From October to December 2018, sea surface temperatures across the east-central tropical Pacific were at weak El Niño levels. However, the atmosphere failed to respond to these warmer-than average sea surface temperatures, indicating a lack of the coupling of ocean and atmosphere needed to reinforce an El Niño event and to trigger the atmospheric circulation changes and climate impacts away from the tropics. Subsequently, sea surface temperatures cooled to slightly below El Niño thresholds during late January up to mid-February 2019. However, during February the atmosphere began to show some El Niño-like patterns, including weakened trade winds in the western and central tropical Pacific and above-average cloudiness and rainfall near the International Date Line. This could mean that coupling of the atmosphere to the warmed sea surface temperatures has commenced, increasing the chances of a weak El Niño being maintained in the coming few months.
The temperature of waters below the surface of the tropical Pacific, from the west-central Pacific eastward and extending to several to hundred meters below the surface, has been above average during most of 2018, continuing through to the present. This deeper warm water, which has extended to the surface at times, is a typical pre-cursor for El Niño events. Thus, the currently observed borderline El Niño-level sea surface temperatures are likely to continue, and may strengthen to weak El Niño levels during March and April.
Consistent with the likelihood of a return of the sea surface temperatures to weak El Niño levels, around two thirds of the model forecasts from WMO Global Producing Centres of Long Range Forecasts suggest that the recent coupling of the atmosphere to the ocean may sustain a weak El Niño into the second quarter of 2019. Model predictions of the strength of the El Niño, as characterized by the departures of sea surface temperatures in the east-central tropical Pacific, range from approximately 0.6 to 0.9 degrees Celsius above average during March-May. Based on the model predictions and expert assessment, the probability for an El Niño condition to occur is estimated at about 50–60% for March–May, and about 40–50% for June–August 2019. However, outlooks made at this time of the year are particularly uncertain beyond the second quarter and should be considered with caution. Even if ocean conditions do remain at El Niño levels for the next several months, the chance for a strong event (sea surface temperatures in the east-central tropical Pacific rising to at least 1.5 degrees Celsius above average) during this period is low.
It is important to note that El Niño and La Niña are not the only factors that drive global climate patterns, and that the strength of El Niño/Southern Oscillation (ENSO) does not automatically correspond to the strength of its effects. At the regional level, seasonal outlooks need to assess the relative effects of both the ENSO state and other locally relevant climate drivers. For example, sea surface temperatures of the Indian Ocean, the southeastern Pacific Ocean and the Tropical Atlantic Ocean are also known to influence the climate in the adjacent land areas. Regionally and locally applicable information is available via regional and 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).