What is an El Niño?
El Niño is one of three phases of the El Niño-Southern Oscillation (ENSO). More specifically, it is a pattern of warmer temperatures in the Pacific Ocean. These warmer temperatures result in air motions that are offset above the earth’s surface from where they normally would be. This has different effects on the weather patterns for different locations across the globe.
What does warming of the ocean do?
The most important effect is the offset of warm rising air from the normal positioning. This combines with the fact that this offset also causes an offset in the precipitation areas. The following image depicts the offset of temperatures from normal for El Niño and its opposite phenomena La Niña, and how that causes a shift in where convection occurs.
What is its impact on the weather?
This is a complicated answer and one that is still actively studied by research meteorologists. Early research has shown that climate patterns are linked to El Niño conditions. These patterns are displayed on the map below for a period of December through February of an El Niño year
As the above image illustrates, El Niño conditions have more impact on areas near the equator than they do in other areas. The effects are normally seen during the winter as the Pacific Ocean’s conditions deviate the from normal the most during this time. Areas closest to the Pacific Ocean see the highest impact from the system due to their proximity to the oscillation. However, the effects are global and year-round.
Current Stage and Beyond
Currently we are in the Neutral phase of ENSO with no changes soon; however, many numerical models are favoring a transition into the El Niño phase by September. NOAA forecasters predict a 50% chance of El Niño occurring, with a 40% chance of staying in Neutral phase, while only a 10% chance of going to a La Niña phase by September. The below graphic shows model output of the Pacific Ocean temperatures throughout multiple models and statistical analysis.
Looking at the graph it can be seen that most models favor an above average temperature throughout much of the year through November, with only 2 models showing below normal temperatures for an extended period time. However, only significant departures (greater than 0.5ºC) from normal temperature are normal El Niño characteristics. Thus, while confidence remains high that above normal temperatures will occur in the Pacific Ocean, it is yet to be seen if it will be enough to be called an El Niño.