"Isabel is a strong hurricane and is in a position that makes it a storm almost certain to make landfall along the East Coast of the U.S.," says Frederick J. Gadomski, Penn State meteorologist.
Usually, hurricanes have an even chance of moving off to the northeast, but with Isabel that is virtually impossible. According to Gadomski, an existing strong high pressure area in the Atlantic Ocean will prevent Isabel from going out to sea and ensure that she makes landfall along the mid Atlantic coast.
"The big worry is where the storm will make landfall and how intense it is when it does," says Gadomski.
Of concern in Pennsylvania is a 40-mile wide swath in eastern Pennsylvania covering the area between Harrisburg and Philadelphia and encompassing Scranton. A stationary storm yesterday (Sept 15) dropped more than six inches of rain in that area. If Isabel should produce heavy rains in eastern Pennsylvania in three or four days, a great potential for flooding exists, according to Gadomski.
"Historically, we have evidence that 100 miles either side of the hurricane center has the potential for 3 to 10 inches of rain in an 18-hour period," says Gadomski. "If Isabel comes in east of Cape Hatteras and into the Delmarva Peninsula and New Jersey coast moving northwest, it will move over the heart of Pennsylvania and all of the state will receive heavy rain.
"If Isabel makes landfall south of Cape Hatteras and into southern Virginia, the impact on Pennsylvania will be far less."
In the past, dying tropical storms have affected Pennsylvania, notably Hurricane Hazel in 1954 and tropical storm Agnes in 1972. While most people initially think of high winds and storm serges as the major dangers of hurricanes, these factors are only problems for those near the coast. The biggest problems related to hurricanes for the majority of people are water related.
"If Isabel comes into Pennsylvania, then eastern Pennsylvania, because of the recent storm, will have record floods," says Gadomski. Throughout the state, water tables are unusually high and streams that should be at low and dropping levels are high as well.
"The unusually wet summer primed the situation to be worse than it might have been after a normal summer," says Gadomski.