Strong El Nino underway
Published 7:00 am Tuesday, August 4, 2015
Meteorologists and oceanographers have been closely watching upper ocean temperatures climb above normal in the central and eastern tropical Pacific Ocean over the past several months. El Nino is underway, and last week forecasters with the National Oceanic Atmospheric and Oceanic Administration said there is a greater than 90 percent chance it will continue through the summer, fall, and winter.
That almost certainly means fewer hurricanes in the Atlantic and Gulf of Mexico this season, and probably a wetter than normal November-March for us.
El Nino, more properly spelled with the Spanish tilde (a wavy line) over the n, and pronounced “el NEEN-yo,” is literally translated “the male child,” and when capitalized traditionally refers to the Christ Child.
What does that have to do with sea surface temperatures in the tropical Pacific?
The Pacific waters offshore of the South American nation of Peru are abundant fisheries. This is because for most of the year, winds blowing southward parallel to the coast cause cool, nutrient-rich waters to rise to the surface, a phenomenon known as upwelling. The entire food chain benefits, and there is an abundance of fish. Peruvian fishermen have made their living working these waters for hundreds of years. Commercial fishing for anchovies became a major industry in Peru in the 1950s.
Typically in December and January, the upwelling weakens, upper ocean temperatures warm, and there are fewer fish. The fishermen take a break. Because this usually happens around Christmas, they call this phenomena El Nino, referencing the Christ Child.
Normally by February and March the cool upwelling begins to return, and so do the fish.
But, occasionally, something different happens. Warmer than normal sea surface temperatures persist offshore of the Peru coast right on through the next year. Heavy rains fall on the normally arid Peruvian coastal lands.
When that happens it’s because something is happening on a much bigger scale. An event is unfolding that originates thousands of miles to the west in the central and western tropical Pacific. The normal easterly trade winds there have weakened and bursts of winds from the west have pushed the waters of the upper ocean back toward South America. Pulses of ocean energy known as Kelvin waves move east along the equator. Most of the energy of these waves is underwater. When after a couple of months these waves reach the South American coast, the ocean’s surface waters near the coast are pushed downward and replaced by the warmer offshore surface waters.
Over the ensuing months warmer than normal sea surface temperatures spread over much of the eastern Pacific, including off the west coast of North America. Weather patterns are disrupted over much of the globe as the atmosphere responds. This can go on for a year.
The stronger the El Nino as measured by warm sea surface temperatures in the eastern tropical Pacific, the more dramatic and far-reaching the weather is impacted. There have been 12 moderate to strong El Ninos during the past 65 years. This El Nino is shaping up to be one of the two or three strongest, and certainly the strongest since 1997-98.
Stay tuned – you’re going to hear a lot more about El Nino over the next nine months.
By Skip Rigney