The 2008 hurricane season was one of the most active on record. In this image, taken on Aug. 28, 2008, three storms can be seen in various stages: Fay, Gustav and Hannah. (National Oceanic and Atmospheric Administration)U.S. government scientists say El Niño, the periodic warming of water in the tropical Pacific Ocean that can influence weather around the world, has returned.

The Pacific had been in what is called a neutral state, but forecasters at the National Oceanic and Atmospheric Administration say the sea surface temperature climbed to 1.8 degrees Fahrenheit above normal along a narrow band in the eastern equatorial Pacific in June.

In addition, NOAA's Climate Prediction Center said temperatures in other tropical regions are also above normal, with warmer than usual readings as much as 975 feet (297 metres) below the ocean surface.

In general, El Niño conditions are associated with increased rainfall across the east-central and eastern Pacific and with drier than normal conditions over northern Australia, Indonesia and the Philippines.

A summer El Niño can lead to wetter than normal conditions in the intermountain regions of the United States and over central Chile. In an El Niño year, there tend to be more Eastern Pacific hurricanes and fewer Atlantic hurricanes.

The forecasters said they expect this El Niño to continue strengthening over the next few months and to last through the winter of 2009-2010.

"Advanced climate science allows us to alert industries, governments and emergency managers about the weather conditions El Niño may bring so these can be factored into decision-making and ultimately protect life, property and the economy," NOAA Administrator Jane Lubchenco said in a statement.

Hurricane frequency affected

NOAA officials noted that not all El Niño effects are negative. For example, it can suppress Atlantic hurricanes and bring needed moisture to the arid southwest.

But it can also steer damaging winter storms to California and increase storminess across the southern United States.

The warming of the ocean can also lead to a reduction in the seafood catch off the West Coast, and fewer fish can also impact food sources for several types of birds and marine mammals.

A recent study by researchers at Georgia Tech suggests there may actually be two forms of El Niño, depending on whether the warming is stronger in the eastern or central pacific.

While the current warming seems to be strongest in the east, the more traditional form, government forecasters did not categorize it.

If the Georgia Tech study is correct, this would be the type of El Niño that reduces hurricanes in the Atlantic and Caribbean. The other form, centered farther west, reportedly seems to promote Atlantic storms.