By Harriet McLeod
CHARLESTON, South Carolina (Reuters) - Hurricane Irene's sheer size will create a huge impact, even if it falls short of being an epic Northeast coast storm for the history books, a geographer and hurricane historian said on Friday.
"It's probably not going to be one of those where it's the worst of the century," Cary Mock, an associate geography professor at the University of South Carolina, told Reuters.
However, said Mock, who has been studying hurricane history with grants from the National Science Foundation for more than 10 years, "it's about Hurricane Katrina-size, which is big. The storm surge is dependent not just on the winds but on the size."
Hurricanes are rare on the Northeast coast. Colder waters weaken them and hostile upper air currents usually tear them apart, said Mock, who is also a climatologist.
Hurricanes Bob in 1991, Gloria in 1985, and Donna in 1960 reached the Northeast. The 1938 storm called "The Long Island Express" or "The Great Hurricane of 1938" killed hundreds of people in New England.
"In New York and New England, just looking at the last 50 or 100 years is actually too small of a snapshot for a worst case scenario for hurricanes," Mock said.
He studies diaries, ships' logs and barometers from previous centuries for evidence of hurricanes that struck the Northeast coast long before hurricanes had names, or were even called hurricanes.
"They actually called them gales," he said, "or sometimes September gales because they noticed they happened in September."
In 1821, a major hurricane passed directly over New York City, "probably a strong category 4," Mock said. Historical records show it caused a 10-foot storm surge at low tide, Mock said. "At that time, not that many people were living in New York, so people didn't pay a lot of attention to it."
But William Redfield, the "father of hurricane science," observed the 1821 storm, Mock said.
Just as a debate goes on today over whether global warming causes more frequent or more intense hurricanes, the mid-19th century debate was over "the law of storms," Mock said.
Observers argued over what caused hurricanes and whether they were different from more familiar winter and spring nor'easters.
It took decades for them to learn that the two were formed by different meteorological processes, he said.
(Editing by Jerry Norton)