From October to December 2018, sea surface temperatures across the east-central tropical Pacific were at borderline to weak El Niño levels, but the atmosphere did not respond to the warmed sea surface temperatures, indicating little coupling between the ocean and atmosphere. In January 2019, the sea surface temperatures temporarily dropped to a level near or just below the El Niño threshold, and in February the atmosphere finally began to show some El Niño-like patterns, including weakened trade winds in parts of the tropical Pacific and above-average cloudiness and rainfall near the International Date Line. These more El Niño-like atmospheric patterns helped enable the past-central tropical sea surface temperatures to rise again during February 2019, and the continuation of ocean-atmospheric coupling, although weak, has supported the maintenance of weak El Niño-level sea surface temperatures to the present time.
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, was above average during much of 2018 and early 2019. However, from April onwards into May the temperature of these waters at depth has cooled considerably. This deeper water often precedes the conditions at the ocean surface. Thus, the currently observed weak El Niño-level sea surface temperatures are likely to continue in the short-term, but if the waters below the surface continue to cool, the El Niño may weaken to borderline or neutral levels in the coming several months. However, if the trade winds weaken again, as they have done periodically over the last four months, an increase in the temperature of the waters below the surface could enable current ocean surface conditions to continue well into the second half of 2019.
About two-thirds of the models from the WMO Global Producing Centers of Long Range Forecasts predict ocean temperature patterns to continue at borderline or weak El Niño levels through the June-August period, and over half of them predict continuation through September-November. Model predictions of the strength of the El Niño, as characterized by the departures from normal of sea surface temperatures in the east-central tropical Pacific, range from approximately 0.5 to 0.9 degrees Celsius above average during June-August. Based on the model predictions and expert assessment, the probability of El Niño conditions being maintained is estimated to be about 60-65% through at least June-August, and about 50% for September-November 2019. However, outlooks made at this time of the year are uncertain beyond July or August 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 over 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).