At long last, is El Nino coming?

Hey there El Niño, it's been a minute! Your sister La Niña had been dominating the Pacific for the past three years. Is it finally time for the warm phase of the El Niño Southern Oscillation, or ENSO, to return? Scientists at the Climate Prediction Center seem to think so. An El Niño Watch has been declared, with the CPC reporting a 62% chance of ENSO-positive conditions developing by the summer.

From January through March, sea surface temperatures in the Niño regions (more on that later) were just slightly below average, signaling a shift into the ENSO Neutral phase. This is the first time since the Fall of 2020 that the La Niña threshold of -0.5°C was not met for three consecutive months. And forecast models are nearly unanimous that the upward temperature trend toward El Niño will continue: 

Forecast model projections for sea surface temperature (SST) anomaly in the Niño 3.4 region.

(Chart from Columbia Climate School IRI for Climate and Society)

Before we dive into the possible impacts of an El Niño summer on the Tri-State, let's define the phenomenon. The onset of El Niño is declared when the surface water in the equatorial Pacific is warmer than average for at least three consecutive months. The map below shows the Niño regions, or specific areas that are closely monitored for ENSO: 

Map of Nino regions from Climate.gov

El Niño is triggered by a weakening of trade winds that normally push warm water away from the coast of equatorial South America. When these winds are weaker, warm water gets trapped along the coastline. The subsequent impacts of this seemingly subtle change can be felt worldwide. 

In the Tri-State area, the impacts of El Niño in the summertime can be subtle. 

Map of El Niño impacts for June through August.
 (Image from Climate.gov)

According to the map above, NOAA does not attribute El Niño to any meaningful change in summertime temperatures or precipitation in the continental USA. However, we can look for clues in previous ENSO-positive summers in the Tri-State. Data from the local National Weather Service office shows that, in this century, summer temperatures were below average in almost every El Niño year. The only exception was during the "Super El Niño" summer of 2015, when temperatures along the equatorial Pacific were nearly 2°C above average, far exceeding the +0.5° threshold. There's not a strong precipitation signal coming from recent El Niño summers, either. Only one stands out, 2009, which was a summer with marginal El Niño conditions. 2009 is still the 4th-wettest summer on record at Central Park. In particular, June was drenched by over ten inches of precipitation, with rain falling on 18 separate days in the month. (Incidentally, this was the same year as "The Summer That Isn't" in New York. Remember that?) 

El Niño conditions tend to have a noticeable impact on Tri-State winters, usually leading to above-average temperatures and rainfall. But, that doesn't mean an El Niño winter is snow-free, as this phase of ENSO tends to bring us more coastal storms like Nor'Easters. In fact, the record-breaking blizzard in January 2016 occurred during the same "Super El Niño" mentioned above! 

One thing that's well documented is the impact of ENSO on hurricane seasons. The tropics tend to be less active during an El Niño, and it has to do with wind shear. In the ENSO-positive phase, the unusually warm water off the west coast of South America repositions the southern jet stream over the Caribbean and subtropical Atlantic, introducing higher wind speeds to the upper atmosphere in this region. Stronger upper-level winds are disruptive to tropical storms, which rely on light wind speeds through the entire vertical column of the atmosphere to strengthen. Learn more about hurricane development here. 

El Niño events typically last for several months to over a year. The La Niña event that ended in March was a bit long for the cool phase of ENSO, but it could be a sign of an overall trend toward a semipermanent La Niña phase.