Another active hurricane season forecast

The very active 2010 Atlantic Basin hurricane season just ended last week and there is already a prediction for a highly active 2011 hurricane season.

Colorado State University scientists Philip Klotzbach and William Gray’s extended range forecast issued Wednesday predicts 17 named storms, nine hurricanes and five major hurricanes, all figures that are significantly higher than the historical average.

The busy hurricane season is predicted mainly because the duo believes a La Niña or El Niño neutral condition will exist during the 2011 hurricane season, which runs from 1 June through 30 November. El Niño is a cyclical warming of the sea surface temperatures in the tropical Pacific Ocean that is known to cause higher wind shears, which inhibit tropical cyclone formation in the Atlantic Basin. Conversely, La Niña is a cyclical cooling of the sea surface temperatures in the tropical Pacific Ocean known to cause conditions conducive to tropical cyclone formation and strengthening in the Atlantic Basin.

“One of the important questions for the upcoming hurricane season is whether El Niño will re-develop for the 2011 hurricane season. At this point, we think that this is a very unlikely scenario, given the current upper ocean heat content structure across the tropical Pacific,” the report issued by Klotzbach and Gray stated.

“We do not expect to see El Niño conditions reemerge in 2011. At this point, we are uncertain whether La Niña conditions or neutral conditions are more likely for the 2011 hurricane season.”

The Colorado State scientists were not the only ones to forecast a busy 2011 hurricane season this week. Tropical Storm Risk issued its extended range forecast on Monday, predicting 15.6 named storms, 8.4 hurricanes and four major hurricanes of Category 3 strength or higher. Similar to Klotzbach and Gray, Tropical Storm Risk believes that a weak La Niña will cause weaker than normal upper level trade winds in the Atlantic Basin. This factor, when combined with predicted warmer-than-average sea surface temperatures in the tropical Atlantic Ocean and Caribbean Sea, will make those areas more prone to tropical cyclone activity.

Tropical Storm Risk discussed the forecast skill of their extended hurricane season outlooks in the report it issued Monday.

“It is clear that the skill of the extended range hurricane forecasts issued in early December, while positive, is low,” it stated. “Skill climbs slowly as the hurricane season approaches. Moderate skill levels are achieved in early June and good skill levels in early August.”

Klotzbach and Gray actually significantly underestimated the number of named storms and hurricanes in the 2010 hurricane season in their extended range forecast issued 9 December, 2009. Their 7 April, 2010, forecast continued to underestimate tropical cyclone activity in the 2010 season. However, its 2 June, 2010, forecast – issued the day after the hurricane season started – came very close to accurately predicting the actually numbers of named storms and hurricanes during the 2010 season and correctly predicted five major hurricanes.

The US National Oceanic and Atmospheric Administration, the organisation that runs the National Hurricane Center in Miami, does not issue a hurricane season forecast until late May.

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