ENSO Tracker - Oct 2021

ENSO Tracker - Oct 2021

Sea surface temperature (SST) forecasts for Nov 2021 – Jan 2022 indicate further cooling across the equatorial Pacific (Fig. 1). Monthly Nino 3.4/4 anomalies were neutral (Fig. 2), but most ENSO outlooks now see La Niña conditions as having arrived. These conditions are expected to remain in place through winter 2021-2022, with some confidence they will last long enough to reach the La Niña threshold.

Forecast Roundup: On Oct 11 the Japanese Meteorological Agency (JMA) observed ENSO-neutral conditions continued and called for a 60-percent chance of La Niña conditions in fall and winter. On Oct 12 the Australian Bureau of Meteorology ENSO tracker shifted to La Niña ALERT status “due to continued cooling in the tropical Pacific Ocean and an increase in the number of climate models showing sustained La Niña conditions.” On Oct 14 the NOAA Climate Prediction Center (CPC) ENSO status moved to a “La Niña Advisory” with an outlook calling for an 87-percent chance of La Niña during Dec 2021 – Feb 2022. On Oct 19 the International Research Institute (IRI) issued a Quick Look (Fig. 3), noting “The evolution of key oceanic and atmospheric variables is consistent with La Niña conditions” and issued a La Niña Advisory. The North American Multi-Model Ensemble (solid and dashed black line, Fig. 4) is ENSO-neutral but indicates a rapid swing to moderate La Niña in late 2021 and into 2022. A note that the International Multi-Model Ensemble (IMME) forecast borderline ENSO-neutral through winter.

Summary: The seasonal outlooks have shifted to near consensus on a La Niña event in winter 2021-2022. This is tied to cooling SSTs in the equatorial region, and oceanic/atmospheric coupling indicative of La Niña. The IMME is curious in its divergence from the NMME, but overall consensus centers on a La Niña event of weak to moderate intensity. There are lingering questions about whether conditions will last long enough to be classified as a La Niña event, but each month the forecasts are more confident the conditions will meet that threshold. La Niña winters are frequently warmer and drier than average in the Southwest, so this forecast is something to watch, given the drought conditions and cumulative precipitation deficits affecting the region.

Online Resources

  • Figure 1 - Australian Bureau of Meteorology - bom.gov.au/climate/enso
  • Figure 2 - NOAA - Climate Prediction Center - cpc.ncep.noaa.gov
  • Figure 3 - International Research Institute for Climate and Society - iri.columbia.edu
  • Figure 4 - NOAA - Climate Prediction Center - cpc.ncep.noaa.gov