Highlight: Nino34 SSTA shifts to weak La Nina SSTA.
Discussion: Suddenly, both the Nino34 and Nino3 (east-central/east equatorial Pacific Ocean) regions cool to the La Nina threshold of -0.5C last week (Fig. 1). The cooler SSTA are linked to cooler upper ocean heat in the east-central Pacific last week (Fig. 2). The NCEP CFS V2 forecast indicates La Nina returns by early autumn (Fig. 3). A redeveloping La Nina would propel anticipated above normal 2021 North Atlantic tropical cyclone activity higher than currently indicated. The ENSO regime remains changeable and the short-term cooling may not indicate La Nina regeneration for later this year (yet).
Fig. 1: The Nino SSTA regions and their weekly anomalies for the past 12 weeks identify sudden weak La Nina characteristics for Nino34/Nino3 regions.
Fig. 2: The upper ocean heat suddenly diminishes in the east equatorial Pacific.
Fig. 3: NCEP CFS V2 forecasting La Nina to return in early autumn.