Much of the damages caused by Isaac is due to flooding—a peril not covered by a standard homeowners' insurance policy whether flooding is caused by rain or storm surge.

Up to 25 inches of rain fell in some spots in Louisiana, where Isaac made landfall twice as a Category 1 hurricane and the modelers agree Isaac's storm surge levels, which eclipsed some floodwalls, were high for a storm of Category 1 strength.

The AIR estimate assumes a 10 percent take-up rate for commercial flood policies.

Additionally, “Isaac's slow forward speed and refusal to dissipate will exacerbate wind damage,” says Tim Doggett, principal scientist at AIR.

Due to all the rain saturating the ground, trees can fall at lower wind speeds, he says. Roofs can become “fatigued and overloaded, causing additional damage,” as the wind persists, he adds.

Reported wind damage includes downed power lines and trees as well as some structures and items such as awnings, signage and trailers, AIR says.

More than half a million customers are still without power, according to reports from the local electric provider, Entergy.

Tornadoes spawned by the storm system remain a threat. Eqecat says nine tornadoes were reported in southern Mississippi and Alabama on August 29 and more were reported on Aug. 30.