Southwest Climate Outlook - El Niño Tracker - September 2019

Sept. 20, 2019

Forecast Roundup: Seasonal outlooks and forecasts based on sea surface temperature (SST) anomalies (Figs. 1-2) and other oceanic and atmospheric indicators all point towards ENSO-neutral conditions lasting through 2019 and into 2020. On Sep 10, the Japanese Meteorological Agency (JMA) highlighted dissipating warmer-than-normal SSTs and maintained their call for a 60-percent chance of ENSO-neutral conditions to continue until winter 2019-2020. On Sep 12, the NOAA Climate Prediction Center (CPC) issued their ENSO diagnostic discussion, which focused on neutral conditions across the oceans and atmosphere. They called for a 75-percent chance of ENSO-neutral conditions persisting through fall 2019. On Sep 12, the International Research Institute (IRI) issued an ENSO Quick Look (Fig. 3), emphasizing neutral conditions in both oceanic and atmospheric ENSO indicators. Their models see ENSO-neutral as the most likely outcome, but with “slightly higher chances for El Niño than La Niña”. On Sep 17, the Australian Bureau of Meteorology maintained their ENSO Outlook at ‘inactive’ with most oceanic and atmospheric conditions in the range of neutral. The North American Multi-Model Ensemble (NMME) is within the range of ENSO-neutral and is forecast to remain neutral through 2019, with more variability and uncertainty into 2020 (Fig. 4).

Summary & Outlook: ENSO-neutral remains the most likely outcome for 2019 extending into winter 2020. Oceanic and atmospheric conditions returned to within the range of ENSO-neutral, and the ENSO outlooks generally reflect these conditions. In terms of the Southwest, seasonal outlooks had been calling for above average precipitation in late summer and early fall, presumably linked to the increased chance of enhanced tropical storm activity in the eastern pacific associated with El Niño. With a return to ENSO-neutral, the role that El Niño might play in enhancing those pacific tropical storms is no longer in play, but warmer and (mostly) wetter than normal conditions remain in the seasonal outlooks thus far (see Fig. 7 on p. 2). Despite El Niño’s decline to ENSO-neutral, tropical storm activity has picked up in the eastern Pacific Ocean. At the time of this writing, two named storms (TS Lorena and TS Mario), depending on their eventual storm track, are poised to help direct moisture into the Southwest. This could amplify precipitation activity even as the monsoon is on the wane and might even help make up some of the accumulated precipitation deficit of a mostly below average monsoon.

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