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Weak El Niño Conditions Are Present

15.2.2019

El Niño conditions formed during January 2019, based on the presence of above-average sea surface temperatures (SSTs) across most of the equatorial Pacific Ocean (Fig. 1) and corresponding changes in the overlying atmospheric circulation.  The weekly Niño indices remained above average during the month, although decreasing in the Niño-3 and Niño-3.4 regions.  However, the Niño-4 region remained elevated, with a value of +0.8°C in early February. 

Positive subsurface temperature anomalies (averaged across 180°-100°W) increased in the last couple weeks in association with a downwelling Kelvin wave that contributed to above-average temperatures in the central Pacific.  Compared to last month, the region of enhanced equatorial convection expanded near the Date Line, while anomalies remained weak over Indonesia.  

Low-level wind anomalies became westerly across the western Pacific Ocean, while upper-level wind anomalies were mostly westerly over the eastern Pacific. The equatorial Southern Oscillation index was negative (-0.6 standard deviations).  Overall, these features are consistent with borderline, weak El Niño conditions. 

The majority of models in the IRI/CPC plume predict a Niño 3.4 index of +0.5°C or greater through at least the Northern Hemisphere spring 2019. Given the recent downwelling Kelvin wave and the forecast of westerly wind anomalies, most forecasters expect SST anomalies in the east-central Pacific to increase slightly in the upcoming month or so.  Because forecasts through the spring tend to be more uncertain and/or less accurate, the predicted chance that El Niño will persist beyond the spring is 50% or less.  In summary, weak El Niño conditions are present and are expected to continue through the Northern Hemisphere spring 2019 (~55% chance).

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