A combined U.S. government climate agency announcement May 13 on Pacific Ocean conditions is easy to understand. The subtitle of this announcement was: "Final La Nina Advisory." And the synopsis continued in that vein: "La Nina has ended, with ENSO-neutral likely to continue through the Northern Hemisphere summer (67% chance in June-August 2021)." (ENSO stands for El Nino-Southern Oscillation, which is the term used to identify the interaction of temperatures and pressure in the equatorial Pacific region.)
The bulletin continues:
"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 Nino indices have generally trended toward normal during the last several months, except for the easternmost region, which was minus 0.7 degrees Celsius 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-central Pacific, but were westerly in the far western Pacific Ocean, while upper-level wind anomalies remained westerly across the central and east-central tropical Pacific. Tropical convection became near average around the International 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 Nina 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 Nina has ended, with ENSO-neutral likely to continue through the Northern Hemisphere summer (67% chance in June-August 2021 ... )"
Agencies issuing the joint announcement are the National Oceanic and Atmospheric Administration (NOAA); NOAA's National Weather Service; and their funded institutions.
The end of La Nina suggests a lower probability of sustained dryness over North America crop regions during the 2021 summer. However, the very dry northern and western crop areas still have no significant precipitation in the forecast for the summer season at this time.
Bryce Anderson can be reached at firstname.lastname@example.org
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