El Nino on the way

Sstjune11 2014

There have been many stories in the news recently concerning the El Nino phenomenon. This is mainly because it appears quite likely that a significant El Nino event will take shape in the coming months and persist for up to a year. With this in mind, it is worth taking a look at what this might mean for those planning ocean voyages during this period of time.

First, though, it’s worth running through a very basic review of what El Nino is. The phenomenon has been present for centuries, but received its name in the late 19th century because it was noticed that along the northern portion of the west coast of South America sea surface temperatures turned noticeably warmer periodically and that when this warming occurred, it tended to occur late in the year. The name “El Nino” means “the child” and since the phenomenon occurred around Christmas time, the name was connected with the celebration of Christ’s birth.

The warming of the waters in this area had significant impacts on the fisheries, typically leading to diminished catches of native species which depend on the upwelling of colder water. During an El Nino event, the cold water upwelling is diminished, and with it the supply of nutrients that it carries, thus leading to a reduction in the fishery.

In the second half of the 20th century when more comprehensive observations of the atmosphere and the ocean became available, especially as satellite measurements became possible, it was determined that the El Nino phenomenon was much more widespread than just the waters off northern South America. In fact, the anomalously warmer waters extended over a good portion of the equatorial Pacific. In a non-El Nino year, sea surface temperatures are warmest in the western tropical Pacific. During an El Nino episode the warmer sea surface temperatures spread east through the central and eastern Pacific, and during particularly strong El Nino years, can reach the northern coast of South America.

More research into the phenomenon has revealed that the warming sea surface temperatures are connected with other large scale changes in the atmosphere, including changes in average surface pressures over portions of the Pacific, which, in turn, lead to changes in wind patterns. Also, the effects of the phenomenon are not limited to the equatorial Pacific, but rather stretch around the globe. The research has also led to the ability to forecast El Nino, and forecasters who specialize in this type of prediction are indicating the high likelihood of a significant event later this year into next year.

This brings us back to our original question: How will this affect ocean voyagers?

One of the biggest concerns is tropical storm and hurricane formation. During an El Nino episode, tropical cyclone activity in the North Atlantic basin tends to be diminished. This is due to shifts in the wind patterns which lead to stronger upper level winds in tropical latitudes, and these are not conducive to storm development. This could mean easier passages for voyagers who need to move through parts of the Atlantic where tropical storms and hurricanes could occur. On the Pacific side, though, the warmer waters spreading farther east typically will allow for an increase in tropical cyclone activity. This is particularly noticeable in the South Pacific as during their tropical season (December through March) storms have the potential to track much farther east into French Polynesia than in a non-El Nino year. This could mean a bigger threat for those contemplating a crossing from Panama toward Australia or New Zealand.

There are changes in the prevailing wind patterns in the tropical Pacific during an El Nino event as well. The typical easterly trade winds will tend to be a bit weaker, particularly closer to the equator and in more western portions of the Pacific. There can be periods of time where the winds become light and variable, and perhaps even acquire a westerly component for limited time periods. For those traversing these regions under sail, this can mean that the trade winds will be a bit less reliable than normal, and also that the wind speeds may not be as high which may mean reduced boat speed. Farther away from the equator the effect may not be as significant.

Changes in the jet stream configurations occur in subtropical and lower temperate latitudes as well, and these changes can produce stronger storms in the central and eastern North Pacific during an El Nino episode. This could lead to more frequent periods of strong winds and high seas in the coastal waters of the western U.S., and perhaps reduced opportunities for favorable windows for coastal passages. Similarly, there tend to be stronger storms in the Gulf of Mexico and in the Atlantic coastal waters of the southeastern U.S., particularly during the winter season, and this may reduce passage opportunities in these areas.

While the effects of El Nino that have been mentioned are reasonably well documented in the historical record, one must keep in mind that every El Nino episode is different in strength and in scope, and therefore the impacts of the episodes will be different in terms of magnitude, frequency, and in fact, whether they occur at all in any given event. Also, because the effects are measured and averaged over an entire season, this means that there will be some parts of the season where the effects are not as significant. For example, even though there tends to be more storminess in the fall, winter and spring in the eastern North Pacific, this does not mean that conditions for every day of the season would be poor for a passage from San Francisco to San Diego. Also, even though Atlantic hurricane activity is usually diminished during an El Nino episode, it does not mean that no hurricanes will occur, and in fact storms could still affect popular cruising areas.

This newsletter has barely scraped the surface of El Nino, both in terms of its description, and its impacts. For much more information, NOAA hosts a website with comprehensive information about the phenomenon. Here is the link: www.elnino.noaa.gov

By Ocean Navigator