The first damage analysis of the slow-moving tropical system that deluged southern Louisiana last weekend is sobering. But for all the destruction it has caused, the low pressure system was not classified as a tropical storm or depression. Had it been a tropical cyclone, the storm would almost certainly rank among the 10 costliest hurricanes to strike the United States.

Louisiana newspaper The Advocate recently shared an analysis by the Baton Rouge Area Chamber. The analysis uses geographic information system data to study homes and businesses that had flooded in nine parishes in southeastern Louisiana. Some of the report's key findings include:

About 31% of homes (a total of 110,000 residences) within the nine parishes flooded.

The estimated value of homes located in flooded areas is $20.7 billion.

About 280,000 Baton Rouge metropolitan statistical area residents live in flooded areas.

As a region, a maximum of just 15% of all homes—not solely in the flood-impact areas—were insured against flooding.

Overall, 7,364 businesses employing 73,907 individuals are located in areas affected by floods. These represent 21% of businesses in the region.

Proportionally, businesses in Livingston experienced the most severe impact with 3,305 businesses that employ 27,653 employees in the areas of flood-impact, representing 91% of businesses and 94% of employees.

The $20.7 billion dollar figure for residential damages represents the estimated total value of residences in areas that flooded, not the actual damage. While that total will be significantly lower, this damage report does not include losses sustained to businesses, automobiles, or other personal items lost in the floodwaters. It will take some time before a total damage amount is released, which will include damage from insurers.

Katrina, which struck the northern Gulf coast in 2005, remains the costliest US tropical cyclone, with $125 billion (present-day dollars) in damages. It is followed by hurricanes Sandy and Ike, with Hurricane Frances rounding out the top 10 at $9.85 billion. The present Louisiana storm would almost certainly exceed Frances and slot somewhere in the top 10 if it were a genuine tropical cyclone.

Despite all of its tropical characteristics, the Louisiana storm never attained a closed circulation over water, and it never achieved storm-force winds. With access to ample warmth and moisture from the sizzling Gulf of Mexico, it essentially stalled out over Louisiana for from August 11-14, dropping in excess of 26 inches of rain over areas just east of Baton Rouge. In this part of Louisiana, the storm represented a 1,000-year flood event.

Because the vast majority of affected residences did not have flood insurance, tens of thousands of property owners in the Baton Rouge area will likely face a total loss. As the report concludes, "BRAC believes that this preliminary analysis begins to paint the compelling picture of the human toll inflicted by the flood, the magnitude of the impact it has already had on people where they live and work, and the potential challenges they face in the days, weeks, and months ahead." We agree.