June 2018 SW Climate Update - ENSO Tracker

Oceanic and atmospheric conditions remained ENSO-neutral over the last month (Figs. 1-2), and most ENSO forecasts and outlooks reflect these conditions. On June 5, the Australian Bureau of Meteorology maintained its ENSO Outlook at “inactive,” with neutral conditions likely to persist through summer. However, the agency noted that models forecast warming conditions in surface temperatures in the tropical Pacific Ocean—a precursor to the emergence of an El Niño event. On June 11, the Japanese Meteorological Agency (JMA) saw an end to lingering La Niña conditions in spring 2018, a 70-percent chance of ENSO-neutral conditions over summer, and a 50-percent chance of either El Niño or neutral conditions this fall. On June 14, the NOAA Climate Prediction Center (CPC) issued an El Niño watch even while short-term conditions were expected to remain ENSO-neutral. CPC indicates a 50-percent chance of an El Niño event developing this fall and a 65-percent chance of El Niño conditions this winter. Similarly, but with earlier timing, the International Research Institute’s (IRI) June 19 ENSO Quick Look calls for a 50-percent chance of an El Niño event this summer and a 65-percent chance of El Niño over the fall. IRI predicts the event to be weak initially but to potentially reach moderate strength during the fall and winter. The North American Multi-Model Ensemble (NMME) returned to ENSO-neutral conditions, and despite uncertainty over the latter half of 2018, also is increasingly suggestive of a weak to moderate El Niño event by the end of 2018 (Fig. 3).

Summary: As recently as last month, ENSO-neutral conditions were seen as a near-certainty over summer. Forecasters are increasingly bullish on the likelihood of an El Niño event by the end of 2018, and more recent outlooks have increased the chances of an earlier start. A closer look at how these forecasts compare to climatology captures how these seasonal forecasts compare to long-term patterns. The most recent IRI plots indicate a roughly 65-percent chance of El Niño (Fig. 4, red bars), which is approximately 30 percent higher than climatology (red line), while the roughly five-percent chance of La Niña (blue bars) is about 30 percent below climatology (blue line). This illustrates that 1) an El Niño event is increasingly possible by the end of 2018, but it is far from certain; 2) a La Niña event is all but impossible; and 3) the chance of ENSO-neutral conditions is roughly equivalent to climatology. It is still relatively early, but current indications are now favoring the formation of an El Niño in 2018.

Online/Image 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