develop regardless of whether an El Nino becomes fully established. 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.
In early November, after more than 5 months of warm-neutral to borderline El Niño levels, sea surface temperatures in the east-central tropical Pacific Ocean reached weak El Niño levels. However, despite this oceanic warming, only some of the atmospheric indicators of El Niño have appeared. El Niño is typically associated with and amplified by a difference in the atmospheric pressure between the eastern and western tropical Pacific, and changes in the cloudiness, upper level winds, low level winds, and rainfall across the tropical Pacific. All of these indicators reflect large scale changes in the atmospheric state, which in turn has connections to global weather patterns. At present, the observed changes in these atmospheric indicators are mixed, with some reaching El Nino levels (e.g. surface pressure, upper level winds and, sporadically, the lower level winds) but others remaining closer to normal (most notably, the cloudiness and rainfall patterns). However, heat stored below the surface of the tropical Pacific has clearly increased during November, meaning additional warming of the sea surface is possible in the coming few months. Likewise, average to cooler-than-average ocean temperatures in the far western tropical Pacific combined with increasing eastward positive sea surface temperature anomalies mean west-to-east differences in sea surface temperature anomaly are becoming more El Niño-like than they have been since the possibility of an El Nino first emerged in March/April 2014. Furthermore, some El Nino-like impacts are being observed in parts of South America, Australia, New Zealand, Asia and Africa.
The latest outlooks from climate models and expert opinion favour a weak El Niño in both the ocean and atmosphere during the current season of November 2014 to January 2015, lasting through the northern winter (December to February) and well into the first quarter of 2015. International climate model outlooks suggest a 70% to 75% chance of El Niño during the December to March period. Models also indicate that if an event occurs, it is likely to be weak, though a moderate strength event cannot be completely ruled out. A strong event appears very unlikely. If an El Niño event does occur, the earlier that above-average cloudiness and rainfall appear in the central tropical Pacific Ocean, the greater the likelihood that the event will continue through the first quarter of 2015.
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 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).
The situation in the tropical Pacific and Indian Ocean will continue to be carefully monitored. More detailed interpretations of regional climate variability will be generated routinely by the climate forecasting community over the coming months and will be made available through the National Meteorological and Hydrological Services. For web links of the National Meteorological Hydrological Services (NMHSs), please visit:
For information on WMO Regional Climate Centres (RCCs) and links please visit:
External Links for more information
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