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EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION
CLIMATE PREDICTION CENTER/NCEP/NWS
and the International Research Institute for Climate and Society 13 May 2021
ENSO Alert System Status: Final La Niña Advisory
Synopsis: La Niña has ended, with ENSO-neutral likely to continue through the Northern Hemisphere summer (67% chance in June-August 2021).
During April, the tropical Pacific Ocean returned to ENSO-neutral conditions as the coupling between the atmosphere and ocean weakened. Sea surface temperatures were near-to-below average across most of the equatorial Pacific Ocean in the past month. The Niño indices have generally trended toward normal during the last several months, except for the easternmost Niño-1+2 region, which was -0.7oC in the past week. Subsurface temperature anomalies continued to increase due to a downwelling Kelvin wave, which reinforced the positive temperature anomalies along the thermocline. Low-level easterly wind anomalies were weakly present in the east-centralPacific, but were westerly in the far western Pacific Ocean, while upper-level wind anomalies remained westerly across the central and east-central tropicalPacific. Tropical convection became near average around the Date Line in the past month, with suppressed convection evident over Indonesia. Overall, the ocean and atmosphere system reflected a return to ENSO-neutral.
Most of the models in the IRI/CPC plume predict a continuation of ENSO-neutral through the Northern Hemisphere summer 2021. The forecaster consensus agrees with this set of models through the summer, and then begins hedging toward cooler conditions as the Northern Hemisphere fall approaches. La Niña chances are around 50-55% during the late fall and winter, which is in alignment with forecasts from the NCEP Climate Forecast System and North American Multi-model Ensemble. However, there is typically large uncertainty with forecasts made in the spring, so confidence in ENSO-neutral for the coming seasons is highest. In summary, La Niña has ended, with ENSO-neutral likely to continue through the Northern Hemisphere summer (67% chance in June-August 2021; click CPC/IRI consensus forecast for the chances in each 3-month period).