This year's hurricane season — which officially came to a close Friday — proved to be one of the most active on record, with Hurricanes Isaac and Sandy wreaking havoc on two coastlines, although both storms, technically, did not meet the definition of "major" hurricanes.
"This year proved that it's wrong to think that only major hurricanes can ruin lives and impact local economies," said Laura Furgione, acting director of the National Weather Service.
This season ranks third among the most active since record-keeping began in 1851 with 19 named storms, 10 of them hurricanes — although only one, Michael, was strong enough to be considered a "major" hurricane — and it never made landfall. Sandy was a Category 2, Isaac a Category 1.
On Thursday, forecasters at the Tropical Meteorology Project at Colorado State University issued a report noting they had "significantly under-predicted named storms and named storm days, while we over-predicted more intense hurricane activity for the entire Atlantic basin."
Usually, the Atlantic sees a dozen named storms a season, half of them hurricanes, half of those major storms, according to John Cangialosi, a hurricane specialist at the National Hurricane Center in Miami.
The season also began earlier than usual, with tropical storms Alberto and Beryl arriving before June 1, and tied with the last two years, as well as 1995 and 1887, for the third-most tropical storms on record. There were more storms only in 2005 (28), and in 1933 (21), according to the National Hurricane Center.
This was first season with only one major hurricane in five years, less than what the National Oceanic and Atmospheric Administration had predicted in August: five to eight hurricanes, two to three of them "major," meaning they rated categories 3 to 5 on the Saffir-Simpson hurricane scale. Michael was a Category 3.
The scale was developed in 1971 by civil engineer Herbert Saffir and meteorologist Robert Simpson, then director of the National Hurricane Center, to classify storms based on wind measurements.
According to the National Hurricane Center, a Category 1 hurricane generates "very dangerous winds" of 75 to 95 mph, strong enough to damage roofs, topple trees and power lines.
By contrast, a Category 3 hurricane packs winds of 111 mph or more and can cause "devastating damage" to homes, snapping many trees, blocking roads and leaving areas without water or power for weeks.
Hurricane Isaac was a Category 1 when it made landfall in Louisiana on Aug. 28, eventually killing nine people and causing up to $1.5 billion in damages, primarily from flooding associated with heavy rain and storm surge.
Sandy, the most powerful storm this season, peaked as a Category 2, weakened and was no longer even a hurricane according to Saffir-Simpson when it made landfall in New Jersey on Oct. 29, killing 125 people across the region and causing $62 billion in damages, making it the second-costliest storm in U.S. history after Hurricane Katrina in 2005, which caused about $128 billion in damages, adjusting for inflation.
Both storms illustrate the danger of judging hurricanes according to their category on the familiar scale, weather experts said.