Relentless La Nina-Style SOI and MEI Marches On!

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Highlight: Oceanic La Nina weakening BUT La Nina climate remains strong!

Fig. 1: A 2-year-long strong La Nina signature of the southern oscillation index and multivariate ENSO index is likely to continue.

Discussion: The monthly southern oscillation index (SOI) for June is projected near +1.65 which is a robust La Nina signature (Fig. 1). The multivariate ENSO index (MEI) which is a measure of the atmospheric response to equatorial SSTA is also likely to stay in a strong La Nina mode for June (due to the SOI influence). The observations are dramatic due to the oceanic La Nina weakening to near neutral phase recently (Fig. 2) and forecast to weaken slightly over the next 1-2 months (Fig. 3). The La Nina climate is in-place due to the dramatic contrast of warming SSTA in the East Indian/West Pacific tropics compared to the relative cool Central/East Pacific tropics (Fig. 4). The dramatic SSTA difference fuels tropical convection which releases latent heat pole ward shaping the global climate. The equatorial SSTA regime described is a classic La Nina motivator despite the Nino34 SSTA shifting toward normal. Because the climate pattern wants to stay in La Nina mode, forecast models indicate oceanic La Nina will regenerate late summer/early autumn and last into winter. NOAA models indicate the 2020-22 La Nina could reverse toward El Nino in 2023.

Fig. 2: The last 12 weeks of Nino SSTA observations, note Nino34 trending toward the La Nina threshold.

Fig. 3: NOAA Nino34 SSTA forecasts indicate La Nina may weaken (briefly) to neutral phase and is likely to return to La Nina for late summer to late 2022.

Fig. 4: A dramatic SSTA difference has formed across the tropical Pacific Ocean.