An El Nino watch has been issued by the U.S. Climate Prediction Center, warning of the possible development of the weather-altering event that can bring rain to California and South America and raise winter temperatures in the U.S. Northeast and Midwest.
There’s a 52 percent chance that the Pacific Ocean will warm enough to trigger an El Nino late this summer or in early fall, said Michelle L’Heureux, a climate scientist at the Climate Prediction Center in College Park, Maryland.
"We have increased our probabilities, not a whole lot, but just enough that we feel we need to start drawing attention to the situation," L’Heureux said in an interview. "There are still dominoes that have to fall here. This is not a guarantee, but certainly we’re issuing this watch so folks have a heads- up."
Rubber, sugar, coffee, and natural gas are among the commodities that can fluctuate because of an El Nino, which usually occurs every three to five years and can last months. The phenomenon often touches off warmer winters across the northern U.S., heavier rains from southern Brazil to Argentina and drier conditions across southeast Asia and Indonesia. It also can lead to a calmer Atlantic hurricane season and a stormier winter in the U.S. South.
An El Nino in 1982-83 caused $8.1 billion in damage worldwide and prompted efforts to better monitor the ocean warming, according to the National Oceanic & Atmospheric Administration.
"On the precipitation side of it, you can have a more active winter storm track coming into California, and if you get a strong mode then you get a real good storm track coming across the southern U.S., too," said Joel Widenor, a meteorologist at Commodity Weather Group LLC in Bethesda, Maryland.
California is currently in the grips of a drought that has left reservoirs dry.
The Australian Bureau of Meteorology noted the warming trend in the Pacific last month. An El Nino means less rain across eastern Australia through June to November, the bureau said.
The last El Nino occurred in 2009 to 2010, and since then the other two phases of the cycle, a cooling called La Nina and a period of neutral conditions, have held sway, the climate center said.
The decision to issue the watch came because the waters under the Pacific’s surface have grown warmer in the last several weeks. Winds pile up warm water in the western Pacific and then it sloshes back beneath the surface toward the east and the coast of South America. This is called a Kelvin Wave, L’Heureux said.
"Kelvin Waves are a necessary condition for El Nino but they’re not necessarily sufficient, meaning we have still yet to see what sort of impact this will have," she said.
There is more to an El Nino than just water temperature, she said. The ocean warming has to be tied to changes in the atmosphere, which set off the global shifts in weather patterns. The entire process is referred to as the El Nino Southern Oscillation, or ENSO.
Many of the impacts of an El Nino depend on its strength, and L’Heureux said predictions of intensity are harder to make. It may be June or July before researchers get an idea.
There is also a possibility the pattern won’t develop at all, she said. In 2012, the Pacific began to warm, while the atmosphere above the ocean failed to respond. The El Nino didn’t occur.
Predictions can go awry because of the "spring barrier," the time between March and May when computer models often have trouble making sense of what is happening in the Pacific, L’Heureux said.
During the last El Nino, 12.6 inches (32 centimeters) of snow fell on Dallas in February 2010 and 32.1 inches at Washington’s Reagan National Airport, according to National Weather Service records. Temperatures were 1.7 degrees higher than normal in Boston and 6 degrees higher in Portland, Maine, that month.
El Nino can also increase wind shear across the tropical Atlantic during the June to November hurricane season, reducing the chances of a devastating storm. The Gulf of Mexico is home to about 6 percent of U.S. natural gas output, 23 percent of oil production and more than 40 percent of petroleum refining capacity. The 2009 season was the quietest in a decade.