Dynamic Models Forecasting Emerging La Nina for AUG/SEP/OCT

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Dynamic global SSTA forecast models including NCEP CFS V2, NMME and GFDL are suddenly forecasting La Nina cooling in the eastern equatorial Pacific Ocean for AUG/SEP/OCT 2019. The possible cause for this sudden change picked up by most global models is the rapid cooling off the West Coast of South America the past few weeks forced northward into the East Pacific tropics by the reactivated Humboldt Ocean Current. The just-ending El Nino warm waters shift west to the Dateline. Interestingly, if the La Nina cooling forecast is less dramatic an El Nino Modoki may form.

Discussion: Suddenly and with great intensity cool surface temperatures emerged off the entire West Coast of South America in late June/early July. The prevailing south-to-north running Humboldt Ocean Current is pushing the chilly water into the eastern equatorial East Pacific. Forecast models have picked up on this and are now forecasting a weak La Nina to develop during AUG/SEP/OCT (Fig. 1).

Of immediate concern is the influence on the tropics. Will the tropical season in the North Atlantic basin be more active as El Nino and associated upper level shear fade? The U.S. climate pattern for an emerging La Nina as autumn approaches favors warmer than normal temperatures for the entire nation with wet conditions on the Gulf Coast and Atlantic Seaboard. The Corn Belt is wet while the southern Plains and West Coast are dry.