Shaping up to a hurricane-heavy year - Soundings Online

Shaping up to a hurricane-heavy year

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A second forecast is predicting an active hurricane season

A second forecast is predicting an active hurricane season

Boaters should brace for another active hurricane season. Citing warmer-than-average waters in the tropical Atlantic and other indicators, forecasters are calling for a higher than average number of tropical storms and hurricanes this summer and fall.

The National Oceanic and Atmospheric Administration in May released a seasonal outlook that forecasts 12 to 15 tropical storms this year, with six to eight systems becoming hurricanes and two of those major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Scale). The forecast is similar to one issued by Prof. William Gray, a noted hurricane researcher at the University of Colorado. In April his research team forecast an active year with 14 named storms, of which eight would be hurricanes and three intense hurricanes.

The busy season this year continues a trend that began in 1995, with the exception of the El Niño years of 1997 and 2002. (The weather phenomenon tends to stave off hurricane activity.) In previous years, there was an average of nine tropical storms, five hurricanes and one or two major hurricanes, according to NOAA.

Researchers have greatly honed their tracking skills, thanks in part to faster computers and better modeling, and now offer five-day forecasts instead of the traditional three-day. Last year hurricane watchers had a remarkably good record of predicting the correct paths of many of the storms. However, meteorologists haven’t fared well in predicting intensity; storms can suddenly pick up steam or weaken, and there is always a margin of error. Systems move quickly and can be unpredictable, so boaters who think they are clear of a hurricane’s path might not be.

“Normally there is an area of uncertainty,” says forecaster Lixion Avila of NOAA’s National Hurricane Center in Miami (www.nhc.noaa.gov). “The first thing to do is start reading advisories and keep informed.”

Federal officials recommend a “1-2-3” rule, which establishes a minimum recommended distance from a hurricane in the Atlantic. Allow at least a 100-mile error radius for a 24-hour forecast, 200-mile error radius for a 48-hour forecast, and 300-mile error radius for a 72-hour forecast. Larger buffer zones should be used in the case of forecast uncertainty, limited crew experience, and other factors.

Hurricane season is officially from June 1 to Nov. 30; however, the height of the season is August to October.

Hurricanes form in tropical regions where there is warm water (80 degrees F), moist air and converging equatorial winds. Most Atlantic hurricanes begin off the west coast of Africa, starting as thunderstorms that move out over the warm ocean. As warm, moist air rises from the ocean surface, water vapor condenses to form clouds. The condensation releases heat, which warms the cool air aloft and causes it to rise. The cycle continues as the rising air is replaced by more warm, humid air from the ocean. This exchange of heat from the surface creates a pattern of wind that circulates around a center.

High-pressure air in the upper atmosphere (above 30,000 feet) over the storm’s center cools the rising air, further driving the air cycle and hurricane’s growth. As high-pressure air is sucked into the low-pressure center of the storm, winds increase.

A tropical depression is an area of low pressure with swirling bands of rain and spiraling winds up to 39 miles per hour. It is considered a storm when winds exceed 39 mph and a hurricane when winds exceed 74 mph. Hurricanes are considered major if winds exceed 111 mph. In size, a hurricane can cover 50 to 1,000 miles, according to the Coast Guard.

Hurricane names are chosen by the World Meteorological Organization and are recycled every six years. Names of particularly destructive hurricanes often are retired. Storm names for this season are Alex, Bonnie, Charley, Danielle, Earl, Frances, Gaston, Hermine, Ivan, Jeanne, Karl, Lisa, Matthew, Nicole, Otto, Paula, Richard, Shary, Thomas, Virginie and Walter.

Last year’s hurricane season saw 14 named storms, including seven hurricanes and three major hurricanes. Perhaps the most memorable was Hurricane Isabel, which began as a slow-

moving tropical wave off Africa that rapidly intensified into a Category 4 storm as it approached the Mid-Atlantic states. It made landfall Sept. 18 in North Carolina. With 17 deaths directly attributed to the storm, high winds, historic high tides and $3 billion in damages, Isabel was the fiercest hurricane to hit the United States since Hurricane Mitch in 1998, and the worst hurricane in the Chesapeake Bay region since 1933.

The other major hurricanes were Fabian and Kate. Hurricane Fabian began as a tropical depression around Aug. 27, slamming Bermuda and then making its way to Nova Scotia. Kate developed around Sept. 25, criss-crossing the Atlantic and striking east of Newfoundland around Oct. 5.

One of the costliest hurricanes on record is Andrew, which blasted Florida Aug. 24, continued westward to the Gulf of Mexico where it turned north to Louisiana, and eventually merged with a frontal system over the mid-

Atlantic. Later reclassified from a Category 4 storm to a Category 5, Andrew caused 23 U.S. deaths (three in the Bahamas) and $26.5 billion in damage in the United States.