Hurricane Ivan cut a path of destruction across the Caribbean before becoming the third major hurricane to strike the United States in a month. Ivan and the other hurricanes that struck land recently are part of a trend of more and stronger hurricanes that will affect the people of the Caribbean and the United States for years to come.
First there was Charley, then Frances, and now Ivan; three major hurricanes in a month that have destroyed lives, homes and property across the Caribbean and the southeastern United States.
Hurricane forecasters say people who live in the region affected by hurricanes should not be surprised by the increased storm activity.
Scientists who study tropical weather patterns say beginning in 1995 air and water temperatures and circulation patterns in the Atlantic Ocean changed to become more favorable to the formation of more and much stronger storms. William Gray, an atmospheric scientist at Colorado State University says this phenomenon, known as a thermohaline circulation, lasts for decades and is what determines the cycle of hurricane activity.
"When this thermohaline circulation, Atlantic Ocean circulation feature goes fast we have more major storms forming in the Atlantic," he said. "When it slows we have fewer ones. Now it was going slow the first decades of the 20th century, then it was fast from about the middle 20th century to the late 60s. From the late 60s to the middle 90s it was going very slow, with many fewer major storms. Now, since '95 this is the 10th year that we feel the thermohaline has been growing stronger and eight of these last 10 years have been very busy."
Mr. Gray, one of the world's leading hurricane researchers, says people who live in the region affected by hurricanes have actually been very lucky during the past 10 years not to have been hit by more storms. He says weather patterns this year have changed somewhat to push more storms ashore.
"There are probably two basic reasons; one is that we have had a very active season so far, and the second is that the steering currents have been moving further west where they impact the United States and the Caribbean," he said.
William Gray also says the El Nino weather pattern that helps to move storms north into the mid Atlantic was absent this year, although he says a mild El Nino pattern has begun to emerge, which should make the end of the 2004 hurricane season less active than the first half. The Hurricane season ends on November 30.
Scientists say they do not know how long the current thermohaline circulation pattern will continue, but Professor Gray says if the future is like the past, the current pattern will continue for another 20 or 30 years. He says that means not only will there be more hurricanes, but there will be more of the stronger hurricanes that cause the most destruction.
With many more people living in coastal areas than there were during the last period of enhanced hurricane activity, Mr. Gray says the cost of hurricanes will be much higher.
"It is inevitable that we will see damage on a scale we have never previously seen, because if we are in this more active period it is not that we will have more storms than we had from the middle '20s to the middle '60s, but that there are so many more people and property in harms way, that it is inevitable that we see hurricane spawned damage on a level we have never previously seen," he said.
Professor Gray says one thing that is not causing increased hurricane activity is global warming, which some scientists have pointed to as a possible factor behind increased tropical storm activity.
Mr. Gray says hurricane activity follows a measurable pattern based on temperature changes and circulation patterns of air and water in the Atlantic Ocean. What is happening now, he says, is simply that pattern repeating itself, as it has done in the past, and will likely do in the future.