El Nino 2002: How big a punch?

Heavy flooding in Peru in early February is one sign of a coming El Nino.

(CNN) -- "El Nino" has arrived.

Scientists at the U.S. National Oceanic and Atmospheric Administration, or NOAA, report that surface temperatures of the Pacific Ocean near the South American coast warmed 4 degrees Fahrenheit (2 degrees Celsius) in February. That is a strong sign that the Pacific is headed for an El Nino condition that could last more than a year.

"It's still too early to determine the potential strength of this El Nino or exactly what weather conditions it will bring to the United States, but it is likely these warming conditions in the tropical Pacific will continue until early 2003," said NOAA Administrator Conrad Lautenbacher in a statement.

VIDEO CNN's Ann Kellan reports on the possible weather effects of an upcoming El Nino (March 7) Play video (QuickTime, Real or Windows Media)   EXTRA INFORMATION Notable effects attributed to El Nino in 1997-98    RESOURCES Fact Sheet: Charting El Nino

One sign of a coming El Nino is a change in what fish can be found off the west coast of South America. Peruvian officials report that cold water anchovies have recently been replaced by tropical species.

Peruvian fishermen are credited with recognizing and naming this climate phenomenon in the 19th century. They first noticed the annual southerly flow of warm equatorial waters around Christmas, giving it the name El Nino, Spanish for "the Christ Child."

The warmer waters usually meant bad news for fishermen and for birds -- fewer cold-water fish in the region.

Another effect of the warming Pacific waters is the serious flooding in Peru over the past several weeks.

Lautenbacher, a retired U.S. Navy vice admiral, told CNN the impact of an El Nino can be dramatic.

A network of buoys across the Pacific monitors temperature changes.

"It makes a big difference to our economy to know what's about to happen in terms of energy resources, in terms of fishing industry, agriculture, what kinds of crops you are going to plant," he said.

NOAA scientists now study ocean changes with polar-orbit satellites and 70 buoys moored across the equatorial Pacific that provide real time atmospheric and oceanographic data.

Each month forecasters update their predictions on how El Nino will affect different parts of the world.

The U.S. government dramatically increased its monitoring capabilities after the El Nino of 1982-83 caught many parts of the country by surprise. Storms that hit California were particularly severe.

Map of 2002-2003 El Nino predictions

A particularly potent El Nino in 1997-98 led to sometimes bizarre weather conditions around the globe, from balmy winter temperatures in the often frigid U.S. midwest to severe droughts and wildfires in Indonesia.

Although scientists have not yet made specific regional forecasts, NOAA said typical El Nino effects on the United States include:

El Nino usually occurs once or twice a decade and usually, but not always, is followed by La Nina, during which colder than average water replaces warm and the weather effects are the reverse of El Nino.