Conflicting Signals on ENSO Although La Nina Demise Likely

Discussion: During the past month, the Northeast Pacific has cooled significantly (Fig. 1), and cool phase of the Pacific decadal oscillation (-PDO) has regained strength. The cooler Northeast Pacific is in the face of an El Nino trend forecast by many models. Normally, strengthening -PDO is associated with La Nina. Conversely, NOAA/CPC indicates significant warming is appearing in the subsurface equatorial East Pacific (Fig. 2) indicating significant weakening of La Nina. Additionally, all models forecast a robust phase_7/phase_8 of the Madden Julian oscillation (MJO) episode over the next 2 weeks (Fig. 3) which strengthening the subsurface warming trend to increase El Nino risk as indicated by many models for mid-year (Fig. 4). The 2020-23 global climate is strongly biased by La Nina as indicated by persistent negative phase multivariate ENSO index (MEI) and positive phase of the southern oscillation index (SOI). However, SOI is now neutral, and the 15-day forecast is mostly negative (Fig. 5). During the springtime ENSO prediction barrier, ENSO forecasts are difficult and present diagnostics certainly offer conflicting trends.

Fig. 1-2: In the face of an El Nino trend is a cooler Northeast Pacific SSTA pattern. However, supportive of an El Nino trend is the emergence of anomalous warm water in the equatorial East Pacific subsurface.

Fig. 3: All models indicate a robust phase_8 of the Madden Julian oscillation ahead! A strong MJO P8 should wipe out the remains of La Nina.

Fig. 4: A moderate El Nino is ahead by July according to most dynamic ENSO phase forecast models.

Fig. 5: The southern oscillation index shifts to negative phase over the next 2 weeks, a rarity during the past several years during La Nina. Supported is the demise of the current La Nina.

Climate Impact Company will issue a new 2023-24 ENSO phase forecast later today.