AUSTIN (KXAN) — The latest update from the Climate Prediction Center shows an increasing probability of an El Niño pattern by late Summer 2023.
With a long-lasting La Niña in place for the last 3 years, many may now be familiar with the climatological pattern. But what about El Niño? What does La Niña’s counterpart typically bring?
El Niño the basics
Similar to La Niña, an El Niño pattern is determined by analyzing the ocean temperatures along the equatorial Pacific. All of the following criteria must be met for an El Niño to be established:
- Average sea surface temperatures along the equatorial Pacific are at least 0.5°C (0.9°F) warmer than average, beginning the month prior
- The anomaly continues or is expected to continue for 5 consecutive months
- The atmosphere over the tropical Pacific exhibits at least one of the following:
– weaker than normal easterly trade winds
– reduced cloudiness/rainfall over Indonesia and increase in average surface pressure
– increased cloudiness/rainfall in the central or eastern part of the Pacific basin and decrease in average surface pressure
If the criteria are met, an El Niño pattern is said to be in place. The warmer-than-normal surface waters in the equatorial Pacific shifts the atmospheric circulation, and as a result, brings the Pacific jet stream over the southern U.S.
This shift in the Pacific jet stream tends to bring cooler and wetter weather to the southern U.S., and drier and warmer weather to the north.
El Niños typically last 9-12 months, beginning in the spring and peaking in the late fall or winter. Although El Niños are generally shorter than 12 months and, by comparison, shorter than La Niñas. The longest El Niño on record ran 18 months while the strongest El Niño ever recorded is said to be the El Niño of 1982-1983.
History
The El Niño Southern Oscillation (ENSO) is a naturally-occurring Earth process that has been occurring for thousands of years. It’s characterized by an El Niño (warmer), La Niña (colder) and a neutral phase of equatorial Pacific waters. Not until the 1950s did scientists begin studying and recording the “sloshing” of the warmer waters along the equator in the Pacific basin. Since then, approximately 20 El Niño events have been recorded.
Courtesy: Midwestern Regional Climate Center
NOTE: the graph above does not include a weak El Niño observed in 2018-2019
Courtesy: NOAA Physical Science Laboratory
The warmer the sea surface temperatures are above normal determines the strength of an El Niño event. Of all the El Niño events recorded, half are said to have been moderate to strong.
Impacts
El Niño events are typically correlated with:
- Warmer annual global temperatures
- Increased tropical activity in the eastern Pacific basin
- Decreased tropical activity in the Atlantic basin
- Warmer and drier conditions in northern U.S. and Canadian winters
- Cooler and wetter conditions in southern U.S. winters
- Increased coral bleaching in the Pacific
- More storms in the winter for the southern U.S. (due to the position of the jet stream)
- Less spring tornado and hail events for Central & South Plains in spring
Courtesy: NOAA
Courtesy: NOAA, based on originals by Gerry Bell
El Niño in Central Texas
One glaring correlation between Central Texas and past El Niños is the occurrence of destructive floods. The Llano River Flood (2018), the Memorial Day Flood (2015), and the October 1998 Flood all occurred in El Niño years. The cause of each flood differs, although, many involve Pacific hurricane remnants, in line with above-average Pacific hurricane activity typically seen during El Niño years.
More broadly, warmer ocean temperatures in the Pacific add more heat and fuel to developing storms, tropical or not. If those storms get carried in Texas’ direction, they can, and often do, bring heavy rainfall.
Although an El Niño event typically favors wetter and cooler conditions in our area during the late fall and winter, every El Niño is different, and it is impossible to know or forecast a major weather event months in advance.
