Fig. 1: The Pacific decadal oscillation has a tendency to parallel the ENSO phase. The coolest PDO monthly index since late 2013 occurred last month. Will La Nina evolution follow later this year?
Discussion: There is a tendency for the Pacific decadal oscillation (PDO) to run parallel with El Nino southern oscillation (ENSO). In February, the PDO index shifted into the cool phase (-0.62) and coolest value since late 2013. Historically, ENSO drives the PDO regime. However, given the weaker ENSO and PDO regimes of recent years that relationship is not necessarily completely active. Nevertheless if the cool PDO continues, ENSO phase is likely to trend toward La Nina which is forecast by several models for later this year. If that regime develops the timing of onset is quarter 3 of 2020. The initial primary concern is the increased risk this pattern brings for a very active hurricane season in the North Atlantic. NOAA identifies the primary La Nina climate anomalies around the world for both winter and summer (Fig. 2).
Fig. 2: The NOAA La Nina climate anomalies for around the world in both winter and summer.