Seasonal hindcasts have previously been demonstrated to show
multi-decadal variability in skill across the twentieth century in
indices describing El-Niño Southern Oscillation (ENSO), which drives
global seasonal predictability. Here, we analyse the skill of predicting
ENSO events’ magnitude and spatial pattern, in the CSF-20C coupled
seasonal hindcasts in 1901-2010. We find minima in the skill of
predicting the first (in 1930-1950) and second (in 1940-1960) principal
components of sea-surface temperature (SST) in the tropical Pacific.
This minimum is also present in the spatial correlation of SSTs, in
1930-1960. The skill reduction is explained by lower ENSO magnitude and
variance in 1930-1960, as well as decreased SST persistence. The SST
skill minima project onto surface winds, leading to worse predictions in
coupled hindcasts compared to hindcasts using prescribed SSTs. Questions
remain about the offset between the first and second principal
components’ skill minima, and how the skill minima impact the
extra-tropics.