La Nina Arrives; Looks Like La Nina Modoki

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NOAA/CPC announced yesterday (Oct. 14) that La Nina onset developed in October 2021. The surface/subsurface cool anomalies in the equatorial East Pacific suggest La Nina Modoki. The projected ENSO West-East index (WEI) for October suggests La Nina Modoki. The La Nina episode is forecast to last into early northern hemisphere spring 2022.

Executive Summary: NOAA/CPC announced onset of La Nina yesterday. The Climate Impact Company ENSO forecast (based on an analog) indicates La Nina lasts into April 2022 followed by a long duration neutral ENSO for the remainder of 2022 through middle 2023 (Fig. 1). The “caveat” forecast is El Nino for late next year. A third repeat of La Nina later in 2022 is not likely. Currently, the SSTA pattern across the equatorial East Pacific reveals a cool bias toward the Dateline rather than the northwest coast of South America (Fig. 2). The SSTA signature described is evidence of rare La Nina Modoki. In the subsurface, the upper ocean heat is cooler than at peak intensity of the 202-21 La Nina episode (Fig. 3). Implied is La Nina 2021-22 could be stronger than the 2020-21 episode although the analog forecast (and dynamic models) do not indicate that scenario. The subsurface cool anomaly is strong and biased farther west than usual (Fig. 4) also supportive of La Nina Modoki. In October, the Climate Impact Company ENSO West-East Index (WEI) is projected to enter La Nina Modoki status (Fig. 5). Unlike the handful of well-defined El Nino Modoki episodes in the 1950-2021 climatology, La Nina Modoki is rare. The most recent La Nina Modoki events were early in the year of 2008 and 2012. Briefly, La Nina Modoki occurred in early 1989. The climate bias of La Nina Modoki during those few analog years was a wetter winter climate for Texas to the Mid-south U.S. compared to normal La Nina, wetter for Brazil and Argentina compared to normal La Nina and in Australia the wet bias was across the northwest, north and East Coast.

Fig. 1: Climate Impact Company constructed analog forecast of ENSO phase using Nino34 SSTA. Source: CIC.

 

Fig. 2: The cool SSTA in the equatorial East Pacific are biased toward the Dateline – a signal that La Nina Modoki is forming. Source: NOAA.

Fig. 3: The upper ocean heat anomalies are cooler than the peak of the 202-21 La Nina episode. Source: NOAA.

Fig. 4: The equatorial East Pacific subsurface cool anomaly is located farther west than usual for La Nina which is supportive of La Nina Modoki. Source: NOAA.

Fig. 5: The CIC ENSO West-East Index which measures whether a Modoki ENSO event is present shifts toward borderline La Nina Modoki in October 2021. Source: CIC.