El Nino -- the warming of surface temperatures in the central and eastern equatorial Pacific ocean, which can influence the formation of Atlantic hurricanes -- has arrived, scientists at the National Oceanic and Atmospheric Administration (NOAA) said Thursday.

At the end of June eastern equatorial Pacific sea surface temperatures were at least one degree centigrade above average, NOAA said.

El Nino events, which occur every two to five years and typically last about 12 months, can help suppress Atlantic hurricane activity.

The National Weather Service's National Hurricane Center has reported no tropical cyclones in the Atlantic basin this year. The consensus forecast has been for a relatively mild hurricane season.

Some forecasters, including Andover, MA-based WSI Corp., have said a new El Nino event, combined with cooler Atlantic ocean temperatures, is likely to make the 2009 Atlantic hurricane season "relatively quiet" (see NGI, June 29). Other forecasters calling for a relatively mild hurricane season include Colorado State University (see NGI, June 8), NOAA (see NGI, May 25) and AccuWeather.com Chief Long Range Forecaster Joe Bastardi (see NGI, May 18).

El Nino's impacts depend on a variety of factors, including intensity and extent of ocean warming, NOAA said.

In addition to suppressing Atlantic hurricane formation, El Nino events can increase storminess across the South, produce winter storms in California and the Southwest, and create less wintry weather across the North.

The latest El Nino is expected to continue developing over the next several months and last through the coming winter, NOAA said.

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