July 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 that. On July 10, the Japanese Meteorological Agency (JMA) identified neutral conditions in oceanic and atmospheric indicators, but with indications of warming oceanic temperatures in the coming months. The agency forecast equal chances (50 percent) of either ENSO-neutral or El Niño by fall 2018. On July 12, the NOAA Climate Prediction Center (CPC) continued its El Niño watch, observing neutral conditions at present, however the warming oceanic temperatures are seen as an indicator of increasing likelihood of El Niño this year. Its outlook calls for a 65-percent chance of an El Niño event developing this fall, increasing to 70 percent this winter. On July 12, the International Research Institute (IRI) issued an ENSO Quick Look that similarly noted neutral conditions in the oceans and atmosphere now and warming oceanic conditions increasing forecast probabilities for an El Niño event to nearly 70 percent by the end of 2018 (Fig. 3). The forecast predicts weak conditions in the initial event development but potentially reaching moderate strength during the fall and winter. On July 17, the Australian Bureau of Meteorology rated its ENSO Outlook at “El Niño Watch.” Most indicators were within the range of neutral, but they too noted steady warming of surface and subsurface waters in the Pacific Ocean that warrant a 50-percent chance of El Niño formation by the end of this year. The North American Multi-Model Ensemble (NMME) also demonstrates the steady trend in observations and forecast toward warmer-than-average ocean temperatures, and is zeroing in on a weak to borderline moderate El Niño event by the end of 2018 (Fig. 4).

Summary: Steady warming in surface and subsurface temperatures in the Pacific led to increasingly bullish forecasts for an El Niño event by the end of 2018, perhaps even sooner. Given the timing and uncertainty in the models and forecasts, the formation of this event is still far from certain, however as mentioned last month, a La Niña event is all but impossible this year. Additionally, the intensity and timing of the event will play a large role in how much it affects tropical storm activity this fall and cool-season precipitation this winter and spring. Most outlooks—for now—are calling for a weak to borderline moderate event.

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