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El Nino's Effects Are Felt Worldwide

August 2009

By WeatherBug's Stephen Baxter

El Nino, the above-average warming of the equatorial Pacific Ocean, is developing and will alter weather patterns and change temperature and precipitation trends in many parts of the world, including the U.S.

The El Nino pattern, which last occurred in 2006, is the warm phase of the El Nino/Southern Oscillation (ENSO), the periodic changes in atmospheric pressure and ocean temperatures in the tropical Pacific. Usually forming every two to five years and lasting about 12 months, El Nino conditions are characterized by changes in the easterly trade winds that, in turn, affect weather patterns both inside and outside the tropics.

North America

  • Mild winters from Alaska through western Canada into the northern U.S. are common.

  • An active southern jet stream brings wet and cool weather to the southern U.S. from California to the Southeast.
  • The Caribbean Sea experiences a warm and dry summer.
  • South America/Eastern Tropical Pacific

    • Warm ocean waters and lower atmospheric pressure lead to increased precipitation and warmer temperatures from the central Pacific to the equatorial coast of South America, where serious flooding can occur. Just north of this region, Hawaii tends to have dry, drought-prone winters.

  • Weaker trade winds reduce upwelling of nutrient-rich deep ocean water off the South American coast. This can have devastating effects on major fishing industries, especially during strong and long-lasting El Nino`s. The strong 1997-98 episode cost Peru $3.5 billion in economic losses as fishery exports dropped 76 percent.
  • Warmer and drier weather is likely in east-central South America, including Brazil, which can negatively impact agricultural industry and increase forest fires.
  • Asia/Western Tropical Pacific

    • Higher than normal pressure tends to decrease rain in the far western equatorial Pacific and Southeast Asian countries like Indonesia. Drought can be a major threat during prolonged El Nino events.

  • The rainy summer monsoon in India tends to be drier during El Nino seasons.
  • Japan and the Korean Peninsula experience warmer El Nino winters.
  • Australia

    • Drier conditions can be expected year-round in northern Australia, where drought is a major concern.

  • Southeast Australia typically sees warmer than normal El Nino summers.
  • Other than these effects on global weather, El Nino also influences tropical cyclone development around the world. The Atlantic hurricane season is known to have decreased activity during El Nino due to increased upper-level winds that tear storms apart. Tropical cyclones in the West Pacific, both in the Northern and Southern Hemispheres, tend to develop farther east. This reduces the hurricane threat in the Marianas Islands including Guam, but increases the number of tropical cyclones near Tahiti.

    Stay tuned to WeatherBug for more information on the current El Nino and how it will affect weather both in the U.S. and abroad.

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