As the naturally occurring El Niño of 2015-2016 wends down, NOAA is forecasting this week that conditions in the Pacific Ocean will likely flip from an El Niño to a La Niña, lowering temperatures worldwide this fall and winter. The now-dissipating El Niño is part of ENSO, or the El Niño-Southern Oscillation, a natural climate pattern where the tropical Pacific Ocean’s sea surface temperatures (SSTs) swing between warmer-than-normal (El Niño) and colder-than-average (La Niña) temps. This recent El Niño is the primary reason we saw above-normal temperatures for the latter months of 2015 and first few months of 2016.
Earth’s naturally occurring ENSO, NOAA writes, can influence everything from “wind, air pressure, and rain throughout the tropics” and “can have cascading side effects around the whole globe.” It also impacts the “mid-latitude jet streams that guide storms towards the United States.”
As the strong El Niño that has been affecting global weather begins to unravel, measurements show a “blob” of colder water now pushing its way toward the ocean’s surface, replacing the warmer surface temperatures of the tropical Pacific (see video).
This cooler water has been “sliding slowly eastward for the past couple of months,” and this “massive, slow-motion wave is a favorable sign that La Niña—the cool phase of the ENSO climate pattern—might develop.” The two phenomena swing “back and forth every 3-7 years on average.”
This seesawing between El Niño and La Niña tends to affect the Atlantic and eastern Pacific hurricane seasons as well. As time moves on, the cooler water starts to replace the warmer water near the Pacific Ocean’s surface and if it persists for at least five months, a La Niña develops. Currently, the National Oceanic and Atmospheric Administration (NOAA) has issued a watch for a La Niña expected to develop over the summer and into the fall.