Oceanic La Nina Weaker/Atmospheric La Nina Still Strong but Transient January MJO Could Weaken La Nina Climate

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Highlight: Oceanic La Nina is weaker, atmospheric La Nina still strong. But transient January MJO could weaken La Nina climate.

Fig. 1: Comparing the monthly Nino34 and MEI for the 2020-22 La Nina and upper ocean heat in the equatorial Pacific Basin.  

Discussion: Once again, the equatorial Pacific upper ocean heat is warming into the neutral range (Fig. 1). During the 2020-22 La Nina episode, upper ocean heat has surprisingly been choppy with cool strongly supportive of La Nina peaks in November 2020 and May 2022 and also uncharacteristic warming in May 2021 March to May of 2022. The current equatorial Pacific upper ocean heat is very similar to one year ago when forecast models were projecting El Nino for 2022 as they are now for 2023. Meanwhile, the Nino34 SSTA maintains a moderate La Nina signal and multivariate ENSO index (MEI) has shown moderate to strong La Nina climate intensity since the middle of 2022. The daily southern oscillation index (SOI) has recently been steadily signaling a robust La Nina climate continues. However, the Madden Julian oscillation (MJO) is making an attempt at crossing the equatorial Pacific during the first half of January. Consequently, the SOI is expected to respond by shifting to the negative phase for the middle third of the month (Fig. 2). If so, upper ocean heat in the equatorial East Pacific should continue to warm and oceanic La Nina will weaken. Currently, the Nino SSTA regions are showing steady slight decay of La Nina (Fig. 3). A collection of ENSO forecast models reveal that by May, ENSO is in neutral phase with extended-range forecasts by POAMA, ECMWF and NCEP CFS V2 showing marginal weak El Nino (Fig. 4).

Fig. 2: The 15-day southern oscillation index forecast utilizing all models.  

Fig. 3: The 12-week tracking of the Nino SSTA regions.  

Fig. 4: Collection of ENSO forecast models by POAMA for May 2023 and a glimpse at what the August 2023 forecast by BOM, ECMWF and NOAA will be.