Executive summary: During APR/MAY 2022, the multivariate ENSO index (MEI) dipped to -1.7 which indicates the strongest La Nina atmosphere of the 2020-22 La Nina episode is taking place now (Fig. 1). The Nino34 SSTA also dipped slightly to -1.1 in May. Although oceanic parameters are of moderate La Nina intensity, the strong La Nina atmosphere is likely triggered by the sharp contrast in strong subsidence across the East Pacific tropics compared with an energetic convective regime across the far West Pacific as identified by the May 2022 monthly velocity potential analysis from IRI/LDEO (Fig. 2).
Fig. 1: The multivariate ENSO index (MEI) dipped to -1.7 during APR/MAY, the strongest La Nina climate signature of the 2020-22 La Nina episode.
Fig. 2: Typical of a La Nina climate, and more amplified than usual, strong positive (negative) velocity potential is located in the East Pacific (West Pacific). The sharp differences help to explain the vigorous La Nina climate pattern.
Discussion: The East Pacific equatorial region certainly maintains La Nina although during the past 2-4 weeks the (La Nina) signature is weakening (Fig. 3). However, the strong La Nina climate is likely to continue due to the extremely warm SSTA north of Australia and the influence the warm/cool SSTA contrast across the equatorial Pacific has on the atmospheric pattern.
Often the key to ENSO phase ahead is the trend in the equatorial Pacific subsurface temperature regime. Interestingly, Australia Bureau of Meteorology forecasts La Nina to end (Fig. 4) and their warming eastern equatorial subsurface Pacific Ocean analysis supports that claim (Fig. 5). Alternatively, NOAA maintains weak La Nina for 2022 (Fig. 6) citing a cooler subsurface eastern equatorial Pacific analysis (Fig. 7).
Due to the PERSISTENT and ROBUST convection pattern across the equatorial Pacific supported by monthly potential velocity analysis, Climate Impact Company is forecasting La Nina to continue through JUN/JUL/AUG and linger into SEP/OCT/NOV with uncertainty for the last third of the year (Fig. 8).
Conclusion: Although the Nino34 SSTA component of ENSO may shift to neutral phase during Q3 of 2022, the La Nina climate will continue into at least September. The forecast is very uncertain beyond that point. The La Nina climate will enhance the 2022 North Atlantic tropical cyclone season. Of course, land-falling tropical cyclones can easily erase a drought regime. However, prior to that risk, expanding U.S. drought including the West and parts of the Central and East Coast States is likely (which of course increases heat risk). La Nina climate influences elsewhere include more dryness for Argentina into Brazil (while northern South America is soaking wet) and a robust wet climate for Indonesia and Australia.
Fig. 3: Global tropical SSTA analysis provided by SVWM.
Fig. 4: Australia Bureau of Meteorology Nino34 SSTA forecasts yields neutral ENSO phase ahead.
Fig. 5: The equatorial subsurface temperature anomalies across the Pacific Ocean are warm in the East according to Australia Bureau of Meteorology.
Fig. 6: NCEP CFS V2 Nino34 SSTA forecast indicates La Nina persists through the end of 2022.
Fig. 7: NOAA equatorial subsurface Pacific Ocean temperature anomalies indicate lingering cool in the East Pacific.
Fig. 8: The Climate Impact Company probabilistic ENSO phase forecast through DEC/JAN/FEB 2022-23.