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Southwest Climate Outlook El Niño Tracker - September 2018 | CLIMAS


Southwest Climate Outlook El Niño Tracker - September 2018

Thursday, September 20, 2018

With little change from last month, the Southwest remains in an ENSO holding pattern. Oceanic and atmospheric conditions are still within the range of ENSO-neutral (Figs. 1-2), but the forecasts point toward the likely emergence of an El Niño event this fall and lasting into the winter. On Sept. 10, the Japanese Meteorological Agency (JMA) identified continued ENSO-neutral conditions in oceanic and atmospheric indicators, with a 60-percent chance of El Niño developing this fall. On Sept. 11, the Australian Bureau of Meteorology maintained its “El Niño Watch;” most indicators are within the range of neutral, but models suggest a warming tropical Pacific in the coming months. The agency predicts a 50-percent chance of El Niño formation by the end of this year. Similarly, on Sept. 13, the NOAA Climate Prediction Center (CPC) continued its El Niño watch, identifying persistent neutral conditions now but with seasonal outlooks and models predicting the emergence of an El Niño later this year. Based on these models, the current forecasts call for a 50- to 55-percent chance of an El Niño event developing this fall, and a 65- to 70-percent chance of El Niño conditions this winter. On Sept. 13, the International Research Institute (IRI) issued its ENSO Quick Look, also indicating continued neutral conditions in the oceans and atmosphere currently, but calling for a nearly 70-percent chance of an El Niño event by the end of 2018 (Fig. 3). The North American Multi-Model Ensemble (NMME) has stabilized over the past few months but continues to indicate warmer-than-average ocean temperatures and the likelihood of a weak El Niño event by the end of 2018 (Fig. 4).


Summary: Despite persistent ENSO-neutral conditions, most outlooks have held steady in predicting the most likely outcome for late 2018 to be the formation of an El Niño event. With forecast probabilities between 50 and 70 percent and the continued discussion of this event, it starts to feel as though an El Niño is likely. Given the effectively zero-percent chance of a La Niña event, the remainder of these forecast probabilities call for an ENSO-neutral fall and winter (2018-2019), with a 30- to 50-percent chance of neutral conditions through early 2019. A few of the forecasts noted that while the current oceanic and atmospheric indicators are neutral, they are seeing something in the models that gives them (relative) confidence of an El Niño event by the end of 2018. Such events have fizzled before, however, so given the relative weak strength of the current trends towards El Niño conditions, we would be wise to just wait and see how conditions develop over the next few months.


Online Resources

  • Figure 1 - Australian Bureau of Meteorology -
  • Figure 2 - NOAA - Climate Prediction Center -
  • Figure 3 - International Research Institute for Climate and Society -
  • Figure 4 - NOAA - Climate Prediction Center -