While coastal residents from Maryland to the Carolinas pick up the wreckage from Isabel, meteorologists are warning East Coast communities to prepare for busier hurricane seasons for the next 10 to 40 years.
Higher sea surface temperatures and favorable wind conditions in the Atlantic since 1995 have more than doubled the number of major storms roaring out of the tropics each year. Those affecting the Caribbean have quintupled, and the rare ones that strike in October or later have jumped tenfold.
Hazel brought storm tides 2 to 6 feet above normal to the Chesapeake, with 73-mph winds. It killed six Marylanders, flooded streets around Baltimore Harbor, blew roofs away and floated homes off their foundations.
"If you look back at the 1950s ... it was year after year of these major hurricanes ramming into the East Coast. And we would not be shocked to see that take place again," said Stanley B. Goldenberg, a meteorologist with the National Oceanic and Atmospheric Administration's hurricane research division.
Population increases and intense coastal development since the 1960s are likely to produce a correspondingly higher toll in lives and dollars, he said.
Goldenberg was the lead author of a 2001 paper in the journal Science that first noted the return of higher hurricane activity in the Atlantic. The pattern, which began in 1995, is striking - and it has persisted.
"You have to be deliberately blind not to see that something is going on here," he said.
This is not the result of global warming. There is evidence that these long-term hurricane cycles - which can last up to 40 years from peak to peak - stretch at least to the 1600s, Goldenberg said.
They're even clearer in the more abundant data gathered since 1900, which show a period of low activity through the mid-1920s followed by higher activity through the 1960s.
But reliable data on Atlantic hurricanes did not became available until 1944, when aircraft - and later satellites - began tracking storms at sea that had previously gone unnoticed.
Goldenberg and his colleagues found an average of 2.7 "major" hurricanes a year in the active period from 1944 to 1970.
These intense storms have sustained winds above 110 mph - Category 3, 4 or 5 on the Saffir-Simpson scale. Although they constitute 20 percent of all tropical storms, they cause 80 percent of the damage.
In 1970, something changed. The hurricane seasons became much quieter, and the average number of major storms fell to 1.5 per year. There were no Category 4 or 5 storms for 15 years.
But in 1995 the pendulum swung back. That year saw one of the most active Atlantic storm seasons on record, with 19 named storms, five of them major. And a pattern was set. The six years from 1995 to 2000 averaged 3.8 major storms per year - even busier than the 1950s and 1960s.
"We don't expect the system to switch back anytime soon," Goldenberg said.
None of this activity is perfectly consistent. Even a busy hurricane era will produce slow years, Goldenberg said, just as the "low-activity" era that ended in 1994 produced some ferocious storms. Those included Andrew, which devastated south Florida in 1992, and Hugo, which battered Charleston, S.C., in 1989.
Nor will every hurricane season during an active era produce East Coast landfalls. Goldenberg said Eastern states have been shielded by a persistent atmospheric pattern that has steered many storms out to sea.
But "we expect things to shift," he said. Florida was a frequent target in the 1940s, before the bull's-eye shifted to the East Coast during the 1950s and to the Gulf Coast in the 1960s.
Isabel may be gone, but need for caution lingers, scientists say
Hurricane cycle means busier storm seasons for East Coast in near future; Same conditions spawned Hazel
We've upgraded our reader commenting system. Learn more about the new features.
The Baltimore Sun encourages civil dialogue related to our stories; you must register and log-in to our site in order to participate. We reserve the right to remove any user and to delete comments that violate our Terms of Service. By commenting, you agree to these terms. Please flag inappropriate comments.