Most weather enthusiasts, heck, most people walking on a city sidewalk have heard of El Niño. They might know some details, at least the fact that it is a weather phenominon–maybe even that it is an ocean current. And then they blame everything on El Niño.

La Niña is less well known, but she gets around. And boaters need to be mindful of both her and her more popular brother because they affect temperature, winds and precipitation. Depending on where you are and which event is unfolding, seafaring conditions may be better–or much worse.

El Niño and La Niña are disruptions of the normal ocean currents and atmospheric winds in the tropical Pacific Ocean that have global climate implications. El Niño and La Niña events typically last 12 months, beginning in the summer and peaking during the winter and spring.

NOAAEl Niño's typical seasonal impacts.

SHE'S HERE

Moderate La Niña conditions are right now occurring in the tropical Pacific Ocean and are expected to continue into next year. Details of current weather conditions can be found at the National Weather Service (NWS) Climate Prediction Center website (see link).

It is the typical warm and dry conditions found in the southern U.S. during a La Niña event that will likely create great boating opportunities this winter in the Gulf of Mexico and off the southeastern coast.

Stormy conditions can be expected in the Pacific Northwest. And in the eastern tropical Pacific, the colder deep waters that rise to the surface bring nutrients and increased aquatic activity. That's why fishermen typically love the onset of La Niña.

But the biggest effect of El Niño and La Niña events is their impact on the Atlantic hurricane season. El Niño inhibits the formation of hurricanes, while La Niña promotes greater than average hurricane seasons. The current La Niña event may impact the 2008 hurricane season by causing greater hurricane activity.

DISRUPTIVE EVENTS

The name El Niño means "The Little Boy" or "Christ Child" in Spanish. Fishermen off the Pacific coast of South America first used it to describe the unusually warm water that would form there around Christmas every three to five years. During an El Niño, ocean temperatures in the eastern tropical Pacific Ocean rise above average, while surface winds blowing east to west relax or may even blow in the opposite direction.

The term La Niña was used to indicate opposite conditions. During a La Niña, also called a cold episode, ocean temperatures fall below average and winds blow stronger from east to west in the tropical Pacific.

Both El Niño and La Niña are important because they impact the global climate system, not just locally in the tropical Pacific. Both conditions highly influence long-range temperature and precipitation forecasts for the U.S. and adjacent waters, especially during the winter months when the intensity is greatest.

THE CAUSES

El Niño and La Niña conditions involve the interactions between ocean currents and atmospheric winds. Atmospheric scientists describe them as “chicken and egg” scenarios, unsure if the initial changes in ocean currents affect the winds or the other way around.

Here's how the process works: Ocean temperatures in the eastern tropical Pacific depend on the amount of upwelling. Upwelling is the rise of deeper colder water to the surface when winds push the warmer surface waters away from the coastline. Because the prevailing winds off the coast of South America in the Pacific blow from east to west, surface water is pushed westward, allowing the colder deeper water to rise to the surface. During an El Niño, surface winds relax or sometimes reverse direction and blow from west to east, shutting down the upwelling process. When upwelling stops, surface ocean temperatures increase.NOAALa Niña's typical seasonal Impacts.

La Niña conditions again are opposite. Winds blow harder from east to west, increasing the upwelling process. This causes ocean temperatures to decrease below what is typical. The push of water from east to west is actually observed by satellites as a rise in sea level in the western Pacific.

The initial causes of El Niño and La Niña remain unclear to scientists. Buoys positioned throughout the tropical Pacific help provide critical ocean temperature, atmospheric pressure, and wind observations. These indicators help pinpoint the onset of an El Niño or La Niña event. Predicting their strength is more challenging, and long-term forecasting of these events remains beyond the capacity of current science.

WEATHER IMPACTS

Global impacts during El Niño and La Niña episodes are illustrated in accompanying figures. The two maps show typical conditions during the Northern Hemisphere winter and summer months. Notice that the effect on the U.S. climate is much more profound in the winter months because the intensity is greater. By studying previous El Niño and La Niña events, scientists have identified temperature and precipitation anomaly patterns that are consistent from one event to another.

For El Niño events, the southern U.S. commonly experiences cooler and wetter winters, while Alaska, western Canada, and the northern plains are warmer than normal.

Southern California has been hit hard by strong storms during the El Niño years of 1982–83 and 1997–98, causing flooding and mudslides. During El Niño events, ski resorts in the Rockies and New England have had to shut down during winter months due to warmer temperatures and a lack of snow.

For La Niña events during the winter months, western Canada and Alaska are typically colder than normal. This arctic air can periodically penetrate into the northern Plains region of the U.S., bringing much colder temperatures with it. Other regions in the United States can expect atypical conditions as well.

Throughout the southern half of the U.S., the weather during La Niña becomes warmer and drier than average. This may exacerbate the already devastating drought in the Southeast and Southwest. La Niña conditions also include above average precipitation in the Northwest and Midwest regions. During the La Niña of 1999 a world record snowfall for one season was measured in the North Cascade mountain range of Washington State.