Erika's arrival could remind US of hurricanes' costs

Craig Warga | NY Daily News Archive | Getty Images

A house burns as Hurricane Katrina ravaged New Orleans, 2005.

Now a tropical storm, Erika is forecast to sweep into South Florida early Monday as a hurricane. That's two days after the 10th anniversary of Hurricane Katrina's U.S. landfall, and the storm could serve as a stark reminder of the toll we pay for Mother Nature's wrath.

Until now, 2015 had been shaping up as another mild hurricane season in the U.S. But if the recent past is any guide, those storms will be more severe when they hit.

As Katrina's anniversary approached, the National Oceanic and Atmospheric Administration earlier this month updated its fall hurricane forecast with word that the odds of below-normal hurricane season are even better than it originally predicted in May.

NOAA researchers say there's a 90 percent chance that the number of named storms will be below-normal—up from a 70 percent chance forecast in May.

Read More Tropical Storm Erika strengthens, heads toward Florida

But that doesn't mean the storms won't be nasty when they strike.

"Tropical storms and hurricanes can and do strike the United States, even in below-normal seasons and during El Nino events," Gerry Bell, lead seasonal hurricane forecaster with NOAA's Climate Prediction Center, told Reuters, warning that those living along the Atlantic and Gulf coasts need to stay prepared for tropical storms

A forecast for fewer storms doesn't mean milder storms. A review of government data over the past four decades shows that more than half of the $43 billion in flood damage since 1978 was caused by just two: Hurricane Katrina in 2007 and Superstorm Sandy in 2012. (Technically, the last major hurricane to hit U.S. shores—ranking at least a Category 3 on the Saffir-Simpson Hurricane Wind Scale—was Wilma in October 2005. Sandy was a hurricane but its wind speed dipped below hurricane strength, and it was considered a post-tropical cyclone when it made U.S. landfall. Other more recent hurricanes, including the especially destructive Ike and Gustav in 2008, were below Category 3 when they hit the U.S.)

Between 1978 and 2000, the average cost of damage covered by federal flood insurance amounted to less than $500 million, and just one year—1995 exceeded $1 billion. Since 2001, that payout has jumped to an average of nearly $3 billion a year.

Scientists have warned that the cost of major storms is rising along with sea levels, creating a greater flooding hazard for coastal communities. The frequency of these storm surges has increased significantly over the past century, according to a paper published last month in a peer-reviewed journal, Nature Climate Change.

The researchers found that in New York City, for example, storm conditions that create a higher risk of flooding are twice as likely today than in the mid-20th century.

This year's NOAA forecast calls for six to 11 tropical storms, with three to six reaching hurricane-force winds of 74 mph. Two of the major hurricanes could bring winds of at least 111 miles per hour.

Last year, there were eight named storms, including six hurricanes.

Correction: An earlier version incorrectly stated when the last hurricane hit the U.S.