Sea surface temperature (SST) forecasts for Sept – Nov 2021 continue to indicate cooling conditions across the equatorial Pacific (Fig. 1). Current Nino 3.4/4 anomalies are neutral (Fig. 2), and ENSO outlooks note the persistence of neutral conditions in the short term, with lingering uncertainty as to whether La Niña conditions could emerge in winter 2021-2022, or whether conditions would not reach relevant La Niña thresholds and remain ENSO-neutral.
Forecast Roundup: On Aug 11, the Japanese Meteorological Agency (JMA) observed ongoing ENSO-neutral conditions, and called for a 60-percent chance of neutral conditions continuing to autumn. On Aug 12, the NOAA Climate Prediction Center (CPC) ENSO was at “La Niña Watch” status, with a 60-percent chance of ENSO-neutral through September, and a 70-percent chance of La Niña emerging in Nov-Jan. On Aug 12, the International Research Institute (IRI) issued an ENSO Quick Look (Fig. 3), noting a mix of “atmospheric variables consistent with ENSO-neutral conditions” along with “others (that) may hint at cooling to come”. They observed ENSO-neutral was likely through fall, but “with greater uncertainty later in the year”. On Aug 17, the Australian Bureau of Meteorology ENSO tracker was neutral/inactive, stating ENSO “remains neutral with most oceanic and atmospheric indicators within the neutral range”, but noted both likely cooling in the Pacific SSTs into Fall 2021, and uncertainty in the models as to whether this would last for more than a month or two. The North American Multi-Model Ensemble (solid & dashed black line, Fig. 4) is ENSO-neutral, and is expected to remain neutral through summer, but then reach or surpass La Niña levels in late 2021 and into 2022.
Summary: The seasonal forecasts are more or less certain that ENSO-neutral conditions will persist through the summer and into fall. Some forecasts are leaning into a possible return of La Niña in late 2021 given the forecast for oceanic cooling in the equatorial region. Other forecasts are still grappling with uncertainty in the models, along with emergent questions about whether cooling conditions would last long enough to be classified as a La Niña event. La Niña winters are frequently warmer and drier than average in the Southwest, so this forecast is something to watch, given drought conditions and cumulative precipitation deficits in the region.
- 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