PENNSYLVANIA, USA — As we remember the devastation caused by Agnes 50 years ago, we only have to look back ten years or even one, for major damage caused by tropical activity in our area.
From Lee in 2011 to Fred, Ida and Isaias of the last two years, Pennsylvania continues to see increased tropical activity.
"Storms that used to be called 100-year return period storms, we're now seeing those with a ten-year return period," Dr. James Kinter, III said. Dr. Kinter is a climatologist and the head of the Center for Ocean-Land-Atmosphere Studies at George Mason University.
"So they've gotten ten times more frequent. That means we see flash flood events much more frequently," Kinter said.
The main source for energy in tropical cyclones lies in the temperature of the ocean. Think of a tropical storm as a heat pump, moving heat from one reservoir to another. The bigger the difference, the stronger the energy for the pump.
The bigger the difference between the ocean temperature and the cooler air in the troposphere, the stronger the storm.
And it's a phenomena we're already seeing.
"We're seeing a shift.. of tropical cyclone intensity to the higher intensity storms," Dr. Kinter said.
Scientists say they're also seeing a shift in the path of tropical storms. Think about the path of Ida, Isaias and Fred. Those systems were able to survive a bit longer inland and keep intensity.
"What we are seeing is evidence of a changing climate," Kelton Halbert said. Halbert is a doctoral student at the University of Wisconsin. His specialty includes severe thunderstorms, supercells and tornadoes. New data in his fields blends over into tropical activity.
A reanalysis of data from the National Centers for Environmental Prediction (NCEP) found that since 1979, the number of days with enough energy in the atmosphere for thunderstorm development has increased by forty days in our region. That simply means we are warmer with more moisture more often. However, that means we regularly have more energy in the atmosphere.
"You're going to see more sustained development as tropical storms make landfall," Halbert said. "You'll see impacts further inland because it takes longer for it to weaken."
And, with more energy in the atmosphere, what would that mean for the next storm like Agnes?
"The possibility that a storm would follow a similar path over the Chesapeake Bay is very alarming," Dr. Kinter said. "If a storm did that, it would be Agnes on steroids."