Kelvin Wave Emerges, Pushes East of Dateline

Highlight: As expected, influence of MJO is weakening La Nina.

Fig. 1: The 12-week Nino region SSTA observations.

Discussion: During the past couple weeks the Madden Julian oscillation (MJO) was active in the equatorial East Pacific. Consequently, trade winds eased and the southern oscillation index (SOI) turned negative since Jan. 7. The result is some weakening of the Nino SSTA cool anomalies and La Nina is now weakest since onset last autumn (Fig. 1). In the subsurface, emergence of a Kelvin Wave is inspired by the recent MJO event. A layer of anomalous warm water at 125-to-250-meter depth has shifted quickly to the east of the Dateline reaching 140W during the past week (Fig. 2). The warm water accumulation near and east of the Dateline is a Kelvin Wave. East-shifting Kelvin Waves are how La Nina breaks down and if they continue lead to the onset of El Nino. The frequency of Kelvin Wave’s (when active) is every 6-7 weeks. Another Kelvin Wave in March would likely dissipate La Nina. The effectiveness of this Kelvin Wave depends on its transitory nature and whether the west coast of South America is reached over the next 2-3 weeks. If so, La Nina is likely to weaken and barely hang on for late Q1 of 2022.

Fig. 2: Subsurface temperature anomalies in the equatorial Pacific Ocean identify emergence of a Kelvin Wave shifting well east of the Dateline.