La Nina Modoki Analogs

Fig. 1: La Nina Modoki has formed as the equatorial Pacific cooling associated with La Nina shifts toward the Dateline.

Discussion: A rarely observed La Nina Modoki has developed in the central equatorial Pacific Ocean. Climate Impact Company identifies Modoki using the ENSO West-East Inex (WEI) which simply compares SSTA in the Nino4 region near the Dateline and the Nino3 region in the eastern equatorial Pacific (Fig. 1) away from the moderating effects on SSTA caused by proximity to land off the northwest coast of South America (where the Nino12 SSTA region is located). The La Nina Modoki index is -0.9C for the month of February and the daily index has jumped to -1.23C. The two most recent analogs for Q1/La Nina Modoki are 2001 and 2017 (Fig. 2). Interestingly, the ENSO condition that followed (utilizing the Nino34 SSTA index) produced a weak La Nina to neutral ENSO condition through the middle third of the year followed by potential weak La Nina returning during Q4. The analog is similar with most current operational forecasts. Consequently, despite the development of La Nina Modoki, the ENSO forecast for 2025 is unchanged. Of course, a careful eye on all ENSO diagnostics is warranted as forecast confidence for ENSO 2025 is below average. Usually, the lead catalyst is the subsurface equatorial upper ocean heat anomalies. Currently, cool anomalies east of the deadline at the surface to 200-meter depth are steadily losing intensity (Fig. 3). The fuel to sustain La Nina is diminishing.

Fig. 2: The most recent Q1 La Nina Modoki events and the correlating ENSO phase using the Nino34 SSTA index.

Fig. 3: The subsurface temperatures east of the Dateline in the equatorial Pacific remain cool but somewhat warmer than 1-3 months ago.

.