May 16th, 2015-
WeatherBug– El Nino, the above-average warming of the equatorial Pacific Ocean, has been in place since last fall and has recently strengthened as we have moved through spring. The question as to whether it would continue has now started to shift to: How will it alter the weather patterns in the U.S., as well as the rest of the world?
The El Nino phenomenon, which last occurred in 2009-2010, 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 nine to 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.
The Caribbean Sea experiences a warm and dry summer.
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 during the winter months.
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.
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 patterns.
Japan and the Korean Peninsula experience warmer El Nino winters.
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. –WeatherBug
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.