ENSO Tracker - Apr 2021
Sea surface temperature (SST) forecasts for May – July 2021 return to normal conditions across the equatorial Pacific (Fig. 1). The current Nino 3.4/4 anomalies show the trend, as they continue toward (or have reached) neutral conditions (Fig. 2). International climate outlooks note the imminent end of this La Niña event, with ENSO-neutral conditions likely to persist through summer.
Forecast Roundup: On Apr 8, the NOAA Climate Prediction Center (CPC) ENSO status was at La Niña Advisory, owing to negative SST anomalies. The CPC called for an 80-percent chance of ENSO-neutral during May-July 2021. On Apr 8, the International Research Institute (IRI) issued an ENSO Quick Look (Fig. 3), noting ENSO-neutral SSTs and “the evolution of most key atmospheric variables are consistent with weakening La Niña conditions.” On Apr 9, the Japanese Meteorological Agency (JMA) observed that “La Niña features are decaying”, with a 70-percent chance of neutral conditions over summer. On Apr 13, the Australian Bureau of Meteorology ENSO tracker was fully shifted to neutral/inactive. They cited warming surface and subsurface ocean temperatures, and ENSO-neutral atmospheric conditions. The North American Multi-Model Ensemble (solid and dashed black line, Fig. 4) are (barely) ENSO-neutral, and are expected to remain neutral for the next several months.
Summary: La Niña conditions have rapidly transitioned to ENSO neutral conditions, with the expectation these will remain in the range of neutral through at least summer. Given the current NMME forecast, and past event behavior, forecasters will keep an eye on conditions to see whether winter 2021-2022 might be a double-dip of La Niña (where a short period of neutral conditions are bookended by La Niña events).
- 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