East Pacific Kelvin Wave Fading; La Nina Regains Some Strength

Fig. 1: The Nino SSTA regions for the past 12 weeks. The Nino12 region off the northwest coast of South America is much cooler.

Discussion: During the past 2-3 weeks the convective phase of the Madden Julian oscillation (MJO) has dominated the eastern Indian Ocean/West Indonesia tropics. The general rising air induced by convection along this stretch is replaced by increasing easterly trade winds arriving from the central/eastern equatorial Pacific. The trade wind increase in the central/eastern equatorial Pacific has caused up-welling of cool subsurface water to cause La Nina to gain some strength. Additionally, the subsurface (warm) Kelvin Wave present in January/February which caused some decay of La Nina is weakening. The equatorial East Pacific subsurface is now a mix of both warm and cool anomalies and cooler waters have made gains during the past 10 days. In the equatorial West Pacific, a new subsurface Kelvin Wave may be forming. La Nina events normally break down due to the passage of 2-3 warm Kelvin Waves in the subsurface equatorial Pacific. The just-now fading Kelvin Wave weakened La Nina but did not dissipate cold ENSO. Consequently, we await the next Kelvin Wave to shift into the equatorial East Pacific which should take about 4-6 weeks to occur. Until then, La Nina is steady or may strengthen slightly with the next weakening phase likely in April.

Fig. 2: The subsurface equatorial Pacific Ocean temperature anomalies identify a La Nina-defeating Kelvin Wave in the East Pacific as weakening while a new Kelvin Wave is forming in the West Pacific.   

Fig. 3: The Australia Bureau of Meteorology ENSO phase forecast for 2022.