The Niño
What does the temperature of seawater in the tropical Pacific have to do with weather in the Florida Keys? It turns out – quite a bit.El Niño is a term you may have seen or heard this year amid the din of television and radio news, or via social media. What does it mean? And, what does it mean for the Florida Keys fishing, diving, and boating community? You may be interested to know that the term itself, “El Niño”, originated among the Spanish-speaking fishermen of northern Peru. The term was applied initially to a warm annual southward coastal current that developed shortly after the Christmas season (El Niño being the Spanish name referring to “the Christ Child”). Eventually, the term became more commonly used to refer to the occasional very strong coastal warmings that were associated with torrential rains in the desert coastal regions of both northern Peru and southern Ecuador. The current meteorological definition of El Niño developed following the discovery that the Peruvian and Ecuadorian coastal warmings were part of a global-scale phenomenon arising from ocean-atmosphere interactions across a broad expanse of the equatorial Pacific Ocean. According to the Glossary of Meteorology, the meteorological “El Niño” is a “significant increase in sea surface temperature over the eastern and central equatorial Pacific that occurs at irregular intervals, generally ranging between two and seven years”. The phenomenon known as “La Niña” is the counterpart to “El Niño”, and refers to a significant decrease in sea surface temperature over roughly the same part of the eastern and central equatorial Pacific. So, what does the temperature of seawater in the tropical Pacific have to do with weather in the Florida Keys? It turns out – quite a bit, actually. First, during an El Niño, the upper layers of most of the central and eastern tropical Pacific Ocean are warmer than average by several degrees Fahrenheit. The very large expanse of warm ocean water leads to below-average atmospheric pressure at the surface and a thicker, warmer atmosphere above, over a very large region. In addition, shower and thunderstorm activity increases markedly, resulting in a spike in the infusion of heat and momentum into the atmosphere over the eastern tropical Pacific Ocean. These developments, in turn, have important consequences for weather and climate around the globe. One result is that the strongest portion of the North Pacific jet stream tends to shift eastward, and buckle southward, bringing the mean winter storm track southward over the southern United States and Gulf of Mexico. The impacts of such a shift include cloudier, wetter, stormier, and cooler weather during the winter months (December, January, and February) in the Florida Keys (on average). El Niño episodes vary with respect to intensity, with the stronger episodes associated with a higher number of cloudy, wet days during winter in the Keys. Two of the strongest El Niño events from the last 40 years include those from 1982–1983 and 1997–1998. The El Niño which developed in 2015 likely will be on par with these events, according to the NOAA Climate Prediction Center. For additional information, visit the “NOAA El Niño Portal” at elnino.noaa.gov. And, for the latest forecasts going out seven days in the Florida Keys, be sure to visit the Florida Keys National Weather Service home page at weather.gov/key. As the 2015–2016 El Niño peaks this winter, remember to check the weather before heading out on the water, and as always, be weather-ready, and stay safe!
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