La Nina is likely to cool the tropical Pacific in coming months, a phenomenon which usually causes stronger monsoons across Asia and eastern Australia, the World Meteorological Organisation (WMO) said on July 06. The weather condition also promotes the development of storms including hurricanes in the tropical Atlantic, it said.
El Nino, the opposite phenomenon which warms the sea, rapidly dissipated in early May after prevailing since late 2009. This has led to the current situation, bordering on a weak La Nina event in the tropical Pacific, according to the United Nations agency. "These borderline conditions are more likely than not to strengthen to become a basin-wide La Nina episode during the second half of 2010," WMO said in a statement.
"While it is likely that the La Nina conditions will further develop over the next several months, the timing and magnitude of such an event in 2010 are still uncertain," WMO expert Rupa Kumar Kolli told a news briefing in Geneva.
Current conditions are not adequate for the WMO to declare that a La Nina event is actually in place, he said.
Most forecasting models do not a indicate a particularly strong La Nina event in terms of sea-surface temperatures, he said. Typical La Nina events are usually associated with stronger monsoons in most parts of Asia and also Australia. A La Nina event is also associated with an active hurricane season in the tropical Atlantic, Kolli said.
"So these are some of the risk factors that should be kept in mind," he said. The U.S. government's top weather agency has already predicted that the Atlantic storm season which began on June 1 may be the most intense since 2005 when Hurricane Katrina killed over 1,000 people and disrupted oil production by crashing through Gulf of Mexico energy facilities. Kolli, asked about the possible effects of La Nina on efforts to clean up BP's Gulf of Mexico oil slick, said: "La Nina by itself is unlikely to play a role in that region."
"But considering that there is a possibility of an active hurricane season, the hurricanes definitely have the potential to churn up the sea and also play a role in the spread of the oil spill in some ways. But this all depends upon the track of the hurricane and the strength of the hurricane and many other factors associated with individual hurricane events," he said.
If a La Nina event becomes well-established, it is also associated with a slight decrease in air temperature in many parts of the world, according to Kolli. "That has implications for the global mean temperature," he told Reuters.
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