Based on the latest data, NOAA has released an El Niño advisory showing a rapidly growing El Niño anomaly. A strong El Niño event is expected to develop, with weather impacts spreading across the United States, Canada, and Europe in the Fall and Winter 2023/2024 seasons.
Ocean anomalies have long been known to play an important role in atmospheric circulation and our weather on smaller and larger scales. That is especially true during the Winter season when the pressure systems are strongest.
An El Niño event can also be used as an indicator, not just the cause, as it tells us what the current state of the atmosphere is that produced it in the first place. You will see how El Niño is currently growing and how it is expected to influence the upcoming cold weather season of 2023/2024.
El Niño is a warm phase of the ENSO, which stands for “El Niño Southern Oscillation.” This region of the equatorial Pacific Ocean regularly shifts between warm and cold phases. Typically there is a phase change around every 1-3 years.
The image below shows the ENSO regions across the tropical Pacific. Regions 3 and 4 expand over the east and west tropical Pacific. The main region is seen in the image as the Nino 3.4 region. This is where the main strength of a warm/cold event is calculated from.
Each ENSO phase influences the pressure and weather in the tropics differently. This affects the overall global circulation over time, changing the weather patterns worldwide.
A (cold/warm) phase usually develops between late Summer and early Fall. It then lasts until Spring, but some events can last up to two or three years.
The cold ENSO phase is called La Niña, and the warm phase is called El Niño. Besides the ocean temperatures, one of the main differences between the phases is the pressure patterns they promote, seen below as high (H) and low (L) pressure zones.