Southwest Climate Outlook - El Niño Tracker - December 2019

Dec. 22, 2019

Warm waters continue to linger in western regions of the equatorial Pacific (Figs. 1-2), but are expected to fall within the range of ENSO-neutral for winter 2019-2020 and into spring 2020.

Forecast Roundup: On Dec 10, the Japanese Meteorological Agency highlighted a trend towards near-normal sea surface temperatures (SSTs) in the equatorial Pacific, despite recent positive SST anomalies. They maintained their call for a 60-percent chance of ENSO-neutral conditions to continue until spring 2020. On Dec 10, the Australian Bureau of Meteorology noted “abnormally warm sea surface temperatures in the western tropical Pacific” and their influence on regional weather patterns but maintained their ENSO Outlook at ‘inactive’ through early 2020. On Dec 12, the NOAA Climate Prediction Center (CPC) issued their ENSO diagnostic discussion with an inactive alert status and called for a 65-percent chance of ENSO-neutral through spring 2020. They noted that oceanic and atmospheric conditions were “consistent with ENSO-neutral” despite some above average SSTs, especially in the western equatorial Pacific, but forecasters also highlighted a 25- to 30-percent chance of El Niño. On Dec 12, the International Research Institute issued an ENSO Quick Look (Fig. 3), noting recent above normal SSTs had “returned to normal in December” and ENSO-neutral was most likely in 2019-2020, but with “slightly higher chances for El Niño than La Niña”. The Dec 2019 North American Multi-Model Ensemble (NMME) shows the persistent positive SST anomalies in November but is predicted to return and remain within the range of ENSO-neutral through 2019 and into 2020 (Fig. 4).

Summary: Recent positive SST anomalies in the equatorial Pacific are mostly attributed to seasonal variability and not El Niño, although the recent CPC forecast discussion did include a forecast probability for El Niño, so we will keep an eye on any additional developments. The consensus remains that despite recent warming, most oceanic and atmospheric conditions are within the range of ENSO-neutral, and ENSO-neutral remains the most likely outcome for winter 2019-2010. In the Southwest, ENSO-neutral winters have produced some of the wettest and driest winters (and everything in between). We continue to monitor sub-seasonal and short term forecasts for insight into upcoming events. Given recent and long-term drought conditions in the Southwest, a sustained run of regular precipitation events spread out over the cool season would be most welcome.

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