MIAMI, FLORIDA (BNO NEWS) -- Despite an unusually early start to the Atlantic and Eastern Pacific hurricane seasons, forecasters at the U.S. National Oceanic and Atmospheric Administration (NOAA) expect a near-normal season with nine to fifteen named storms in the Atlantic and twelve to eighteen named storms in the East Pacific, according to figures released on Thursday.
NOAA's Climate Prediction Center said climate patterns similar to those expected this year have historically produced a wide range of activity, but experts estimate a 50 percent chance of a near-normal season for both the Atlantic and the Eastern Pacific basins. Forecasters expect a below-normal hurricane season in the Central Pacific basin.
The Eastern Pacific hurricane season got off to an early start this year, with Tropical Storm Aletta forming far off Mexico's Pacific coast several hours before the season was officially due to start on May 15. The storm dissipated days later without impacting any land, but Hurricane Bud has since formed and is currently aiming for Mexico's Pacific coast as a Category 2 storm.
In the Atlantic basin, where the season officially begins next month, Tropical Storm Alberto formed off the U.S. state of South Carolina late last week, making it the earliest-forming tropical storm in the Atlantic basin since Ana in 2003. The storm dissipated days later without causing much trouble, but it was the first time on record that a tropical storm formed before the official start of the hurricane season in both the Atlantic and East Pacific basins.
But despite the unusually early start, forecasters expect a relatively quiet hurricane season. The outlook for the Atlantic basin calls for nine to fifteen named storms, with four to eight becoming hurricanes and one to three expected to become a major hurricane (category 3 or higher). They estimate only a 25 percent chance of an above-normal season and a 25 percent chance of a below-normal season.
An average Atlantic hurricane season produces eleven named storms, with six becoming hurricanes and two becoming major hurricanes. The Atlantic hurricane season runs from June 1 through November 30, with peak activity in September.
"Regardless of the outlook, it's vital for anyone living or vacationing in hurricane-prone locations to be prepared. We have a stark reminder this year with the 20th anniversary of Hurricane Andrew," said NOAA Administrator Jane Lubchenco. Andrew was a major Category 5 hurricane which devastated South Florida in August 1992, killing 26 people and causing more than $26.5 billion in damage, despite a season which produced only six named storms.
Favoring storm development in the Atlantic basin this year is the continuation of the overall conditions associated with the Atlantic high-activity era that began in 1995, in addition to near-average sea surface temperatures across much of the tropical Atlantic Ocean and Caribbean Sea, known as the Main Development Region. Favors now in place that could limit storm development, if they persist, is cooler seas surface temperatures in the far eastern Atlantic and strong wind shear which is hostile to hurricane formation in the Main Development Region.
“Another potentially competing climate factor would be El Niño if it develops by late summer to early fall," said Gerry Bell, lead seasonal hurricane forecaster at the Climate Prediction Center. "In that case, conditions could be less conducive for hurricane formation and intensification during the peak months of the season, possibly shifting the activity toward the lower end of the predicted range."
Last year, the Climate Prediction Center's outlook called for an above-normal hurricane season in the Atlantic basin with twelve to eighteen named storms, with six to ten becoming hurricanes and three to six becoming major hurricanes. The actual season ended with eighteen named storms of which seven became hurricanes and four became major hurricanes. A post-season review identified a nineteenth storm which forecasters failed to observe at the time.
In the Eastern Pacific, forecasters expect a near-normal season with twelve to eighteen named storms, with five to nine becoming hurricanes and two to five becoming major hurricanes. The outlook indicates a 50 percent chance of a near-normal season, a 30 percent chance of a below-normal season, and a 20 percent chance of an above-normal season.
An average Eastern Pacific hurricane season produces fifteen to sixteen named storms, with eight to nine becoming hurricanes and four becoming major hurricanes. The Eastern Pacific hurricane season runs from May 15 through November 30, with peak activity from July through September.
"The eastern Pacific has gotten off to a busy and early start of the season, with Tropical Storm Aletta last week and Hurricane Bud churning off the Mexican coast this week," Bell said. "NOAA's seasonal hurricane outlook gives people an idea of how the season will likely unfold so they will be prepared and equipped to respond when disaster strikes. Despite our predictions, it only takes one hurricane to cause a lot of damage and loss of life if people aren't prepared."
The outlook is based on the analysis and prediction of two competing climate signals. The first is a continuation of conditions that have reduced hurricane activity in the Eastern Pacific basin since 1995. But expected to offset this signal is above-average sea-surface temperatures in the eastern tropical Pacific Ocean, with the possible development of El Niño later in the season. Warmer waters in the eastern Pacific can produce decreased vertical wind shear and increased hurricane activity in the eastern Pacific hurricane region.
Associated with the climate conditions that have contributed to this reduction in eastern Pacific hurricane activity, the Pacific Inter-Tropical Convergence Zone (ITCZ) has shifted farther to the north, allowing for extensive southwesterly flow into the eastern tropical North Pacific. Also, the upper-level ridge over Mexico has been stronger than average, resulting in enhanced upper-level easterly winds. This combination of factors leads to increased vertical wind shear, which typically limits the number, intensity, and duration of the tropical storms and hurricanes. These storms also tend to form closer to Mexico and closer to cooler ocean temperatures, both of which limit their duration.
Last year, the Climate Prediction Center's outlook called for a below-normal hurricane season in the Eastern Pacific basin with nine to fifteen named storms, with five to eight becoming hurricanes and one to three becoming major hurricanes. The actual season ended with eleven named storms of which ten became hurricanes and six became major hurricanes.
Meanwhile, in the Central Pacific basin, the Climate Prediction Center expects a below-normal season with two to four tropical cyclones. An average season in the Central Pacific, which begins on June 1, has four to five tropical cyclones, which include tropical depressions, tropical storms and hurricanes.
"Despite the forecast for a below-normal season, we encourage everyone to get prepared for the start of the season and stay on top of the forecasts as storms develop," said Ray Tanabe, the director of the Central Pacific Hurricane Center. "We've had two quiet seasons in a row here in the Central Pacific, but don't let your guard down. We should all be weather-ready this and every season."
Last year, the Climate Prediction Center's outlook called for a below-normal hurricane season in the Central Pacific basin with two to three tropical cyclones to affect the region. But no storms formed in the basin throughout 2011. Tropical Storm Fernanda formed in the Eastern Pacific before moving into the Central Pacific basin, but it weakened into a remnant low pressure system just hours later.
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