This comes from a CNN list -- it's in the sidebar on the right -- of the "Top 10 Deadliest" hurricanes. I read it while Katrina was strengthening in the Gulf of Mexico after crossing Florida. And now I just read it again:

9. New Orleans, Louisiana 1915
New Orleans, Louisiana
September 1915
Death toll: 275

This Category 4 storm caused Lake Pontchartrain to overflow its banks, killing 275 people. That scenario is one that hurricane experts don't like to ponder because if the city, surrounded on three sides by water, is hit by a major hurricane, the storm surge might inundate the city.

That phrase "don't like to ponder" resonates like a cracked bell today. This is one case where pessimism would have been preferable to hope.