The National Oceanic and Atmospheric Administration has issued an El Niño watch, meaning that conditions are favorable for El Niño conditions to develop in the tropical Pacific Ocean within the next six months.
Why it matters: If an El Niño forms, it would follow one of the most intense such events on record, which teamed up with long-term climate change, to lead to the warmest year ever recorded: 2016. Depending on its exact location in the Pacific and its intensity, the climate phenomenon can reorder weather patterns around the world. On the plus side, it can contribute to increased upper atmospheric winds over the tropical Atlantic, weakening nascent hurricanes and keeping the number of storms lower than they otherwise would be.
Yes, but: Such events can cause droughts and even contribute to political instability as far away as Africa, while sparking deadly flooding in other areas, such as California.
El Niño events also help transport heat from the ocean into the atmosphere, and tend to lead to some of the globe's warmest years. The record warm years of 2015 and 2016 occurred during an intense El Niño event, for example.
NOAA currently forecasts a 50% chance of El Niño developing during the fall, with those odds rising to 65% during the winter. While sea surface temperatures are close to average right now, heat is building up under the surface — a sign that an El Niño may be on its way.