Madden Julian Oscillation Returns to Indian Ocean but Continued East Shift to Erode La Nina May Not Happen

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Discussion: The latest Nino SSTA observations reveal that last week La Nina weakened slightly. The slight weakening is characteristic of the past several weeks due to the influence on ENSO of a transient Madden Julian oscillation (MJO) through the equatorial East Pacific. This scenario also slightly weaned the multivariate ENSO index to -1.3 in December although that value continues to identify a moderate-to-strong La Nina climate pattern. In the subsurface, upper ocean heat east of the Dateline steadily decreased from a peak during AUG-NOV 2022 (Fig. 1). However, that less cool trend may be halting as a new cool zone is recently developed between 155W and 125W. As previously stated, a transient MJO through the eastern equatorial Pacific Ocean weakened La Nina slightly. However, the ECMWF 30-day MJO forecast indicates MJO shifts across tropical Africa now and into the Indian ocean and intensifies the next 2 weeks and then stalls and weakens rather than shifting through the eastern equatorial Pacific Ocean (Fig. 2). Implied is the necessary shift of MJO through the East Pacific tropics in late JAN/early FEB may not happen. Consequently, additional weakening of La Nina may not occur. The southern oscillation index (SOI) briefly tumbled to negative phase late last week/weekend and is now neutral and forecast to return to a robust positive phase the next 2 weeks (Fig. 3). The +SOI return suggests La Nina may gain some strength. The pro-La Nina short-term signs have caused 6 of the 8 most recent members of the NCEP CFS V2 Nino34 SSTA forecast for 2023 to doubt an expected shift into El Nino later in 2023 (Fig. 4). The ENSO phase forecast for 2023 is precarious!

Fig. 1: Subsurface upper ocean heat across the equatorial Pacific Ocean.

Fig. 2: Latest 30-day MJO forecast by ECMWF.

Fig. 3: The 16-day southern oscillation index forecast using all operational models.   

Fig. 4: Latest NCEP CFS V2 Nino34 SSTA forecast reveals the most recent (blue) 6 of 8 ensemble members doubt a 2023 El Nino.