Unusual storm characteristics mean surprises could be in store for US insurers as claims from Hurricane Irene file in.

While the volume of claims is likely to be high in comparison to a typical hurricane, claim amounts likely will be low, according to a report from ratings agency Moody’s.

"Rather than direct severe damage from wind, we expect high levels of damage from such things as fallen trees, as well as minor structural damage," said vice president Paul Bauer.

"Although wind speeds and hurricane intensity were less than initially expected, a number of unique characteristics, such as the high levels of inland flooding, extensive power outages, and the very wide dispersion of the storm combine to create a high degree of uncertainty in terms of early loss estimates.”

"And because of these unusual factors, we suspect that as insurance claims are filed in the coming weeks, some surprises may be in store," Bauer continued.

Higher than usual automobile-related losses due to flooding, and high losses on both homeowners' and commercial insurance policies from power outages, are also expected.

Bauer said that widespread power outages caused numerous sump pump failures, in turn leading to water damage. A further complicating factor is that losses are likely to be unusually high in communities in mountainous areas that have been affected by heavy rains.

"Given Hurricane Irene's unusual characteristics, we believe modeled loss estimates will continue to vary widely, at least in the short term," Bauer said. "However, once companies begin to report their own internal estimates based on more accurate claims data, we expect that the hurricane will not prove to be a major capital or credit event for the P&C industry."

In addition, Moody's does not believe that losses will trigger reinsurance coverages, making this an insurance, rather than a reinsurance, event.