The record-setting 2004 Atlantic hurricane season has almost two more months to churn up trouble, but it already reminds veteran tropical storm predictor James O'Brien of the Wild West.
"It was like ducking bullets from all directions," said Mr. O'Brien, who is director of the Center for Ocean-Atmosphere Prediction Studies at Florida State University in Tallahassee. "The thing that impresses me is that four hurricanes missed me." Tallahassee, located in the state's panhandle, so far has escaped largely unscathed.
If Mr. O'Brien and other hurricane forecasters are right, there will be an unusual number of meteorological bullets like Charley, Ivan, Jeanne, and Frances to duck in the future. Those 2004 storms made Florida the first state hit by four hurricanes in one season since Texas in 1886.
They believe that the world has shifted gears into a cycle of increased hurricane activity that may last 20 years.
By all accounts, Ohio and other northern states also face decades of greater travail from hurricanes and their remnants. After landfall in Florida or other coastal states, hurricanes usually weaken into tropical storms or depressions. Although the winds are less damaging, the remnants of hurricanes have long arms and pack torrential rains that can reach far north of the hurricanes' landfalls.
Ivan's remains, for instance, caused widespread flooding in Pennsylvania, West Virginia, and southern Ohio.
Rain from the remnants of Hurricane Ivan caused the Ohio River to rise at a rate of 22 feet in 24 hours, the fastest rate in the river's recorded history. When the river crested on Sept. 19, the Marietta Times reported, the river stood at 44.97 feet, 10 feet above flood stage in the waterlogged Ohio River town.
The storm dumped up to 9 inches of rain on Western Pennsylvania, triggering floods and mudslides that damaged or destroyed thousands of homes, businesses, bridges, and roads in Allegheny County and surrounding areas.
The idea of hurricanes causing damage in the Great Lakes region brings a typical response, according to William Deedler, historian at the National Weather Service in Detroit. "What? Hurricanes here in the Great Lakes? No way!"
In reality, however, remnants of hurricanes or tropical storms chug through the region on an average of twice a decade, according to Mr. Deedler. Opal arrived in 1995, Fran in 1996, and Isabel in 2003 churned up waves all across Lake Erie and into Canada.
Authorities are still adding up the nationwide damage, but 2004 already may be the costliest hurricane season in United States history. There have been more than 130 deaths in the continental United States. Jeanne alone killed at least 1,500 people in Haiti, with more than 1,000 others missing.
"We are a decade into the active phase of a natural 60-year, or so, cycle of hurricane activity," said Dr. Hugh Willoughby of the International Hurricane Research Center in Miami. "This season is active, but not dramatically more so than others since 1995."
The last cycle of intense hurricane activity ran from 1910-1960, peaking from the 1930s through the 1950s. Then it shifted into an inactive phase that ended in 1995.
"Since 1995, the level of hurricane activity has again been on the rise," said COAPS meteorologist David Zierden. "Experts believe this new level of increased hurricane activity will last another 20 or more years."
In the nine-year period from 1995 to 2003, there were a record 122 tropical storms big enough to get an official name, 69 hurricanes, and a near-record 32 major hurricanes. Those are Category 3 storms on the Saffir-Simpson Hurricane Scale, with sustained winds of 111-130 miles per hour. Although major hurricanes account for barely 25 per cent of all named storms, they cause 85 percent of the total damage.
That nine-year period also stands as a record based on the National Oceanic and Atmospheric Administration hurricane season index. Called the accumulated Cyclone Energy Index, it takes into account the number of storms that develop, their wind strength, and how long they last.
Since 1995, the index has averaged 139.6. That is 50 per cent above the 54-year average of 93.2 from 1950 through 2003. The increase occurred despite low indexes in 1997 and 2002. In those years, El Nino events occurred, an unusual warming of the ocean surface off the western coast of South America that suppress hurricane activity.
The increased activity since 1995 is due to an immense flow of Atlantic Ocean water, equal to 100 Amazon Rivers, which controls the hurricane cycle. The flow exists because of differences in the density of seawater, which depends on temperature (thermal) and saltiness or salinity (haline).
Called the Atlantic "thermohaline" circulation, it transports warm, salty water to the north, where the water cools and sinks into the deep ocean. That water flows southward. When seawater in the North Atlantic is warm and salty, it sinks quickly into the deep ocean, and the circulation system runs fast. When seawater is cooler and fresher, the circulation slows down.
Most Atlantic hurricanes begin as thunderstorms that march off the west coast of Africa. The storms move west, and intensify as they pick up energy from warm, tropical ocean waters. For the storms to change into hurricanes, certain wind conditions must exist in the tropical Atlantic.
In a complicated chain of cause-and-effect, a slower thermohaline circulation changes tropical Atlantic wind patterns in ways that suppress hurricanes. Faster circulation causes winds that favor formation of more hurricanes.
"That's the pattern we're in now," said Mr. Willoughby.
Like other hurricane forecasters, he questions whether global warming is playing a major role in the increased hurricane activity. Although global climate change often is the scapegoat for extreme weather of all kinds, the actual scientific evidence on its effects is limited.
"Various groups and individuals have suggested that the recent large upswing in Atlantic hurricane activity may be in some way related to the effects of increased manmade greenhouse gases such as carbon dioxide," said William Gray, the Colorado State University scientist who pioneered hurricane forecasting. "There is no reasonable scientific way that such an interpretation of this recent upward shift in Atlantic hurricane activity can be made."
Studies do hint that global warming can supply the heat and energy to make strong hurricanes even stronger, creating monster storms such as Ivan in September and Isabel in 2003. With sustained winds above 155 mph, both were Category 5 storms, the most powerful of all hurricanes, which weakened before making landfall.
A warmer globe, however, has a more limited effect on the total number of hurricanes and where they make landfall, Mr. Willoughby noted.
Although the 2004 hurricane season may seem unusually severe, meteorologists see it as simply a continuation of the ratcheted-up cycle since 1995.
Hurricane season, the time when most hurricanes occur, runs from June 1-Nov. 30. The 2004 version got off to a slow start. It took until Aug. 1 for the first named tropical storm, Alex, to appear. That has happened only three times in the last 15 years. But it made up for lost time, with a lot of activity compressed into two months.
An average season brings 10 tropical storms strong enough to get names. About six reach hurricane strength and two reach the Category 3 level and become major hurricanes.
Mr. Gray predicted 14 named storms, eight hurricanes, and three major hurricanes. NOAA predicted a 50 percent chance of an above-normal season, with 12 to 15 tropical storms, six to eight hurricanes, and two to four major hurricanes.
So far there have been 12 named storms, with seven hurricanes: Alex, Charley, Danielle, Frances, Ivan, Jeanne, and Karl. Four were major storms. The eight tropical storms that formed in August broke the previous record of seven set in 1933 and 1995.
Mr. Willoughby cited one quirk in the 2004 hurricane season that puzzles and concerns forecasters. "What's different now is that a greater proportion of the hurricanes are striking the U. S. coastline. Is this season the start of a regime in which a greater proportion of Atlantic hurricanes strike Florida?"
Meteorologists don't know. Hurricane landfalls did increase during parts of the last active hurricane cycle. For the cycle that started in 1995, however, this is the first year in which landfalls also have increased. In an average year one or two hurricanes hit land on the Atlantic or Gulf coasts. Four have done it so far in 2004.
Storm-weary people may have gotten good news in September when NOAA reported that an El Nino event was developing in the Pacific Ocean. If the warming of ocean water intensifies, El Nino could bring weather conditions unfavorable for hurricane formation in 2006. Hurricane seasons in El Nino years tend to be mild.
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