Still A Question Mark…ENSO Pattern Later This Year

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La Nina 2020-21 is barely hanging on as the Nino34 SSTA is right at the La Nina threshold of -0.5C. Other Nino SSTA regions are similar. Neutral ENSO is expected the next 1-3 months and possibly through meteorological summertime. However, there remains a great debate on whether La Nina returns.

Highlight: Still struggling to resolve ENSO for later this year.

Discussion: La Nina 2020-21 is barely hanging on as the Nino34 SSTA is right at the La Nina threshold of -0.5C. Other Nino SSTA regions are similar (Fig. 1). Neutral ENSO is expected the next 1-3 months and possibly through meteorological summertime. However, there remains a great debate on whether La Nina returns. Since 1995 La Nina events of similar or greater strength than the 2020-21 episode have produced a tendency to continue into a second or third year (Fig. 2). Meanwhile the upper ocean heat analysis reveals the current (weak) La Nina should end very shortly as the upper heat in the eastern equatorial Pacific is increasing (Fig. 3). For now, we’re heading for neutral ENSO but La Nina may return later this year.

Fig. 1: The Nino SSTA regime is BARELY hanging onto La Nina.

Fig. 2: La Nina episodes since 1995 according to multivariate ENSO index (MEI). Note that stronger La Nina’s have a tendency to continue while weaker La Nina’s dissipate.

Fig. 3: Upper ocean heat across the equatorial Pacific Ocean and the implications on ENSO phase.