At The Surface La Nina Has Weakened. However, Subsurface Diagnostics Indicate Strengthening!

Small picture: La Nina is weakening. Big picture: La Nina is stronger.

Result: Expect La Nina to regain some strength in April.

Fig. 1: The Nino SSTA regions for the past 12 weeks. Overall, the La Nina signature is the weakest.

Discussion: Combining all Nino SSTA regions and their current temperature anomalies (Fig. 1) yields the least cool (weakest La Nina signature) of 2022 (so far). The Nino34 SSTA region where ENSO phase is monitored is now at -0.9C which is a borderline moderate intensity La Nina. While at the surface, La Nina appears weaker the subsurface tells a different story.

Upper ocean heat in eastern equatorial Pacific Ocean is now cooling and trending toward a more supportive regime of sustaining La Nina (Fig. 2). Previously, a Kelvin Wave moved eastward during JAN/FEB to warm the eastern equatorial Pacific (Fig. 3). The Kelvin Wave has consolidated just-off the northwest coast of South America (Fig. 4) which explains why the Nino12 SSTA region has warmed. Slowly, the Kelvin Wave is eroding.

The Madden Julian oscillation (MJO) has returned to home base, the eastern equatorial Indian Ocean to Indonesia tropics. The convective currents in that region have invited increasing easterly trade winds to replace the rising air and consequently the central equatorial Pacific Ocean has cooled. Additionally, presence of convection in the far equatorial West Pacific coupled with the rising pressure in the eastern equatorial pacific associated with increased trade winds has returned a very La Nina-like southern oscillation index (SOI) forecast to continue through late March,

So, despite the weak La Nina signature at the surface, the +SOI/increased trade wind regime/cooling subsurface tells is that La Nina is likely to gain some strength during late March and into April. Meanwhile, the next Kelvin Wave is forming west of the Dateline. An eastward shift of this feature during APR/MAY is required to breakdown La Nina as climate models is forecasting for late quarter 2 of 2022.

Fig. 2: The upper ocean heat to the east of the Dateline is re-cooling.

Fig. 3-4: The subsurface cool waters in the equatorial Pacific driving the 2021-22 La Nina episode was briefly interrupted by a Kelvin Wave in February into March (left). The Kelvin Wave has reached the northwest coast of South America and is fading (right).